mdbx.h++

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#pragma once
 
//
// Tested with, since 2026:
//  - Elbrus LCC >= 1.28 (http://www.mcst.ru/lcc);
//  - GNU C++ >= 11.3;
//  - CLANG >= 14.0;
//  - MSVC >= 19.44 (Visual Studio 2022 toolchain v143),
// before 2026:
//  - Elbrus LCC >= 1.23 (http://www.mcst.ru/lcc);
//  - GNU C++ >= 4.8;
//  - CLANG >= 3.9;
//  - MSVC >= 14.0 (Visual Studio 2015),
//    but 19.2x could hang due optimizer bug;
//  - AppleClang, but without C++20 concepts.
//
 
/* Workaround for modern libstdc++ with CLANG < 4.x */
#if defined(__SIZEOF_INT128__) && !defined(__GLIBCXX_TYPE_INT_N_0) && defined(__clang__) && __clang_major__ < 4
#define __GLIBCXX_BITSIZE_INT_N_0 128
#define __GLIBCXX_TYPE_INT_N_0 __int128
#endif /* Workaround for modern libstdc++ with CLANG < 4.x */
 
#if !defined(__cplusplus) || __cplusplus < 201103L
#if !defined(_MSC_VER) || _MSC_VER < 1900
#error "C++11 compiler or better is required"
#elif _MSC_VER >= 1910
#error "Please add `/Zc:__cplusplus` to MSVC compiler options to enforce it conform ISO C++"
#endif /* MSVC is mad and don't define __cplusplus properly */
#endif /* __cplusplus < 201103L */
 
#if (defined(_WIN32) || defined(_WIN64)) && MDBX_WITHOUT_MSVC_CRT
#error "CRT is required for C++ API, the MDBX_WITHOUT_MSVC_CRT option must be disabled"
#endif /* Windows */
 
#ifndef __has_include
#define __has_include(header) (0)
#endif /* __has_include */
 
#if __has_include(<version>)
#include <version>
#endif /* <version> */
 
/* Disable min/max macros from C' headers */
#ifndef NOMINMAX
#define NOMINMAX
#endif
 
#include <algorithm>   // for std::min/max
#include <cassert>     // for assert()
#include <climits>     // for CHAR_BIT
#include <cstring>     // for std::strlen, str:memcmp
#include <exception>   // for std::exception_ptr
#include <ostream>     // for std::ostream
#include <sstream>     // for std::ostringstream
#include <stdexcept>   // for std::invalid_argument
#include <string>      // for std::string
#include <type_traits> // for std::is_pod<>, etc.
#include <utility>     // for std::make_pair
#include <vector>      // for std::vector<> as template args
 
#if defined(__cpp_lib_memory_resource) && __cpp_lib_memory_resource >= 201603L
#include <memory_resource>
#endif
 
#if defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L
#include <string_view>
#endif
 
#ifndef MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM
#ifdef INCLUDE_STD_FILESYSTEM_EXPERIMENTAL
#define MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM 1
#elif defined(__cpp_lib_filesystem) && __cpp_lib_filesystem >= 201703L && __cplusplus >= 201703L
#define MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM 0
#elif (!defined(_MSC_VER) || __cplusplus >= 201403L ||                                                                 \
       (defined(_MSC_VER) && defined(_SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING) && __cplusplus >= 201403L))
#if defined(__cpp_lib_experimental_filesystem) && __cpp_lib_experimental_filesystem >= 201406L
#define MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM 1
#elif defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L && __has_include(<experimental/filesystem>)
#define MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM 1
#else
#define MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM 0
#endif
#else
#define MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM 0
#endif
#endif /* MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM */
 
#if MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM
#include <experimental/filesystem>
#elif defined(__cpp_lib_filesystem) && __cpp_lib_filesystem >= 201703L
#include <filesystem>
#endif
 
#if defined(__cpp_lib_span) && __cpp_lib_span >= 202002L
#include <span>
#endif
 
#if !defined(_MSC_VER) || defined(__clang__)
#define MDBX_EXTERN_API_TEMPLATE(API_ATTRIBUTES, ...) extern template class API_ATTRIBUTES __VA_ARGS__
#define MDBX_INSTALL_API_TEMPLATE(API_ATTRIBUTES, ...) template class __VA_ARGS__
#else
#define MDBX_EXTERN_API_TEMPLATE(API_ATTRIBUTES, ...) extern template class __VA_ARGS__
#define MDBX_INSTALL_API_TEMPLATE(API_ATTRIBUTES, ...) template class API_ATTRIBUTES __VA_ARGS__
#endif
 
#if defined(_MSC_VER) && _MSC_VER >= 1900
#define MDBX_MSVC_DECLSPEC_EMPTY_BASES __declspec(empty_bases)
#else
#define MDBX_MSVC_DECLSPEC_EMPTY_BASES /* nope */
#endif                                 /* _MSC_VER >= 1900 */
 
#if __cplusplus >= 201103L
#include <chrono>
#include <ratio>
#endif
 
#include "mdbx.h"
 
#if (defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L) ||                                                  \
    (defined(__cpp_lib_endian) && __cpp_lib_endian >= 201907L) ||                                                      \
    (defined(__cpp_lib_bitops) && __cpp_lib_bitops >= 201907L) ||                                                      \
    (defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L)
#include <bit>
#elif !(defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && defined(__ORDER_BIG_ENDIAN__))
#if defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && defined(__BIG_ENDIAN)
#define __ORDER_LITTLE_ENDIAN__ __LITTLE_ENDIAN
#define __ORDER_BIG_ENDIAN__ __BIG_ENDIAN
#define __BYTE_ORDER__ __BYTE_ORDER
#elif defined(_BYTE_ORDER) && defined(_LITTLE_ENDIAN) && defined(_BIG_ENDIAN)
#define __ORDER_LITTLE_ENDIAN__ _LITTLE_ENDIAN
#define __ORDER_BIG_ENDIAN__ _BIG_ENDIAN
#define __BYTE_ORDER__ _BYTE_ORDER
#else
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_BIG_ENDIAN__ 4321
#if defined(__LITTLE_ENDIAN__) || (defined(_LITTLE_ENDIAN) && !defined(_BIG_ENDIAN)) || defined(__ARMEL__) ||          \
    defined(__THUMBEL__) || defined(__AARCH64EL__) || defined(__MIPSEL__) || defined(_MIPSEL) || defined(__MIPSEL) ||  \
    defined(_M_ARM) || defined(_M_ARM64) || defined(__e2k__) || defined(__elbrus_4c__) || defined(__elbrus_8c__) ||    \
    defined(__bfin__) || defined(__BFIN__) || defined(__ia64__) || defined(_IA64) || defined(__IA64__) ||              \
    defined(__ia64) || defined(_M_IA64) || defined(__itanium__) || defined(__ia32__) || defined(__CYGWIN__) ||         \
    defined(_WIN64) || defined(_WIN32) || defined(__TOS_WIN__) || defined(__WINDOWS__)
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#elif defined(__BIG_ENDIAN__) || (defined(_BIG_ENDIAN) && !defined(_LITTLE_ENDIAN)) || defined(__ARMEB__) ||           \
    defined(__THUMBEB__) || defined(__AARCH64EB__) || defined(__MIPSEB__) || defined(_MIPSEB) || defined(__MIPSEB) ||  \
    defined(__m68k__) || defined(M68000) || defined(__hppa__) || defined(__hppa) || defined(__HPPA__) ||               \
    defined(__sparc__) || defined(__sparc) || defined(__370__) || defined(__THW_370__) || defined(__s390__) ||         \
    defined(__s390x__) || defined(__SYSC_ZARCH__)
#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
#endif
#endif
#endif /* Byte Order */

#if defined(DOXYGEN)
#define MDBX_CXX17_CONSTEXPR constexpr
#elif defined(__cpp_constexpr) && __cpp_constexpr >= 201603L &&                                                        \
    ((defined(_MSC_VER) && _MSC_VER >= 1915) || (defined(__clang__) && __clang_major__ > 5) ||                         \
     (defined(__GNUC__) && __GNUC__ > 7) || (!defined(__GNUC__) && !defined(__clang__) && !defined(_MSC_VER)))
#define MDBX_CXX17_CONSTEXPR constexpr
#else
#define MDBX_CXX17_CONSTEXPR inline
#endif /* MDBX_CXX17_CONSTEXPR */

#if defined(DOXYGEN)
#define MDBX_CXX20_CONSTEXPR constexpr
#elif defined(__cpp_lib_is_constant_evaluated) && __cpp_lib_is_constant_evaluated >= 201811L &&                        \
    defined(__cpp_lib_constexpr_string) && __cpp_lib_constexpr_string >= 201907L
#define MDBX_CXX20_CONSTEXPR constexpr
#else
#define MDBX_CXX20_CONSTEXPR inline
#endif /* MDBX_CXX20_CONSTEXPR */
 
#if CONSTEXPR_ENUM_FLAGS_OPERATIONS || defined(DOXYGEN)
#define MDBX_CXX01_CONSTEXPR_ENUM MDBX_CXX01_CONSTEXPR
#define MDBX_CXX11_CONSTEXPR_ENUM MDBX_CXX11_CONSTEXPR
#define MDBX_CXX14_CONSTEXPR_ENUM MDBX_CXX14_CONSTEXPR
#define MDBX_CXX17_CONSTEXPR_ENUM MDBX_CXX17_CONSTEXPR
#define MDBX_CXX20_CONSTEXPR_ENUM MDBX_CXX20_CONSTEXPR
#else
#define MDBX_CXX01_CONSTEXPR_ENUM inline
#define MDBX_CXX11_CONSTEXPR_ENUM inline
#define MDBX_CXX14_CONSTEXPR_ENUM inline
#define MDBX_CXX17_CONSTEXPR_ENUM inline
#define MDBX_CXX20_CONSTEXPR_ENUM inline
#endif /* CONSTEXPR_ENUM_FLAGS_OPERATIONS */

#if defined(CONSTEXPR_ASSERT)
#define MDBX_CONSTEXPR_ASSERT(expr) CONSTEXPR_ASSERT(expr)
#elif defined NDEBUG
#define MDBX_CONSTEXPR_ASSERT(expr) void(0)
#else
#define MDBX_CONSTEXPR_ASSERT(expr) ((expr) ? void(0) : [] { assert(!#expr); }())
#endif /* MDBX_CONSTEXPR_ASSERT */
 
#ifndef MDBX_LIKELY
#if defined(DOXYGEN) || (defined(__GNUC__) || __has_builtin(__builtin_expect)) && !defined(__COVERITY__)
#define MDBX_LIKELY(cond) __builtin_expect(!!(cond), 1)
#else
#define MDBX_LIKELY(x) (x)
#endif
#endif /* MDBX_LIKELY */
 
#ifndef MDBX_UNLIKELY
#if defined(DOXYGEN) || (defined(__GNUC__) || __has_builtin(__builtin_expect)) && !defined(__COVERITY__)
#define MDBX_UNLIKELY(cond) __builtin_expect(!!(cond), 0)
#else
#define MDBX_UNLIKELY(x) (x)
#endif
#endif /* MDBX_UNLIKELY */

#if defined(DOXYGEN)
#define MDBX_IF_CONSTEXPR constexpr
#elif defined(__cpp_if_constexpr) && __cpp_if_constexpr >= 201606L
#define MDBX_IF_CONSTEXPR constexpr
#else
#define MDBX_IF_CONSTEXPR
#endif /* MDBX_IF_CONSTEXPR */
 
#if defined(DOXYGEN) || (__has_cpp_attribute(fallthrough) && (!defined(__clang__) || __clang__ > 4)) ||                \
    __cplusplus >= 201703L
#define MDBX_CXX17_FALLTHROUGH [[fallthrough]]
#else
#define MDBX_CXX17_FALLTHROUGH
#endif /* MDBX_CXX17_FALLTHROUGH */
 
#if defined(DOXYGEN) || (__has_cpp_attribute(likely) >= 201803L && (!defined(__GNUC__) || __GNUC__ > 9))
#define MDBX_CXX20_LIKELY [[likely]]
#else
#define MDBX_CXX20_LIKELY
#endif /* MDBX_CXX20_LIKELY */
 
#ifndef MDBX_CXX20_UNLIKELY
#if defined(DOXYGEN) || (__has_cpp_attribute(unlikely) >= 201803L && (!defined(__GNUC__) || __GNUC__ > 9))
#define MDBX_CXX20_UNLIKELY [[unlikely]]
#else
#define MDBX_CXX20_UNLIKELY
#endif
#endif /* MDBX_CXX20_UNLIKELY */
 
#ifndef MDBX_HAVE_CXX20_CONCEPTS
#if defined(__cpp_concepts) && __cpp_concepts >= 202002L && defined(__cpp_lib_concepts) && __cpp_lib_concepts >= 202002L
#include <concepts>
#define MDBX_HAVE_CXX20_CONCEPTS 1
#elif defined(DOXYGEN)
#define MDBX_HAVE_CXX20_CONCEPTS 1
#else
#define MDBX_HAVE_CXX20_CONCEPTS 0
#endif /* <concepts> */
#endif /* MDBX_HAVE_CXX20_CONCEPTS */
 
#ifndef MDBX_CXX20_CONCEPT
#if MDBX_HAVE_CXX20_CONCEPTS || defined(DOXYGEN)
#define MDBX_CXX20_CONCEPT(CONCEPT, NAME) CONCEPT NAME
#else
#define MDBX_CXX20_CONCEPT(CONCEPT, NAME) typename NAME
#endif
#endif /* MDBX_CXX20_CONCEPT */
 
#ifndef MDBX_ASSERT_CXX20_CONCEPT_SATISFIED
#if MDBX_HAVE_CXX20_CONCEPTS || defined(DOXYGEN)
#define MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(CONCEPT, TYPE) static_assert(CONCEPT<TYPE>)
#else
#define MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(CONCEPT, NAME)                                                             \
  static_assert(true, MDBX_STRINGIFY(CONCEPT) "<" MDBX_STRINGIFY(TYPE) ">")
#endif
#endif /* MDBX_ASSERT_CXX20_CONCEPT_SATISFIED */
 
#ifdef _MSC_VER
#pragma warning(push, 4)
#pragma warning(disable : 4127) /* conditional expression is constant */
#pragma warning(disable : 4251) /* 'std::FOO' needs to have dll-interface to                                           \
                                   be used by clients of 'mdbx::BAR' */
#pragma warning(disable : 4275) /* non dll-interface 'std::FOO' used as                                                \
                                   base for dll-interface 'mdbx::BAR' */
/* MSVC is mad and can generate this warning for its own intermediate
 * automatically generated code, which becomes unreachable after some kinds of
 * optimization (copy elision, etc). */
#pragma warning(disable : 4702) /* unreachable code */
#endif                          /* _MSC_VER (warnings) */
 
#if defined(__LCC__) && __LCC__ >= 126
#pragma diagnostic push
#if __LCC__ < 127
#pragma diag_suppress 3058 /* workaround: call to is_constant_evaluated()                                              \
                              appearing in a constant expression `true` */
#pragma diag_suppress 3060 /* workaround: call to is_constant_evaluated()                                              \
                              appearing in a constant expression `false` */
#endif
#endif /* E2K LCC (warnings) */
 
//------------------------------------------------------------------------------
namespace mdbx {


#if defined(DOXYGEN) || (defined(__cpp_char8_t) && __cpp_char8_t >= 201811)
using byte = char8_t;
#else
// Avoid `std::byte` since it doesn't add features but inconvenient restrictions.
using byte = unsigned char;
#endif /* __cpp_char8_t >= 201811*/
 
#if defined(__cpp_lib_endian) && __cpp_lib_endian >= 201907L
using endian = ::std::endian;
#elif defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && defined(__ORDER_BIG_ENDIAN__)
enum class endian { little = __ORDER_LITTLE_ENDIAN__, big = __ORDER_BIG_ENDIAN__, native = __BYTE_ORDER__ };
#else
#error "Please use a C++ compiler provides byte order information or C++20 support"
#endif /* Byte Order enum */

using version_info = ::MDBX_version_info;
MDBX_CXX11_CONSTEXPR const version_info &get_version() noexcept;
using build_info = ::MDBX_build_info;
MDBX_CXX11_CONSTEXPR const build_info &get_build() noexcept;

static MDBX_CXX17_CONSTEXPR size_t strlen(const char *c_str) noexcept;

static MDBX_CXX20_CONSTEXPR void *memcpy(void *dest, const void *src, size_t bytes) noexcept;
static MDBX_CXX20_CONSTEXPR int memcmp(const void *a, const void *b, size_t bytes) noexcept;

using legacy_allocator = ::std::string::allocator_type;

#if defined(DOXYGEN)
#define MDBX_CXX_HAS_POLYMORPHIC_ALLOCATOR 1
#elif !defined(MDBX_CXX_HAS_POLYMORPHIC_ALLOCATOR)
#if defined(__cpp_lib_memory_resource) && __cpp_lib_memory_resource >= 201603L &&                                      \
    (!defined(_GLIBCXX_USE_CXX11_ABI) || _GLIBCXX_USE_CXX11_ABI)
#define MDBX_CXX_HAS_POLYMORPHIC_ALLOCATOR 1
#else
#define MDBX_CXX_HAS_POLYMORPHIC_ALLOCATOR 0
#endif
#endif /* MDBX_CXX_HAS_POLYMORPHIC_ALLOCATOR */
 
#if defined(DOXYGEN) || MDBX_CXX_HAS_POLYMORPHIC_ALLOCATOR
using polymorphic_allocator = ::std::pmr::string::allocator_type;
using default_allocator = polymorphic_allocator;
#else
using default_allocator = legacy_allocator;
#endif /* MDBX_CXX_HAS_POLYMORPHIC_ALLOCATOR */
 
struct slice;
struct default_capacity_policy;
template <class ALLOCATOR = default_allocator, class CAPACITY_POLICY = default_capacity_policy>
class MDBX_MSVC_DECLSPEC_EMPTY_BASES buffer;
class env;
class env_managed;
class txn;
class txn_managed;
class cursor;
class cursor_managed;

using txnid = uint64_t;

template <class ALLOCATOR = default_allocator>
using string = ::std::basic_string<char, ::std::char_traits<char>, ALLOCATOR>;
 
using filehandle = ::mdbx_filehandle_t;
#if MDBX_USING_CXX_EXPERIMETAL_FILESYSTEM
#ifdef _MSC_VER
namespace filesystem = ::std::experimental::filesystem::v1;
#else
namespace filesystem = ::std::experimental::filesystem;
#endif
#define MDBX_STD_FILESYSTEM_PATH ::mdbx::filesystem::path
#elif defined(DOXYGEN) ||                                                                                              \
    (defined(__cpp_lib_filesystem) && __cpp_lib_filesystem >= 201703L && defined(__cpp_lib_string_view) &&             \
     __cpp_lib_string_view >= 201606L &&                                                                               \
     (!defined(__MAC_OS_X_VERSION_MIN_REQUIRED) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 101500) &&                       \
     (!defined(__IPHONE_OS_VERSION_MIN_REQUIRED) || __IPHONE_OS_VERSION_MIN_REQUIRED >= 130100)) &&                    \
        (!defined(_MSC_VER) || __cplusplus >= 201703L)
namespace filesystem = ::std::filesystem;
#define MDBX_STD_FILESYSTEM_PATH ::mdbx::filesystem::path
#endif /* MDBX_STD_FILESYSTEM_PATH */
 
#ifdef MDBX_STD_FILESYSTEM_PATH
using path = MDBX_STD_FILESYSTEM_PATH;
#elif defined(_WIN32) || defined(_WIN64)
using path = ::std::wstring;
#else
using path = ::std::string;
#endif /* mdbx::path */
 
#if defined(__SIZEOF_INT128__) || (defined(_INTEGRAL_MAX_BITS) && _INTEGRAL_MAX_BITS >= 128)
#ifndef MDBX_U128_TYPE
#define MDBX_U128_TYPE __uint128_t
#endif /* MDBX_U128_TYPE */
#ifndef MDBX_I128_TYPE
#define MDBX_I128_TYPE __int128_t
#endif /* MDBX_I128_TYPE */
#endif /* __SIZEOF_INT128__ || _INTEGRAL_MAX_BITS >= 128 */
 
#if __cplusplus >= 201103L || defined(DOXYGEN)
using duration = ::std::chrono::duration<unsigned, ::std::ratio<1, 65536>>;
#endif /* Duration for C++11 */


class LIBMDBX_API_TYPE exception_thunk {
  ::std::exception_ptr captured_;
 
public:
  exception_thunk() noexcept = default;
  exception_thunk(const exception_thunk &) = delete;
  exception_thunk(exception_thunk &&) = delete;
  exception_thunk &operator=(const exception_thunk &) = delete;
  exception_thunk &operator=(exception_thunk &&) = delete;
  inline bool is_clean() const noexcept;
  inline void capture() noexcept;
  inline void rethrow_captured() const;
};

class LIBMDBX_API_TYPE error {
  MDBX_error_t code_;
  inline error &operator=(MDBX_error_t error_code) noexcept;
 
public:
  MDBX_CXX11_CONSTEXPR error(MDBX_error_t error_code) noexcept;
  error(const error &) = default;
  error(error &&) = default;
  error &operator=(const error &) = default;
  error &operator=(error &&) = default;
 
  MDBX_CXX11_CONSTEXPR friend bool operator==(const error &a, const error &b) noexcept;
  MDBX_CXX11_CONSTEXPR friend bool operator!=(const error &a, const error &b) noexcept;
 
  MDBX_CXX11_CONSTEXPR bool is_success() const noexcept;
  MDBX_CXX11_CONSTEXPR bool is_result_true() const noexcept;
  MDBX_CXX11_CONSTEXPR bool is_result_false() const noexcept;
  MDBX_CXX11_CONSTEXPR bool is_failure() const noexcept;

  MDBX_CXX11_CONSTEXPR MDBX_error_t code() const noexcept;

  const char *what() const noexcept;

  ::std::string message() const;

  MDBX_CXX11_CONSTEXPR bool is_mdbx_error() const noexcept;
  [[noreturn]] void panic(const char *context_where_when, const char *func_who_what) const noexcept;
  [[noreturn]] void throw_exception() const;
  [[noreturn]] static inline void throw_exception(int error_code);
  inline void throw_on_failure() const;
  inline void success_or_throw() const;
  inline void success_or_throw(const exception_thunk &) const;
  inline void panic_on_failure(const char *context_where, const char *func_who) const noexcept;
  inline void success_or_panic(const char *context_where, const char *func_who) const noexcept;
  static inline void throw_on_nullptr(const void *ptr, MDBX_error_t error_code);
  static inline void success_or_throw(MDBX_error_t error_code);
  static void success_or_throw(int error_code) { success_or_throw(static_cast<MDBX_error_t>(error_code)); }
  static inline void throw_on_failure(int error_code);
  static inline bool boolean_or_throw(int error_code);
  static inline void success_or_throw(int error_code, const exception_thunk &);
  static inline bool boolean_or_throw(int error_code, const exception_thunk &);
  static inline void panic_on_failure(int error_code, const char *context_where, const char *func_who) noexcept;
  static inline void success_or_panic(int error_code, const char *context_where, const char *func_who) noexcept;
};

class LIBMDBX_API_TYPE exception : public ::std::runtime_error {
  using base = ::std::runtime_error;
  ::mdbx::error error_;
 
public:
  exception(const ::mdbx::error &) noexcept;
  exception(const exception &) = default;
  exception(exception &&) = default;
  exception &operator=(const exception &) = default;
  exception &operator=(exception &&) = default;
  virtual ~exception() noexcept;
  const ::mdbx::error error() const noexcept { return error_; }
};

class LIBMDBX_API_TYPE fatal : public exception {
  using base = exception;
 
public:
  fatal(const ::mdbx::error &) noexcept;
  fatal(const exception &src) noexcept : fatal(src.error()) {}
  fatal(exception &&src) noexcept : fatal(src.error()) {}
  fatal(const fatal &src) noexcept : fatal(src.error()) {}
  fatal(fatal &&src) noexcept : fatal(src.error()) {}
  fatal &operator=(fatal &&) = default;
  fatal &operator=(const fatal &) = default;
  virtual ~fatal() noexcept;
};
 
#define MDBX_DECLARE_EXCEPTION(NAME)                                                                                   \
  struct LIBMDBX_API_TYPE NAME : public exception {                                                                    \
    NAME(const ::mdbx::error &);                                                                                       \
    virtual ~NAME() noexcept;                                                                                          \
  }
MDBX_DECLARE_EXCEPTION(bad_map_id);
MDBX_DECLARE_EXCEPTION(bad_transaction);
MDBX_DECLARE_EXCEPTION(bad_value_size);
MDBX_DECLARE_EXCEPTION(db_corrupted);
MDBX_DECLARE_EXCEPTION(db_full);
MDBX_DECLARE_EXCEPTION(db_invalid);
MDBX_DECLARE_EXCEPTION(db_too_large);
MDBX_DECLARE_EXCEPTION(db_unable_extend);
MDBX_DECLARE_EXCEPTION(db_version_mismatch);
MDBX_DECLARE_EXCEPTION(db_wanna_write_for_recovery);
MDBX_DECLARE_EXCEPTION(incompatible_operation);
MDBX_DECLARE_EXCEPTION(internal_page_full);
MDBX_DECLARE_EXCEPTION(internal_problem);
MDBX_DECLARE_EXCEPTION(key_exists);
MDBX_DECLARE_EXCEPTION(key_mismatch);
MDBX_DECLARE_EXCEPTION(max_maps_reached);
MDBX_DECLARE_EXCEPTION(max_readers_reached);
MDBX_DECLARE_EXCEPTION(multivalue);
MDBX_DECLARE_EXCEPTION(no_data);
MDBX_DECLARE_EXCEPTION(not_found);
MDBX_DECLARE_EXCEPTION(operation_not_permitted);
MDBX_DECLARE_EXCEPTION(permission_denied_or_not_writeable);
MDBX_DECLARE_EXCEPTION(reader_slot_busy);
MDBX_DECLARE_EXCEPTION(remote_media);
MDBX_DECLARE_EXCEPTION(something_busy);
MDBX_DECLARE_EXCEPTION(thread_mismatch);
MDBX_DECLARE_EXCEPTION(transaction_full);
MDBX_DECLARE_EXCEPTION(transaction_overlapping);
MDBX_DECLARE_EXCEPTION(duplicated_lck_file);
MDBX_DECLARE_EXCEPTION(dangling_map_id);
MDBX_DECLARE_EXCEPTION(transaction_ousted);
MDBX_DECLARE_EXCEPTION(mvcc_retarded);
#undef MDBX_DECLARE_EXCEPTION
 
[[noreturn]] LIBMDBX_API void throw_too_small_target_buffer();
[[noreturn]] LIBMDBX_API void throw_max_length_exceeded();
[[noreturn]] LIBMDBX_API void throw_out_range();
[[noreturn]] LIBMDBX_API void throw_allocators_mismatch();
[[noreturn]] LIBMDBX_API void throw_bad_value_size();
[[noreturn]] LIBMDBX_API void throw_incomparable_cursors();
 
static MDBX_CXX14_CONSTEXPR size_t check_length(size_t bytes) {
  if (MDBX_UNLIKELY(bytes > size_t(MDBX_MAXDATASIZE)))
    MDBX_CXX20_UNLIKELY throw_max_length_exceeded();
  return bytes;
}
 
static MDBX_CXX14_CONSTEXPR size_t check_length(size_t headroom, size_t payload) {
  return check_length(check_length(headroom) + check_length(payload));
}
 
MDBX_MAYBE_UNUSED static MDBX_CXX14_CONSTEXPR size_t check_length(size_t headroom, size_t payload, size_t tailroom) {
  return check_length(check_length(headroom, payload) + check_length(tailroom));
}

 
//------------------------------------------------------------------------------


struct LIBMDBX_API_TYPE slice : public ::MDBX_val {
 
  enum : size_t { max_length = MDBX_MAXDATASIZE };

  MDBX_CXX11_CONSTEXPR slice() noexcept;

  MDBX_CXX14_CONSTEXPR slice(const void *ptr, size_t bytes);

  MDBX_CXX14_CONSTEXPR slice(const void *begin, const void *end);

  template <size_t SIZE> MDBX_CXX14_CONSTEXPR slice(const char (&text)[SIZE]) : slice(text, SIZE - 1) {
    MDBX_CONSTEXPR_ASSERT(SIZE > 0 && text[SIZE - 1] == '\0');
  }

  explicit MDBX_CXX17_CONSTEXPR slice(const char *c_str);

  template <class CHAR, class T, class A>
  explicit MDBX_CXX20_CONSTEXPR slice(const ::std::basic_string<CHAR, T, A> &str)
      : slice(str.data(), str.length() * sizeof(CHAR)) {}
 
  MDBX_CXX14_CONSTEXPR slice(const MDBX_val &src);
  MDBX_CXX11_CONSTEXPR slice(const slice &) noexcept = default;
  MDBX_CXX14_CONSTEXPR slice(MDBX_val &&src);
  MDBX_CXX14_CONSTEXPR slice(slice &&src) noexcept;
 
#if defined(DOXYGEN) || (defined(__cpp_lib_span) && __cpp_lib_span >= 202002L)
  template <typename POD> MDBX_CXX14_CONSTEXPR slice(const ::std::span<POD> &span) : slice(span.begin(), span.end()) {
    static_assert(::std::is_standard_layout<POD>::value && !::std::is_pointer<POD>::value,
                  "Must be a standard layout type!");
  }
 
  template <typename POD> MDBX_CXX14_CONSTEXPR ::std::span<const POD> as_span() const {
    static_assert(::std::is_standard_layout<POD>::value && !::std::is_pointer<POD>::value,
                  "Must be a standard layout type!");
    if (MDBX_LIKELY(size() % sizeof(POD) == 0))
      MDBX_CXX20_LIKELY
    return ::std::span<const POD>(static_cast<const POD *>(data()), size() / sizeof(POD));
    throw_bad_value_size();
  }
 
  template <typename POD> MDBX_CXX14_CONSTEXPR ::std::span<POD> as_span() {
    static_assert(::std::is_standard_layout<POD>::value && !::std::is_pointer<POD>::value,
                  "Must be a standard layout type!");
    if (MDBX_LIKELY(size() % sizeof(POD) == 0))
      MDBX_CXX20_LIKELY
    return ::std::span<POD>(static_cast<POD *>(data()), size() / sizeof(POD));
    throw_bad_value_size();
  }
 
  MDBX_CXX14_CONSTEXPR ::std::span<const byte> bytes() const { return as_span<const byte>(); }
  MDBX_CXX14_CONSTEXPR ::std::span<byte> bytes() { return as_span<byte>(); }
  MDBX_CXX14_CONSTEXPR ::std::span<const char> chars() const { return as_span<const char>(); }
  MDBX_CXX14_CONSTEXPR ::std::span<char> chars() { return as_span<char>(); }
#endif /* __cpp_lib_span >= 202002L */
 
#if defined(DOXYGEN) || (defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L)
  template <class CHAR, class T>
  MDBX_CXX14_CONSTEXPR slice(const ::std::basic_string_view<CHAR, T> &sv) : slice(sv.data(), sv.data() + sv.length()) {}
 
  template <class CHAR, class T> slice(::std::basic_string_view<CHAR, T> &&sv) : slice(sv) { sv = {}; }
#endif /* __cpp_lib_string_view >= 201606L */
 
  template <size_t SIZE> static MDBX_CXX14_CONSTEXPR slice wrap(const char (&text)[SIZE]) { return slice(text); }
 
  template <typename POD> MDBX_CXX14_CONSTEXPR static slice wrap(const POD &pod) {
    static_assert(::std::is_standard_layout<POD>::value && !::std::is_pointer<POD>::value,
                  "Must be a standard layout type!");
    return slice(&pod, sizeof(pod));
  }
 
  inline slice &assign(const void *ptr, size_t bytes);
  inline slice &assign(const slice &src) noexcept;
  inline slice &assign(const ::MDBX_val &src);
  inline slice &assign(slice &&src) noexcept;
  inline slice &assign(::MDBX_val &&src);
  inline slice &assign(const void *begin, const void *end);
  template <class CHAR, class T, class ALLOCATOR> slice &assign(const ::std::basic_string<CHAR, T, ALLOCATOR> &str) {
    return assign(str.data(), str.length() * sizeof(CHAR));
  }
  inline slice &assign(const char *c_str);
#if defined(DOXYGEN) || (defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L)
  template <class CHAR, class T> slice &assign(const ::std::basic_string_view<CHAR, T> &view) {
    return assign(view.begin(), view.end());
  }
  template <class CHAR, class T> slice &assign(::std::basic_string_view<CHAR, T> &&view) {
    assign(view);
    view = {};
    return *this;
  }
#endif /* __cpp_lib_string_view >= 201606L */
 
  slice &operator=(const slice &) noexcept = default;
  inline slice &operator=(slice &&src) noexcept;
  inline slice &operator=(::MDBX_val &&src);
  operator MDBX_val *() noexcept { return this; }
  operator const MDBX_val *() const noexcept { return this; }
 
#if defined(DOXYGEN) || (defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L)
  template <class CHAR, class T> slice &operator=(const ::std::basic_string_view<CHAR, T> &view) {
    return assign(view);
  }
 
  template <class CHAR, class T> slice &operator=(::std::basic_string_view<CHAR, T> &&view) { return assign(view); }

  template <class CHAR = char, class T = ::std::char_traits<CHAR>>
  MDBX_CXX11_CONSTEXPR ::std::basic_string_view<CHAR, T> string_view() const noexcept {
    static_assert(sizeof(CHAR) == 1, "Must be single byte characters");
    return ::std::basic_string_view<CHAR, T>(char_ptr(), length());
  }

  template <class CHAR, class T>
  MDBX_CXX11_CONSTEXPR explicit operator ::std::basic_string_view<CHAR, T>() const noexcept {
    return this->string_view<CHAR, T>();
  }
#endif /* __cpp_lib_string_view >= 201606L */
 
  template <class CHAR = char, class T = ::std::char_traits<CHAR>, class ALLOCATOR = default_allocator>
  MDBX_CXX20_CONSTEXPR ::std::basic_string<CHAR, T, ALLOCATOR> as_string(const ALLOCATOR &alloc = ALLOCATOR()) const {
    static_assert(sizeof(CHAR) == 1, "Must be single byte characters");
    return ::std::basic_string<CHAR, T, ALLOCATOR>(char_ptr(), length(), alloc);
  }
 
  template <class CHAR, class T, class ALLOCATOR>
  MDBX_CXX20_CONSTEXPR explicit operator ::std::basic_string<CHAR, T, ALLOCATOR>() const {
    return as_string<CHAR, T, ALLOCATOR>();
  }

  template <class ALLOCATOR = default_allocator>
  inline string<ALLOCATOR> as_hex_string(bool uppercase = false, unsigned wrap_width = 0,
                                         const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator>
  inline string<ALLOCATOR> as_base58_string(unsigned wrap_width = 0, const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator>
  inline string<ALLOCATOR> as_base64_string(unsigned wrap_width = 0, const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, class CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> encode_hex(bool uppercase = false, unsigned wrap_width = 0,
                                                       const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, class CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> encode_base58(unsigned wrap_width = 0,
                                                          const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, class CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> encode_base64(unsigned wrap_width = 0,
                                                          const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, class CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> hex_decode(bool ignore_spaces = false,
                                                       const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, class CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> base58_decode(bool ignore_spaces = false,
                                                          const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, class CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> base64_decode(bool ignore_spaces = false,
                                                          const ALLOCATOR &alloc = ALLOCATOR()) const;

  MDBX_NOTHROW_PURE_FUNCTION bool is_printable(bool disable_utf8 = false) const noexcept;

  MDBX_NOTHROW_PURE_FUNCTION inline bool is_hex(bool ignore_spaces = false) const noexcept;

  MDBX_NOTHROW_PURE_FUNCTION inline bool is_base58(bool ignore_spaces = false) const noexcept;

  MDBX_NOTHROW_PURE_FUNCTION inline bool is_base64(bool ignore_spaces = false) const noexcept;
 
#if defined(DOXYGEN) || (defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L)
  template <class CHAR, class T> void swap(::std::basic_string_view<CHAR, T> &view) noexcept {
    static_assert(sizeof(CHAR) == 1, "Must be single byte characters");
    const auto temp = ::std::basic_string_view<CHAR, T>(*this);
    *this = view;
    view = temp;
  }
#endif /* __cpp_lib_string_view >= 201606L */

  MDBX_CXX11_CONSTEXPR const byte *byte_ptr() const noexcept;
  MDBX_CXX11_CONSTEXPR byte *byte_ptr() noexcept;

  MDBX_CXX11_CONSTEXPR const byte *end_byte_ptr() const noexcept;
  MDBX_CXX11_CONSTEXPR byte *end_byte_ptr() noexcept;

  MDBX_CXX11_CONSTEXPR const char *char_ptr() const noexcept;
  MDBX_CXX11_CONSTEXPR char *char_ptr() noexcept;

  MDBX_CXX11_CONSTEXPR const char *end_char_ptr() const noexcept;
  MDBX_CXX11_CONSTEXPR char *end_char_ptr() noexcept;

  MDBX_CXX11_CONSTEXPR const void *data() const noexcept;
  MDBX_CXX11_CONSTEXPR void *data() noexcept;

  MDBX_CXX11_CONSTEXPR const void *end() const noexcept;
  MDBX_CXX11_CONSTEXPR void *end() noexcept;

  MDBX_CXX11_CONSTEXPR size_t length() const noexcept;

  MDBX_CXX14_CONSTEXPR slice &set_length(size_t bytes);

  MDBX_CXX14_CONSTEXPR slice &set_end(const void *ptr);

  MDBX_CXX11_CONSTEXPR bool empty() const noexcept;

  MDBX_CXX11_CONSTEXPR bool is_null() const noexcept;

  MDBX_CXX11_CONSTEXPR size_t size() const noexcept;

  MDBX_CXX11_CONSTEXPR operator bool() const noexcept;

  MDBX_CXX14_CONSTEXPR void invalidate() noexcept;

  MDBX_CXX14_CONSTEXPR void clear() noexcept;

  inline void remove_prefix(size_t n) noexcept;

  inline void remove_suffix(size_t n) noexcept;

  inline void safe_remove_prefix(size_t n);

  inline void safe_remove_suffix(size_t n);

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool starts_with(const slice &prefix) const noexcept;

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool ends_with(const slice &suffix) const noexcept;

  MDBX_CXX11_CONSTEXPR byte operator[](size_t n) const noexcept;

  MDBX_CXX11_CONSTEXPR byte at(size_t n) const;

  MDBX_CXX14_CONSTEXPR slice head(size_t n) const noexcept;

  MDBX_CXX14_CONSTEXPR slice tail(size_t n) const noexcept;

  MDBX_CXX14_CONSTEXPR slice middle(size_t from, size_t n) const noexcept;

  MDBX_CXX14_CONSTEXPR slice safe_head(size_t n) const;

  MDBX_CXX14_CONSTEXPR slice safe_tail(size_t n) const;

  MDBX_CXX14_CONSTEXPR slice safe_middle(size_t from, size_t n) const;

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR size_t hash_value() const noexcept;

  MDBX_NOTHROW_PURE_FUNCTION static MDBX_CXX14_CONSTEXPR intptr_t compare_fast(const slice &a, const slice &b) noexcept;

  MDBX_NOTHROW_PURE_FUNCTION static MDBX_CXX14_CONSTEXPR intptr_t compare_lexicographically(const slice &a,
                                                                                            const slice &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator==(const slice &a, const slice &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator<(const slice &a, const slice &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator>(const slice &a, const slice &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator<=(const slice &a, const slice &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator>=(const slice &a, const slice &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator!=(const slice &a, const slice &b) noexcept;
#if defined(__cpp_impl_three_way_comparison) && __cpp_impl_three_way_comparison >= 201907L
  friend MDBX_CXX14_CONSTEXPR auto operator<=>(const slice &a, const slice &b) noexcept;
#endif /* __cpp_impl_three_way_comparison */

  MDBX_CXX11_CONSTEXPR bool is_valid() const noexcept { return !(iov_base == nullptr && iov_len != 0); }

  MDBX_CXX14_CONSTEXPR static slice invalid() noexcept {
    return slice(/* using special constructor without length checking */ ~size_t(0));
  }

  MDBX_CXX14_CONSTEXPR static slice null() noexcept { return slice(nullptr, size_t(0)); }
 
  template <typename POD> MDBX_CXX14_CONSTEXPR POD as_pod() const {
    static_assert(::std::is_standard_layout<POD>::value && !::std::is_pointer<POD>::value,
                  "Must be a standard layout type!");
    if (MDBX_LIKELY(size() == sizeof(POD)))
      MDBX_CXX20_LIKELY {
        POD r;
        memcpy(&r, data(), sizeof(r));
        return r;
      }
    throw_bad_value_size();
  }
 
#ifdef MDBX_U128_TYPE
  MDBX_CXX14_CONSTEXPR MDBX_U128_TYPE as_uint128() const { return as_pod<MDBX_U128_TYPE>(); }
#endif /* MDBX_U128_TYPE */
  MDBX_CXX14_CONSTEXPR uint64_t as_uint64() const { return as_pod<uint64_t>(); }
  MDBX_CXX14_CONSTEXPR uint32_t as_uint32() const { return as_pod<uint32_t>(); }
  MDBX_CXX14_CONSTEXPR uint16_t as_uint16() const { return as_pod<uint16_t>(); }
  MDBX_CXX14_CONSTEXPR uint8_t as_uint8() const { return as_pod<uint8_t>(); }
 
#ifdef MDBX_I128_TYPE
  MDBX_CXX14_CONSTEXPR MDBX_I128_TYPE as_int128() const { return as_pod<MDBX_I128_TYPE>(); }
#endif /* MDBX_I128_TYPE */
  MDBX_CXX14_CONSTEXPR int64_t as_int64() const { return as_pod<int64_t>(); }
  MDBX_CXX14_CONSTEXPR int32_t as_int32() const { return as_pod<int32_t>(); }
  MDBX_CXX14_CONSTEXPR int16_t as_int16() const { return as_pod<int16_t>(); }
  MDBX_CXX14_CONSTEXPR int8_t as_int8() const { return as_pod<int8_t>(); }
 
#ifdef MDBX_U128_TYPE
  MDBX_U128_TYPE as_uint128_adapt() const;
#endif /* MDBX_U128_TYPE */
  uint64_t as_uint64_adapt() const;
  uint32_t as_uint32_adapt() const;
  uint16_t as_uint16_adapt() const;
  uint8_t as_uint8_adapt() const;
 
#ifdef MDBX_I128_TYPE
  MDBX_I128_TYPE as_int128_adapt() const;
#endif /* MDBX_I128_TYPE */
  int64_t as_int64_adapt() const;
  int32_t as_int32_adapt() const;
  int16_t as_int16_adapt() const;
  int8_t as_int8_adapt() const;
 
protected:
  MDBX_CXX11_CONSTEXPR slice(size_t invalid_length) noexcept : ::MDBX_val({nullptr, invalid_length}) {}
};

struct value_result {
  slice value;
  bool done;
  value_result(const slice &value, bool done) noexcept : value(value), done(done) {}
  value_result(const value_result &) noexcept = default;
  value_result &operator=(const value_result &) noexcept = default;
  MDBX_CXX14_CONSTEXPR operator bool() const noexcept {
    assert(!done || bool(value));
    return done;
  }
};

struct pair {
  using stl_pair = std::pair<slice, slice>;
  slice key, value;
  MDBX_CXX11_CONSTEXPR pair(const slice &key, const slice &value) noexcept : key(key), value(value) {}
  MDBX_CXX11_CONSTEXPR pair(const stl_pair &couple) noexcept : key(couple.first), value(couple.second) {}
  MDBX_CXX11_CONSTEXPR operator stl_pair() const noexcept { return stl_pair(key, value); }
  pair(const pair &) noexcept = default;
  pair &operator=(const pair &) noexcept = default;
  pair &operator=(pair &&couple) {
    key.assign(std::move(couple.key));
    value.assign(std::move(couple.value));
    return *this;
  }
  MDBX_CXX14_CONSTEXPR operator bool() const noexcept {
    assert(bool(key) == bool(value));
    return key;
  }
  MDBX_CXX14_CONSTEXPR static pair invalid() noexcept { return pair(slice::invalid(), slice::invalid()); }
 
  pair &operator=(const stl_pair &couple) {
    key.assign(couple.first);
    value.assign(couple.second);
    return *this;
  }
  pair &operator=(stl_pair &&couple) {
    key.assign(std::move(couple.first));
    value.assign(std::move(couple.second));
    return *this;
  }

  MDBX_NOTHROW_PURE_FUNCTION static MDBX_CXX14_CONSTEXPR intptr_t compare_fast(const pair &a, const pair &b) noexcept;

  MDBX_NOTHROW_PURE_FUNCTION static MDBX_CXX14_CONSTEXPR intptr_t compare_lexicographically(const pair &a,
                                                                                            const pair &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator==(const pair &a, const pair &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator<(const pair &a, const pair &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator>(const pair &a, const pair &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator<=(const pair &a, const pair &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator>=(const pair &a, const pair &b) noexcept;
  friend MDBX_CXX14_CONSTEXPR bool operator!=(const pair &a, const pair &b) noexcept;
#if defined(__cpp_impl_three_way_comparison) && __cpp_impl_three_way_comparison >= 201907L
  friend MDBX_CXX14_CONSTEXPR auto operator<=>(const pair &a, const pair &b) noexcept;
#endif /* __cpp_impl_three_way_comparison */
};

struct pair_result : public pair {
  bool done;
  MDBX_CXX11_CONSTEXPR pair_result() noexcept : pair(pair::invalid()), done(false) {}
  MDBX_CXX11_CONSTEXPR pair_result(const slice &key, const slice &value, bool done) noexcept
      : pair(key, value), done(done) {}
  pair_result(const pair_result &) noexcept = default;
  pair_result &operator=(const pair_result &) noexcept = default;
  MDBX_CXX14_CONSTEXPR operator bool() const noexcept {
    assert(!done || (bool(key) && bool(value)));
    return done;
  }
};
 
#if MDBX_HAVE_CXX20_CONCEPTS || defined(DOXYGEN)

template <typename T>
concept MutableByteProducer = requires(T a, char array[42]) {
  { a.is_empty() } -> std::same_as<bool>;
  { a.envisage_result_length() } -> std::same_as<size_t>;
  { a.write_bytes(&array[0], size_t(42)) } -> std::same_as<char *>;
};

template <typename T>
concept ImmutableByteProducer = requires(const T &a, char array[42]) {
  { a.is_empty() } -> std::same_as<bool>;
  { a.envisage_result_length() } -> std::same_as<size_t>;
  { a.write_bytes(&array[0], size_t(42)) } -> std::same_as<char *>;
};

template <typename T>
concept SliceTranscoder = ImmutableByteProducer<T> && requires(const slice &source, const T &a) {
  T(source);
  { a.is_erroneous() } -> std::same_as<bool>;
};
 
#endif /* MDBX_HAVE_CXX20_CONCEPTS */

struct LIBMDBX_API to_hex {
  const slice source;
  const bool uppercase = false;
  const unsigned wrap_width = 0;
  MDBX_CXX11_CONSTEXPR to_hex(const slice &source, bool uppercase = false, unsigned wrap_width = 0) noexcept
      : source(source), uppercase(uppercase), wrap_width(wrap_width) {
    MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(SliceTranscoder, to_hex);
  }

  template <class ALLOCATOR = default_allocator>
  inline string<ALLOCATOR> as_string(const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, typename CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> as_buffer(const ALLOCATOR &alloc = ALLOCATOR()) const;

  MDBX_CXX11_CONSTEXPR size_t envisage_result_length() const noexcept {
    const size_t bytes = source.length() << 1;
    return wrap_width ? bytes + bytes / wrap_width : bytes;
  }

  char *write_bytes(char *dest, size_t dest_size) const;

  ::std::ostream &output(::std::ostream &out) const;

  bool is_empty() const noexcept { return source.empty(); }

  bool is_erroneous() const noexcept { return false; }
};

struct LIBMDBX_API to_base58 {
  const slice source;
  const unsigned wrap_width = 0;
  MDBX_CXX11_CONSTEXPR
  to_base58(const slice &source, unsigned wrap_width = 0) noexcept : source(source), wrap_width(wrap_width) {
    MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(SliceTranscoder, to_base58);
  }

  template <class ALLOCATOR = default_allocator>
  inline string<ALLOCATOR> as_string(const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, typename CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> as_buffer(const ALLOCATOR &alloc = ALLOCATOR()) const;

  MDBX_CXX11_CONSTEXPR size_t envisage_result_length() const noexcept {
    const size_t bytes = (source.length() * 11 + 7) / 8;
    return wrap_width ? bytes + bytes / wrap_width : bytes;
  }

  char *write_bytes(char *dest, size_t dest_size) const;

  ::std::ostream &output(::std::ostream &out) const;

  bool is_empty() const noexcept { return source.empty(); }

  bool is_erroneous() const noexcept { return false; }
};

struct LIBMDBX_API to_base64 {
  const slice source;
  const unsigned wrap_width = 0;
  MDBX_CXX11_CONSTEXPR
  to_base64(const slice &source, unsigned wrap_width = 0) noexcept : source(source), wrap_width(wrap_width) {
    MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(SliceTranscoder, to_base64);
  }

  template <class ALLOCATOR = default_allocator>
  inline string<ALLOCATOR> as_string(const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, typename CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> as_buffer(const ALLOCATOR &alloc = ALLOCATOR()) const;

  MDBX_CXX11_CONSTEXPR size_t envisage_result_length() const noexcept {
    const size_t bytes = (source.length() + 2) / 3 * 4;
    return wrap_width ? bytes + bytes / wrap_width : bytes;
  }

  char *write_bytes(char *dest, size_t dest_size) const;

  ::std::ostream &output(::std::ostream &out) const;

  bool is_empty() const noexcept { return source.empty(); }

  bool is_erroneous() const noexcept { return false; }
};

struct LIBMDBX_API from_hex {
  const slice source;
  const bool ignore_spaces = false;
  MDBX_CXX11_CONSTEXPR from_hex(const slice &source, bool ignore_spaces = false) noexcept
      : source(source), ignore_spaces(ignore_spaces) {
    MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(SliceTranscoder, from_hex);
  }

  template <class ALLOCATOR = default_allocator>
  inline string<ALLOCATOR> as_string(const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, typename CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> as_buffer(const ALLOCATOR &alloc = ALLOCATOR()) const;

  MDBX_CXX11_CONSTEXPR size_t envisage_result_length() const noexcept { return source.length() >> 1; }

  char *write_bytes(char *dest, size_t dest_size) const;

  bool is_empty() const noexcept { return source.empty(); }

  bool is_erroneous() const noexcept;
};

struct LIBMDBX_API from_base58 {
  const slice source;
  const bool ignore_spaces = false;
  MDBX_CXX11_CONSTEXPR from_base58(const slice &source, bool ignore_spaces = false) noexcept
      : source(source), ignore_spaces(ignore_spaces) {
    MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(SliceTranscoder, from_base58);
  }

  template <class ALLOCATOR = default_allocator>
  inline string<ALLOCATOR> as_string(const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, typename CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> as_buffer(const ALLOCATOR &alloc = ALLOCATOR()) const;

  MDBX_CXX11_CONSTEXPR size_t envisage_result_length() const noexcept {
    return source.length() /* могут быть все нули кодируемые один-к-одному */;
  }

  char *write_bytes(char *dest, size_t dest_size) const;

  bool is_empty() const noexcept { return source.empty(); }

  bool is_erroneous() const noexcept;
};

struct LIBMDBX_API from_base64 {
  const slice source;
  const bool ignore_spaces = false;
  MDBX_CXX11_CONSTEXPR from_base64(const slice &source, bool ignore_spaces = false) noexcept
      : source(source), ignore_spaces(ignore_spaces) {
    MDBX_ASSERT_CXX20_CONCEPT_SATISFIED(SliceTranscoder, from_base64);
  }

  template <class ALLOCATOR = default_allocator>
  inline string<ALLOCATOR> as_string(const ALLOCATOR &alloc = ALLOCATOR()) const;

  template <class ALLOCATOR = default_allocator, typename CAPACITY_POLICY = default_capacity_policy>
  inline buffer<ALLOCATOR, CAPACITY_POLICY> as_buffer(const ALLOCATOR &alloc = ALLOCATOR()) const;

  MDBX_CXX11_CONSTEXPR size_t envisage_result_length() const noexcept { return (source.length() + 3) / 4 * 3; }

  char *write_bytes(char *dest, size_t dest_size) const;

  bool is_empty() const noexcept { return source.empty(); }

  bool is_erroneous() const noexcept;
};
 
namespace allocation_aware_details {
 
template <typename A> constexpr bool allocator_is_always_equal() noexcept {
#if defined(__cpp_lib_allocator_traits_is_always_equal) && __cpp_lib_allocator_traits_is_always_equal >= 201411L
  return ::std::allocator_traits<A>::is_always_equal::value;
#else
  return ::std::is_empty<A>::value;
#endif /* __cpp_lib_allocator_traits_is_always_equal */
}
 
template <typename T, typename A = typename T::allocator_type,
          bool PoCMA = ::std::allocator_traits<A>::propagate_on_container_move_assignment::value>
struct move_assign_alloc;
 
template <typename T, typename A> struct move_assign_alloc<T, A, false> {
  static constexpr bool is_nothrow() noexcept { return allocator_is_always_equal<A>(); }
  static MDBX_CXX20_CONSTEXPR bool is_moveable(T *target, T &source) noexcept {
    return allocator_is_always_equal<A>() || target->get_allocator() == source.get_allocator();
  }
  static MDBX_CXX20_CONSTEXPR void propagate(T *, T &) noexcept {}
};
 
template <typename T, typename A> struct move_assign_alloc<T, A, true> {
  static constexpr bool is_nothrow() noexcept {
    return allocator_is_always_equal<A>() || ::std::is_nothrow_move_assignable<A>::value;
  }
  static constexpr bool is_moveable(T *, T &) noexcept { return true; }
  static MDBX_CXX20_CONSTEXPR void propagate(T *target, T &source) noexcept {
    target->get_allocator() = ::std::move(source.get_allocator());
  }
};
 
template <typename T, typename A = typename T::allocator_type,
          bool PoCCA = ::std::allocator_traits<A>::propagate_on_container_copy_assignment::value>
struct copy_assign_alloc;
 
template <typename T, typename A> struct copy_assign_alloc<T, A, false> {
  static constexpr bool is_nothrow() noexcept { return false; }
  static MDBX_CXX20_CONSTEXPR void propagate(T *, const T &) noexcept {}
};
 
template <typename T, typename A> struct copy_assign_alloc<T, A, true> {
  static constexpr bool is_nothrow() noexcept {
    return allocator_is_always_equal<A>() || ::std::is_nothrow_copy_assignable<A>::value;
  }
  static MDBX_CXX20_CONSTEXPR void propagate(T *target, const T &source) noexcept(is_nothrow()) {
    if MDBX_IF_CONSTEXPR (!allocator_is_always_equal<A>()) {
      if (MDBX_UNLIKELY(target->get_allocator() != source.get_allocator()))
        MDBX_CXX20_UNLIKELY target->get_allocator() =
            ::std::allocator_traits<A>::select_on_container_copy_construction(source.get_allocator());
    } else {
      /* gag for buggy compilers */
      (void)target;
      (void)source;
    }
  }
};
 
template <typename T, typename A = typename T::allocator_type,
          bool PoCS = ::std::allocator_traits<A>::propagate_on_container_swap::value>
struct swap_alloc;
 
template <typename T, typename A> struct swap_alloc<T, A, false> {
  static constexpr bool is_nothrow() noexcept { return allocator_is_always_equal<A>(); }
  static MDBX_CXX20_CONSTEXPR void propagate(T &left, T &right) noexcept(is_nothrow()) {
    if MDBX_IF_CONSTEXPR (!allocator_is_always_equal<A>()) {
      if (MDBX_UNLIKELY(left.get_allocator() != right.get_allocator()))
        MDBX_CXX20_UNLIKELY throw_allocators_mismatch();
    } else {
      /* gag for buggy compilers */
      (void)left;
      (void)right;
    }
  }
};
 
template <typename T, typename A> struct swap_alloc<T, A, true> {
  static constexpr bool is_nothrow() noexcept {
    return allocator_is_always_equal<A>() ||
#if defined(__cpp_lib_is_swappable) && __cpp_lib_is_swappable >= 201603L
           ::std::is_nothrow_swappable<A>() ||
#endif /* __cpp_lib_is_swappable >= 201603L */
           (::std::is_nothrow_move_constructible<A>::value && ::std::is_nothrow_move_assignable<A>::value);
  }
  static MDBX_CXX20_CONSTEXPR void propagate(T &left, T &right) noexcept(is_nothrow()) {
    if MDBX_IF_CONSTEXPR (!allocator_is_always_equal<A>()) {
      if (MDBX_UNLIKELY(left.get_allocator() != right.get_allocator()))
        MDBX_CXX20_UNLIKELY ::std::swap(left.get_allocator(), right.get_allocator());
    } else {
      /* gag for buggy compilers */
      (void)left;
      (void)right;
    }
  }
};
 
} // namespace allocation_aware_details
 
struct default_capacity_policy {
  enum : size_t {
    extra_inplace_storage = 0,
    inplace_storage_size_rounding = 16,
    pettiness_threshold = 64,
    max_reserve = 65536
  };
 
  static MDBX_CXX11_CONSTEXPR size_t round(const size_t value) {
    static_assert((pettiness_threshold & (pettiness_threshold - 1)) == 0, "pettiness_threshold must be a power of 2");
    static_assert(pettiness_threshold % 2 == 0, "pettiness_threshold must be even");
    static_assert(pettiness_threshold >= sizeof(uint64_t), "pettiness_threshold must be > 7");
    constexpr const auto pettiness_mask = ~size_t(pettiness_threshold - 1);
    return (value + pettiness_threshold - 1) & pettiness_mask;
  }
 
  static MDBX_CXX11_CONSTEXPR size_t advise(const size_t current, const size_t wanna, const size_t inplace) {
    static_assert(max_reserve % pettiness_threshold == 0, "max_reserve must be a multiple of pettiness_threshold");
    static_assert(max_reserve / 3 > pettiness_threshold, "max_reserve must be > pettiness_threshold * 3");
 
    if (wanna <= inplace && (current <= inplace || current >= std::max(inplace + inplace, size_t(pettiness_threshold))))
      return inplace;
 
    if (wanna > current)
      /* doubling capacity, but don't made reserve more than max_reserve */
      return round(wanna + ::std::min(size_t(max_reserve), current));
 
    if (current - wanna >
        /* shrink if reserve will more than half of current or max_reserve,
         * but not less than pettiness_threshold */
        ::std::min(wanna + pettiness_threshold, size_t(max_reserve)))
      return round(wanna);
 
    /* keep unchanged */
    return current;
  }
};

struct buffer_tag {};

template <class ALLOCATOR, typename CAPACITY_POLICY>
class MDBX_MSVC_DECLSPEC_EMPTY_BASES buffer : public slice, public buffer_tag {
public:
  using inherited = slice;
#if !defined(_MSC_VER) || _MSC_VER > 1900
  using allocator_type = typename ::std::allocator_traits<ALLOCATOR>::template rebind_alloc<uint64_t>;
#else
  using allocator_type = typename ALLOCATOR::template rebind<uint64_t>::other;
#endif /* MSVC is mad */
  using allocator_traits = ::std::allocator_traits<allocator_type>;
  using reservation_policy = CAPACITY_POLICY;
  enum : size_t {
    max_length = MDBX_MAXDATASIZE,
    max_capacity = (max_length / 3u * 4u + 1023u) & ~size_t(1023),
    extra_inplace_storage = reservation_policy::extra_inplace_storage,
    inplace_storage_size_rounding =
        (alignof(max_align_t) * 2 > size_t(reservation_policy::inplace_storage_size_rounding))
            ? alignof(max_align_t) * 2
            : size_t(reservation_policy::inplace_storage_size_rounding),
    pettiness_threshold = reservation_policy::pettiness_threshold
  };
 
private:
  friend class txn;
  struct silo /* Empty Base Class Optimization */ : public allocator_type {
    MDBX_CXX20_CONSTEXPR const allocator_type &get_allocator() const noexcept { return *this; }
    MDBX_CXX20_CONSTEXPR allocator_type &get_allocator() noexcept { return *this; }
 
    using allocator_pointer = typename allocator_traits::pointer;
    using allocator_const_pointer = typename allocator_traits::const_pointer;
 
    MDBX_CXX20_CONSTEXPR ::std::pair<allocator_pointer, size_t> allocate_storage(size_t bytes) {
      assert(bytes >= sizeof(bin));
      constexpr size_t unit = sizeof(typename allocator_type::value_type);
      static_assert((unit & (unit - 1)) == 0, "size of ALLOCATOR::value_type should be a power of 2");
      static_assert(unit > 0, "size of ALLOCATOR::value_type must be > 0");
      const size_t n = (bytes + unit - 1) / unit;
      return ::std::make_pair(allocator_traits::allocate(get_allocator(), n), n * unit);
    }
 
    MDBX_CXX20_CONSTEXPR void deallocate_storage(allocator_pointer ptr, size_t bytes) {
      constexpr size_t unit = sizeof(typename allocator_type::value_type);
      assert(ptr && bytes >= sizeof(bin) && bytes >= unit && bytes % unit == 0);
      allocator_traits::deallocate(get_allocator(), ptr, bytes / unit);
    }
 
    MDBX_CXX20_CONSTEXPR ::std::pair<allocator_pointer, size_t> provide_storage(size_t bytes) {
      const size_t capacity = bin::advise_capacity(0, bytes);
      return bin::is_suitable_for_inplace(capacity) ? ::std::pair<allocator_pointer, size_t>(nullptr, capacity)
                                                    : allocate_storage(capacity);
    }
 
    static MDBX_CXX17_CONSTEXPR void *to_address(allocator_pointer ptr) noexcept {
#if defined(__cpp_lib_to_address) && __cpp_lib_to_address >= 201711L
      return static_cast<void *>(::std::to_address(ptr));
#else
      return static_cast<void *>(::std::addressof(*ptr));
#endif /* __cpp_lib_to_address */
    }
 
    static MDBX_CXX17_CONSTEXPR const void *to_address(allocator_const_pointer ptr) noexcept {
#if defined(__cpp_lib_to_address) && __cpp_lib_to_address >= 201711L
      return static_cast<const void *>(::std::to_address(ptr));
#else
      return static_cast<const void *>(::std::addressof(*ptr));
#endif /* __cpp_lib_to_address */
    }
 
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable : 4324) /* structure was padded due to alignment specifier */
#endif                          /* _MSC_VER */
 
    union alignas(max_align_t) bin {
      struct stub_allocated_holder /* используется только для вычисления (минимального необходимого) размера,
                                      с учетом выравнивания */
      {
        allocator_pointer stub_ptr_;
        size_t stub_capacity_bytes_;
      };
 
      enum : byte { lastbyte_poison = 0, lastbyte_inplace_signature = byte(~byte(lastbyte_poison)) };
      enum : size_t {
        inplace_signature_limit = size_t(lastbyte_inplace_signature)
                                  << (sizeof(size_t /* allocated::capacity_bytes_ */) - 1) * CHAR_BIT,
        inplace_size_rounding = size_t(inplace_storage_size_rounding) - 1,
        inplace_size =
            (sizeof(stub_allocated_holder) + extra_inplace_storage + inplace_size_rounding) & ~inplace_size_rounding
      };
 
      struct capacity_holder {
        byte pad_[inplace_size - sizeof(allocator_pointer)];
        size_t bytes_;
      };
 
      struct inplace_flag_holder {
        byte buffer_[inplace_size - sizeof(byte)];
        byte lastbyte_;
        MDBX_CXX11_CONSTEXPR inplace_flag_holder(byte signature) : lastbyte_(signature) {};
      };
 
      allocator_pointer allocated_ptr_;
      capacity_holder capacity_;
      inplace_flag_holder inplace_;
 
      static constexpr size_t inplace_capacity() noexcept { return sizeof(inplace_flag_holder::buffer_); }
      static constexpr bool is_suitable_for_inplace(size_t capacity_bytes) noexcept {
        static_assert((size_t(reservation_policy::inplace_storage_size_rounding) &
                       (size_t(reservation_policy::inplace_storage_size_rounding) - 1)) == 0,
                      "CAPACITY_POLICY::inplace_storage_size_rounding must be power of 2");
        static_assert(sizeof(bin) == sizeof(inplace_) && sizeof(bin) == sizeof(capacity_), "WTF?");
        return capacity_bytes <= inplace_capacity();
      }
 
      constexpr bool is_inplace() const noexcept {
        static_assert(size_t(inplace_signature_limit) > size_t(max_capacity), "WTF?");
        static_assert(std::numeric_limits<size_t>::max() - (std::numeric_limits<size_t>::max() >> CHAR_BIT) ==
                          inplace_signature_limit,
                      "WTF?");
        return inplace_.lastbyte_ == lastbyte_inplace_signature;
      }
      constexpr bool is_allocated() const noexcept { return !is_inplace(); }
 
      template <bool destroy_ptr> MDBX_CXX17_CONSTEXPR byte *make_inplace() noexcept {
        if (destroy_ptr) {
          MDBX_CONSTEXPR_ASSERT(is_allocated());
          /* properly destroy allocator::pointer */
          allocated_ptr_.~allocator_pointer();
        }
        inplace_.lastbyte_ = lastbyte_inplace_signature;
        MDBX_CONSTEXPR_ASSERT(is_inplace() && address() == inplace_.buffer_ && is_suitable_for_inplace(capacity()));
        return address();
      }
 
      template <bool construct_ptr>
      MDBX_CXX17_CONSTEXPR byte *make_allocated(const ::std::pair<allocator_pointer, size_t> &pair) noexcept {
        MDBX_CONSTEXPR_ASSERT(inplace_signature_limit > pair.second);
        if (construct_ptr) {
          MDBX_CONSTEXPR_ASSERT(is_inplace());
          new (&allocated_ptr_) allocator_pointer(pair.first);
        } else {
          MDBX_CONSTEXPR_ASSERT(is_allocated());
          allocated_ptr_ = pair.first;
        }
        capacity_.bytes_ = pair.second;
        MDBX_CONSTEXPR_ASSERT(is_allocated() && address() == to_address(pair.first) && capacity() == pair.second);
        return address();
      }
 
      MDBX_CXX11_CONSTEXPR bin() noexcept : inplace_(lastbyte_inplace_signature) {
        if (::std::is_trivial<allocator_pointer>::value)
          /* workaround for "uninitialized" warning from some compilers */
          memset(&allocated_ptr_, 0, sizeof(allocated_ptr_));
      }
 
      static MDBX_CXX20_CONSTEXPR size_t advise_capacity(const size_t current, const size_t wanna) {
        if (MDBX_UNLIKELY(wanna > max_capacity))
          MDBX_CXX20_UNLIKELY throw_max_length_exceeded();
 
        const size_t advised = reservation_policy::advise(current, wanna, inplace_capacity());
        assert(advised >= wanna);
        return ::std::min(size_t(max_capacity), ::std::max(inplace_capacity(), advised));
      }
 
      constexpr bool is_inplace(const void *ptr) const noexcept {
        return size_t(static_cast<const byte *>(ptr) - inplace_.buffer_) < inplace_capacity();
      }
 
      constexpr const byte *address() const noexcept {
        return is_inplace() ? inplace_.buffer_ : static_cast<const byte *>(to_address(allocated_ptr_));
      }
      MDBX_CXX17_CONSTEXPR byte *address() noexcept {
        return is_inplace() ? inplace_.buffer_ : static_cast<byte *>(to_address(allocated_ptr_));
      }
      constexpr size_t capacity() const noexcept { return is_inplace() ? inplace_capacity() : capacity_.bytes_; }
    } bin_;
 
#ifdef _MSC_VER
#pragma warning(pop)
#endif /* _MSC_VER */
 
    constexpr bool is_inplace(const void *ptr) const noexcept { return bin_.is_inplace(ptr); }
 
    MDBX_CXX20_CONSTEXPR void release() noexcept {
      if (bin_.is_allocated()) {
        deallocate_storage(bin_.allocated_ptr_, bin_.capacity_.bytes_);
        /* properly destroy allocator::pointer */
        bin_.allocated_ptr_.~allocator_pointer();
        bin_.inplace_.lastbyte_ = bin::lastbyte_inplace_signature;
      }
    }
 
    template <bool external_content>
    MDBX_CXX20_CONSTEXPR void *reshape(const size_t wanna_capacity, const size_t wanna_headroom,
                                       const void *const content, const size_t length) {
      assert(wanna_capacity >= wanna_headroom + length);
      const size_t old_capacity = bin_.capacity();
      const size_t new_capacity = bin::advise_capacity(old_capacity, wanna_capacity);
      if (MDBX_LIKELY(new_capacity == old_capacity))
        MDBX_CXX20_LIKELY {
          assert(bin_.is_inplace() == bin::is_suitable_for_inplace(new_capacity));
          byte *const new_place = bin_.address() + wanna_headroom;
          if (MDBX_LIKELY(length))
            MDBX_CXX20_LIKELY {
              if (external_content)
                memcpy(new_place, content, length);
              else {
                const size_t old_headroom = bin_.address() - static_cast<const byte *>(content);
                assert(old_capacity >= old_headroom + length);
                if (MDBX_UNLIKELY(old_headroom != wanna_headroom))
                  MDBX_CXX20_UNLIKELY ::std::memmove(new_place, content, length);
              }
            }
          return new_place;
        }
 
      if (bin::is_suitable_for_inplace(new_capacity)) {
        assert(bin_.is_allocated());
        const auto old_allocated = ::std::move(bin_.allocated_ptr_);
        byte *const new_place = bin_.template make_inplace<true>() + wanna_headroom;
        if (MDBX_LIKELY(length))
          MDBX_CXX20_LIKELY memcpy(new_place, content, length);
        deallocate_storage(old_allocated, old_capacity);
        return new_place;
      }
 
      if (bin_.is_inplace()) {
        const auto pair = allocate_storage(new_capacity);
        assert(pair.second >= new_capacity);
        byte *const new_place = static_cast<byte *>(to_address(pair.first)) + wanna_headroom;
        if (MDBX_LIKELY(length))
          MDBX_CXX20_LIKELY memcpy(new_place, content, length);
        bin_.template make_allocated<true>(pair);
        return new_place;
      }
 
      const auto old_allocated = ::std::move(bin_.allocated_ptr_);
      if (external_content)
        deallocate_storage(old_allocated, old_capacity);
      const auto pair = allocate_storage(new_capacity);
      assert(pair.second >= new_capacity);
      byte *const new_place = bin_.template make_allocated<false>(pair) + wanna_headroom;
      if (MDBX_LIKELY(length))
        MDBX_CXX20_LIKELY memcpy(new_place, content, length);
      if (!external_content)
        deallocate_storage(old_allocated, old_capacity);
      return new_place;
    }
 
    MDBX_CXX20_CONSTEXPR const byte *get(size_t offset = 0) const noexcept {
      assert(capacity() >= offset);
      return bin_.address() + offset;
    }
    MDBX_CXX20_CONSTEXPR byte *get(size_t offset = 0) noexcept {
      assert(capacity() >= offset);
      return bin_.address() + offset;
    }
    MDBX_CXX20_CONSTEXPR byte *put(size_t offset, const void *ptr, size_t length) {
      assert(capacity() >= offset + length);
      return static_cast<byte *>(memcpy(get(offset), ptr, length));
    }
 
    //--------------------------------------------------------------------------
 
    MDBX_CXX20_CONSTEXPR silo(const allocator_type &alloc = allocator_type()) noexcept : allocator_type(alloc) {}
    MDBX_CXX20_CONSTEXPR silo(size_t capacity, const allocator_type &alloc = allocator_type()) : silo(alloc) {
      if (!bin::is_suitable_for_inplace(capacity))
        bin_.template make_allocated<true>(provide_storage(capacity));
    }
 
    silo(silo &&other) = delete;
    MDBX_CXX20_CONSTEXPR
    silo(silo &&other, bool is_reference = false) noexcept(::std::is_nothrow_move_constructible<allocator_type>::value)
        : allocator_type(::std::move(other.get_allocator())) {
      if (!is_reference) {
        if (other.bin_.is_inplace()) {
          memcpy(&bin_, &other.bin_, sizeof(bin));
          MDBX_CONSTEXPR_ASSERT(bin_.is_inplace());
        } else {
          new (&bin_.allocated_ptr_) allocator_pointer(::std::move(other.bin_.allocated_ptr_));
          bin_.capacity_.bytes_ = other.bin_.capacity_.bytes_;
          /* properly destroy allocator::pointer.
           *
           * CoverityScan issues an erroneous warning here about using an uninitialized object. Which is not true,
           * since in C++ (unlike Rust) an object remains initialized after a move-assignment operation; Moreover,
           * a destructor will be called for such an object (this is explicitly stated in all C++ standards, starting
           * from the 11th). */
          /* coverity[use_after_move] */
          other.bin_.allocated_ptr_.~allocator_pointer();
          other.bin_.inplace_.lastbyte_ = bin::lastbyte_inplace_signature;
          MDBX_CONSTEXPR_ASSERT(bin_.is_allocated() && other.bin_.is_inplace());
        }
      }
    }
 
    MDBX_CXX17_CONSTEXPR bool move(silo &&other) noexcept {
      if (other.bin_.is_inplace()) {
        memcpy(&bin_, &other.bin_, sizeof(bin));
        MDBX_CONSTEXPR_ASSERT(bin_.is_inplace());
        return /* buffer's slice fixup is needed */ true;
      }
      new (&bin_.allocated_ptr_) allocator_pointer(::std::move(other.bin_.allocated_ptr_));
      bin_.capacity_.bytes_ = other.bin_.capacity_.bytes_;
      /* properly destroy allocator::pointer.
       *
       * CoverityScan issues an erroneous warning here about using an uninitialized object. Which is not true,
       * since in C++ (unlike Rust) an object remains initialized after a move-assignment operation; Moreover,
       * a destructor will be called for such an object (this is explicitly stated in all C++ standards, starting
       * from the 11th). */
      /* coverity[use_after_move] */
      other.bin_.allocated_ptr_.~allocator_pointer();
      other.bin_.inplace_.lastbyte_ = bin::lastbyte_inplace_signature;
      MDBX_CONSTEXPR_ASSERT(bin_.is_allocated() && other.bin_.is_inplace());
      return false;
    }
 
    MDBX_CXX17_CONSTEXPR bool assign_move(silo &&other, bool is_reference) noexcept {
      release();
      if (!allocation_aware_details::move_assign_alloc<silo, allocator_type>::is_moveable(this, other))
        allocation_aware_details::move_assign_alloc<silo, allocator_type>::propagate(this, other);
      return is_reference ? false : move(std::move(other));
    }
 
    static MDBX_CXX20_CONSTEXPR std::pair<bool, bool>
    exchange(silo &left, const bool left_is_reference, silo &right, const bool right_is_reference) noexcept(
        allocation_aware_details::swap_alloc<silo, allocator_type>::is_nothrow()) {
      allocation_aware_details::swap_alloc<silo, allocator_type>::propagate(left, right);
      bool left_need_fixup = false, right_need_fixup = false;
      if (left_is_reference || right_is_reference) {
        left_need_fixup = !right_is_reference && left.move(std::move(right));
        right_need_fixup = !left_is_reference && right.move(std::move(left));
      } else {
        silo temp(std::move(left), false);
        left_need_fixup = left.move(std::move(right));
        right_need_fixup = right.move(std::move(temp));
      }
      return std::make_pair(left_need_fixup, right_need_fixup);
    }
 
    MDBX_CXX20_CONSTEXPR silo(size_t capacity, size_t headroom, const void *ptr, size_t length,
                              const allocator_type &alloc = allocator_type())
        : silo(capacity, alloc) {
      assert(capacity >= headroom + length);
      if (length)
        put(headroom, ptr, length);
    }
 
    MDBX_CXX20_CONSTEXPR silo(const void *ptr, size_t length, const allocator_type &alloc = allocator_type())
        : silo(length, 0, ptr, length, alloc) {}
 
    ~silo() { release(); }
 
    //--------------------------------------------------------------------------
 
    MDBX_CXX20_CONSTEXPR void *assign(size_t headroom, const void *ptr, size_t length, size_t tailroom) {
      return reshape<true>(headroom + length + tailroom, headroom, ptr, length);
    }
 
    MDBX_CXX20_CONSTEXPR void *assign(const void *ptr, size_t length) { return assign(0, ptr, length, 0); }
 
    MDBX_CXX20_CONSTEXPR void *clear() { return reshape<true>(0, 0, nullptr, 0); }
    MDBX_CXX20_CONSTEXPR void *clear_and_reserve(size_t whole_capacity, size_t headroom) {
      return reshape<false>(whole_capacity, headroom, nullptr, 0);
    }
 
    MDBX_CXX20_CONSTEXPR void resize(size_t capacity, size_t headroom, slice &content) {
      content.iov_base = reshape<false>(capacity, headroom, content.iov_base, content.iov_len);
    }
 
    MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX11_CONSTEXPR size_t capacity() const noexcept { return bin_.capacity(); }
    MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX11_CONSTEXPR const void *data(size_t offset = 0) const noexcept {
      return get(offset);
    }
    MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX11_CONSTEXPR void *data(size_t offset = 0) noexcept { return get(offset); }
  };
 
  MDBX_CXX14_CONSTEXPR void fixup_import(const typename silo::bin &src) noexcept {
    auto ptr = inherited::byte_ptr();
    if (src.is_inplace(ptr)) {
      MDBX_CONSTEXPR_ASSERT(silo_.bin_.is_inplace());
      intptr_t offset = &silo_.bin_.inplace_.buffer_[0] - &src.inplace_.buffer_[0];
      iov_base = ptr + offset;
      MDBX_CONSTEXPR_ASSERT(is_freestanding());
    }
  }
 
  silo silo_;
 
  void insulate() {
    assert(is_reference());
    iov_base = silo_.assign(iov_base, iov_len);
  }
 
  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR const byte *silo_begin() const noexcept {
    return static_cast<const byte *>(silo_.data());
  }
 
  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR const byte *silo_end() const noexcept {
    return silo_begin() + silo_.capacity();
  }
 
  struct data_preserver : public exception_thunk {
    buffer data;
    data_preserver(allocator_type &alloc) : data(alloc) {}
    static int callback(void *context, MDBX_val *target, const void *src, size_t bytes) noexcept {
      auto self = static_cast<data_preserver *>(context);
      assert(self->is_clean());
      assert(&self->data == target);
      (void)target;
      try {
        self->data.assign(src, bytes, false);
        return MDBX_RESULT_FALSE;
      } catch (... /* capture any exception to rethrow it over C code */) {
        self->capture();
        return MDBX_RESULT_TRUE;
      }
    }
    MDBX_CXX11_CONSTEXPR operator MDBX_preserve_func() const noexcept { return callback; }
    MDBX_CXX11_CONSTEXPR operator const buffer &() const noexcept { return data; }
    MDBX_CXX11_CONSTEXPR operator buffer &() noexcept { return data; }
  };
 
public:
 
  using move_assign_alloc = allocation_aware_details::move_assign_alloc<silo, allocator_type>;
  using copy_assign_alloc = allocation_aware_details::copy_assign_alloc<silo, allocator_type>;
  using swap_alloc = allocation_aware_details::swap_alloc<struct silo, allocator_type>;
 
  static constexpr bool is_swap_nothrow() noexcept { return swap_alloc::is_nothrow(); }

  MDBX_CXX20_CONSTEXPR allocator_type get_allocator() const { return silo_.get_allocator(); }

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR bool is_freestanding() const noexcept {
    static_assert(size_t(-intptr_t(max_length)) > max_length, "WTF?");
    return size_t(inherited::byte_ptr() - silo_begin()) < silo_.capacity();
  }

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR bool is_inplace() const noexcept {
    return silo_.is_inplace(inherited::data());
  }

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR bool is_reference() const noexcept { return !is_freestanding(); }

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR size_t capacity() const noexcept {
    return is_freestanding() ? silo_.capacity() : 0;
  }

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR size_t headroom() const noexcept {
    return is_freestanding() ? inherited::byte_ptr() - silo_begin() : 0;
  }

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR size_t tailroom() const noexcept {
    return is_freestanding() ? silo_end() - inherited::end_byte_ptr() : 0;
  }

  MDBX_CXX11_CONSTEXPR const byte *byte_ptr() const noexcept { return inherited::byte_ptr(); }

  MDBX_CXX11_CONSTEXPR const byte *end_byte_ptr() const noexcept { return inherited::end_byte_ptr(); }

  MDBX_CXX11_CONSTEXPR byte *byte_ptr() noexcept {
    MDBX_CONSTEXPR_ASSERT(is_freestanding());
    return inherited::byte_ptr();
  }

  MDBX_CXX11_CONSTEXPR byte *end_byte_ptr() noexcept {
    MDBX_CONSTEXPR_ASSERT(is_freestanding());
    return const_cast<byte *>(inherited::end_byte_ptr());
  }

  MDBX_CXX11_CONSTEXPR const char *char_ptr() const noexcept { return inherited::char_ptr(); }

  MDBX_CXX11_CONSTEXPR const char *end_char_ptr() const noexcept { return inherited::end_char_ptr(); }

  MDBX_CXX11_CONSTEXPR char *char_ptr() noexcept {
    MDBX_CONSTEXPR_ASSERT(is_freestanding());
    return const_cast<char *>(inherited::char_ptr());
  }

  MDBX_CXX11_CONSTEXPR char *end_char_ptr() noexcept {
    MDBX_CONSTEXPR_ASSERT(is_freestanding());
    return const_cast<char *>(inherited::end_char_ptr());
  }

  MDBX_CXX11_CONSTEXPR const void *data() const noexcept { return inherited::data(); }

  MDBX_CXX11_CONSTEXPR const void *end() const noexcept { return inherited::end(); }

  MDBX_CXX11_CONSTEXPR void *data() noexcept {
    MDBX_CONSTEXPR_ASSERT(is_freestanding());
    return const_cast<void *>(inherited::data());
  }

  MDBX_CXX11_CONSTEXPR void *end() noexcept {
    MDBX_CONSTEXPR_ASSERT(is_freestanding());
    return const_cast<void *>(inherited::end());
  }

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR size_t length() const noexcept {
    return MDBX_CONSTEXPR_ASSERT(is_reference() || inherited::end_byte_ptr() <= silo_end()), inherited::length();
  }

  MDBX_CXX14_CONSTEXPR buffer &set_length(size_t bytes) {
    MDBX_CONSTEXPR_ASSERT(is_reference() || inherited::byte_ptr() + bytes <= silo_end());
    inherited::set_length(bytes);
    return *this;
  }

  MDBX_CXX14_CONSTEXPR buffer &set_end(const void *ptr) {
    MDBX_CONSTEXPR_ASSERT(static_cast<const char *>(ptr) >= char_ptr());
    return set_length(static_cast<const char *>(ptr) - char_ptr());
  }

  void make_freestanding() {
    if (is_reference())
      insulate();
  }
 
  MDBX_CXX20_CONSTEXPR buffer() noexcept = default;
  MDBX_CXX20_CONSTEXPR buffer(const allocator_type &alloc) noexcept : silo_(alloc) {}
  MDBX_CXX20_CONSTEXPR buffer(const struct slice &src, bool make_reference,
                              const allocator_type &alloc = allocator_type());
 
  MDBX_CXX20_CONSTEXPR
  buffer(const void *ptr, size_t bytes, bool make_reference, const allocator_type &alloc = allocator_type())
      : buffer(inherited(ptr, bytes), make_reference, alloc) {}
 
  template <class CHAR, class T, class A> buffer(const ::std::basic_string<CHAR, T, A> &) = delete;
  template <class CHAR, class T, class A> buffer(const ::std::basic_string<CHAR, T, A> &&) = delete;
 
  buffer(const char *c_str, bool make_reference, const allocator_type &alloc = allocator_type())
      : buffer(inherited(c_str), make_reference, alloc) {}
 
#if defined(DOXYGEN) || (defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L)
  template <class CHAR, class T>
  MDBX_CXX20_CONSTEXPR buffer(const ::std::basic_string_view<CHAR, T> &view, bool make_reference,
                              const allocator_type &alloc = allocator_type())
      : buffer(inherited(view), make_reference, alloc) {}
#endif /* __cpp_lib_string_view >= 201606L */
 
  MDBX_CXX20_CONSTEXPR
  buffer(const struct slice &src, const allocator_type &alloc = allocator_type())
      : buffer(src, src.empty() || src.is_null(), alloc) {}
 
  MDBX_CXX20_CONSTEXPR
  buffer(const buffer &src)
      : buffer(src, allocator_traits::select_on_container_copy_construction(src.get_allocator())) {}
 
  MDBX_CXX20_CONSTEXPR
  buffer(const void *ptr, size_t bytes, const allocator_type &alloc = allocator_type())
      : buffer(inherited(ptr, bytes), alloc) {}
 
  template <class CHAR, class T, class A>
  MDBX_CXX20_CONSTEXPR buffer(const ::std::basic_string<CHAR, T, A> &str,
                              const allocator_type &alloc = allocator_type())
      : buffer(inherited(str), alloc) {}
 
  MDBX_CXX20_CONSTEXPR
  buffer(const char *c_str, const allocator_type &alloc = allocator_type()) : buffer(inherited(c_str), alloc) {}
 
#if defined(DOXYGEN) || (defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L)
  template <class CHAR, class T>
  MDBX_CXX20_CONSTEXPR buffer(const ::std::basic_string_view<CHAR, T> &view,
                              const allocator_type &alloc = allocator_type())
      : buffer(inherited(view), alloc) {}
#endif /* __cpp_lib_string_view >= 201606L */
 
  buffer(size_t head_room, size_t tail_room, const allocator_type &alloc = allocator_type())
      : silo_(check_length(head_room, tail_room), alloc) {
    iov_base = silo_.get();
    assert(iov_len == 0);
  }
 
  buffer(size_t capacity, const allocator_type &alloc = allocator_type()) : silo_(check_length(capacity), alloc) {
    iov_base = silo_.get();
    assert(iov_len == 0);
  }
 
  buffer(size_t head_room, const slice &src, size_t tail_room, const allocator_type &alloc = allocator_type())
      : silo_(check_length(head_room, src.length(), tail_room), alloc) {
    iov_base = memcpy(silo_.get(), src.data(), iov_len = src.length());
  }
 
  inline buffer(const txn &transaction, const slice &src, const allocator_type &alloc = allocator_type());
 
  buffer(buffer &&src) noexcept(move_assign_alloc::is_nothrow())
      : inherited(/* no move here */ src), silo_(::std::move(src.silo_), src.is_reference()) {
    /* CoverityScan issues an erroneous warning here about using an uninitialized object. Which is not true,
     * since in C++ (unlike Rust) an object remains initialized after a move-assignment operation; Moreover,
     * a destructor will be called for such an object (this is explicitly stated in all C++ standards, starting from the
     * 11th). */
    /* coverity[use_after_move] */
    fixup_import(src.silo_.bin_);
    src.invalidate();
  }

  MDBX_CXX14_CONSTEXPR static buffer null() noexcept { return buffer(inherited::null()); }

  MDBX_CXX14_CONSTEXPR static buffer invalid() noexcept { return buffer(inherited::invalid()); }
 
  template <typename POD>
  static buffer wrap(const POD &pod, bool make_reference = false, const allocator_type &alloc = allocator_type()) {
    return buffer(inherited::wrap(pod), make_reference, alloc);
  }

  static buffer hex(const slice &source, bool uppercase = false, unsigned wrap_width = 0,
                    const allocator_type &alloc = allocator_type()) {
    return source.template encode_hex<ALLOCATOR, CAPACITY_POLICY>(uppercase, wrap_width, alloc);
  }

  static buffer base58(const slice &source, unsigned wrap_width = 0, const allocator_type &alloc = allocator_type()) {
    return source.template encode_base58<ALLOCATOR, CAPACITY_POLICY>(wrap_width, alloc);
  }

  static buffer base64(const slice &source, unsigned wrap_width = 0, const allocator_type &alloc = allocator_type()) {
    return source.template encode_base64<ALLOCATOR, CAPACITY_POLICY>(wrap_width, alloc);
  }

  template <typename POD>
  static buffer hex(const POD &pod, bool uppercase = false, unsigned wrap_width = 0,
                    const allocator_type &alloc = allocator_type()) {
    return hex(inherited::wrap(pod), uppercase, wrap_width, alloc);
  }

  template <typename POD>
  static buffer base58(const POD &pod, unsigned wrap_width = 0, const allocator_type &alloc = allocator_type()) {
    return base58(inherited::wrap(pod), wrap_width, alloc);
  }

  template <typename POD>
  static buffer base64(const POD &pod, unsigned wrap_width = 0, const allocator_type &alloc = allocator_type()) {
    return base64(inherited::wrap(pod), wrap_width, alloc);
  }

  buffer encode_hex(bool uppercase = false, unsigned wrap_width = 0,
                    const allocator_type &alloc = allocator_type()) const {
    return inherited::template encode_hex<ALLOCATOR, CAPACITY_POLICY>(uppercase, wrap_width, alloc);
  }

  buffer encode_base58(unsigned wrap_width = 0, const allocator_type &alloc = allocator_type()) const {
    return inherited::template encode_base58<ALLOCATOR, CAPACITY_POLICY>(wrap_width, alloc);
  }

  buffer encode_base64(unsigned wrap_width = 0, const allocator_type &alloc = allocator_type()) const {
    return inherited::template encode_base64<ALLOCATOR, CAPACITY_POLICY>(wrap_width, alloc);
  }

  static buffer hex_decode(const slice &source, bool ignore_spaces = false,
                           const allocator_type &alloc = allocator_type()) {
    return source.template hex_decode<ALLOCATOR, CAPACITY_POLICY>(ignore_spaces, alloc);
  }

  static buffer base58_decode(const slice &source, bool ignore_spaces = false,
                              const allocator_type &alloc = allocator_type()) {
    return source.template base58_decode<ALLOCATOR, CAPACITY_POLICY>(ignore_spaces, alloc);
  }

  static buffer base64_decode(const slice &source, bool ignore_spaces = false,
                              const allocator_type &alloc = allocator_type()) {
    return source.template base64_decode<ALLOCATOR, CAPACITY_POLICY>(ignore_spaces, alloc);
  }

  buffer hex_decode(bool ignore_spaces = false, const allocator_type &alloc = allocator_type()) const {
    return hex_decode(*this, ignore_spaces, alloc);
  }

  buffer base58_decode(bool ignore_spaces = false, const allocator_type &alloc = allocator_type()) const {
    return base58_decode(*this, ignore_spaces, alloc);
  }

  buffer base64_decode(bool ignore_spaces = false, const allocator_type &alloc = allocator_type()) const {
    return base64_decode(*this, ignore_spaces, alloc);
  }

  void reserve(size_t wanna_headroom, size_t wanna_tailroom) {
    wanna_headroom = ::std::min(
        ::std::max(headroom(), wanna_headroom),
        (wanna_headroom < max_length - pettiness_threshold) ? wanna_headroom + pettiness_threshold : wanna_headroom);
    wanna_tailroom = ::std::min(
        ::std::max(tailroom(), wanna_tailroom),
        (wanna_tailroom < max_length - pettiness_threshold) ? wanna_tailroom + pettiness_threshold : wanna_tailroom);
    const size_t wanna_capacity = check_length(wanna_headroom, length(), wanna_tailroom);
    silo_.resize(wanna_capacity, wanna_headroom, *this);
    assert(headroom() >= wanna_headroom && headroom() <= wanna_headroom + pettiness_threshold);
    assert(tailroom() >= wanna_tailroom && tailroom() <= wanna_tailroom + pettiness_threshold);
  }

  void reserve_headroom(size_t wanna_headroom) { reserve(wanna_headroom, 0); }

  void reserve_tailroom(size_t wanna_tailroom) { reserve(0, wanna_tailroom); }
 
  buffer &assign_reference(const void *ptr, size_t bytes) {
    silo_.clear();
    inherited::assign(ptr, bytes);
    return *this;
  }
 
  buffer &assign_freestanding(const void *ptr, size_t bytes) {
    inherited::assign(silo_.assign(static_cast<const typename silo::value_type *>(ptr), check_length(bytes)), bytes);
    return *this;
  }
 
  MDBX_CXX20_CONSTEXPR void swap(buffer &other) noexcept(swap_alloc::is_nothrow()) {
    const auto pair = silo::exchange(silo_, is_reference(), other.silo_, other.is_reference());
    std::swap(iov_base, other.iov_base);
    std::swap(iov_len, other.iov_len);
    if (pair.first)
      fixup_import(other.silo_.bin_);
    if (pair.second)
      other.fixup_import(silo_.bin_);
  }
 
  MDBX_CXX20_CONSTEXPR friend void swap(buffer &left, buffer &right) noexcept(buffer::is_swap_nothrow()) {
    left.swap(right);
  }
 
  static buffer clone(const buffer &src, const allocator_type &alloc = allocator_type()) {
    return buffer(src.headroom(), src, src.tailroom(), alloc);
  }
 
  MDBX_CXX20_CONSTEXPR buffer make_inplace_or_reference() const {
    return buffer(slice(), !is_inplace(), allocator_traits::select_on_container_copy_construction(get_allocator()));
  }
 
  MDBX_CXX20_CONSTEXPR buffer &assign(size_t headroom, const buffer &src, size_t tailroom) {
    const size_t whole_capacity = check_length(headroom, src.length(), tailroom);
    invalidate();
    if MDBX_IF_CONSTEXPR (!allocation_aware_details::template allocator_is_always_equal<allocator_type>()) {
      if (MDBX_UNLIKELY(silo_.get_allocator() != src.silo_.get_allocator()))
        MDBX_CXX20_UNLIKELY {
          silo_.release();
          allocation_aware_details::copy_assign_alloc<silo, allocator_type>::propagate(&silo_, src.silo_);
        }
    }
 
    iov_base = silo_.template reshape<true>(whole_capacity, headroom, src.data(), src.length());
    iov_len = src.length();
    return *this;
  }
 
  MDBX_CXX20_CONSTEXPR buffer &assign(const buffer &src, bool make_reference = false) {
    invalidate();
    if MDBX_IF_CONSTEXPR (!allocation_aware_details::template allocator_is_always_equal<allocator_type>()) {
      if (MDBX_UNLIKELY(silo_.get_allocator() != src.silo_.get_allocator()))
        MDBX_CXX20_UNLIKELY {
          silo_.release();
          allocation_aware_details::copy_assign_alloc<silo, allocator_type>::propagate(&silo_, src.silo_);
        }
    }
 
    if (make_reference) {
      silo_.release();
      iov_base = src.iov_base;
    } else {
      iov_base = silo_.template reshape<true>(src.length(), 0, src.data(), src.length());
    }
    iov_len = src.length();
    return *this;
  }
 
  MDBX_CXX20_CONSTEXPR buffer &
  assign(buffer &&src) noexcept(allocation_aware_details::move_assign_alloc<silo, allocator_type>::is_nothrow()) {
    const bool is_reference = src.is_reference();
    inherited::assign(std::move(src));
    if (silo_.assign_move(std::move(src.silo_), is_reference))
      fixup_import(src.silo_.bin_);
    return *this;
  }
 
  buffer &assign(const void *ptr, size_t bytes, bool make_reference = false) {
    return make_reference ? assign_reference(ptr, bytes) : assign_freestanding(ptr, bytes);
  }
 
  buffer &assign(const struct slice &src, bool make_reference = false) {
    return assign(src.data(), src.length(), make_reference);
  }
 
  buffer &assign(const ::MDBX_val &src, bool make_reference = false) {
    return assign(src.iov_base, src.iov_len, make_reference);
  }
 
  buffer &assign(struct slice &&src, bool make_reference = false) {
    assign(src.data(), src.length(), make_reference);
    src.invalidate();
    return *this;
  }
 
  buffer &assign(::MDBX_val &&src, bool make_reference = false) {
    assign(src.iov_base, src.iov_len, make_reference);
    src.iov_base = nullptr;
    return *this;
  }
 
  buffer &assign(const void *begin, const void *end, bool make_reference = false) {
    return assign(begin, static_cast<const byte *>(end) - static_cast<const byte *>(begin), make_reference);
  }
 
  template <class CHAR, class T, class A>
  buffer &assign(const ::std::basic_string<CHAR, T, A> &str, bool make_reference = false) {
    return assign(str.data(), str.length(), make_reference);
  }
 
  buffer &assign(const char *c_str, bool make_reference = false) {
    return assign(c_str, strlen(c_str), make_reference);
  }
 
#if defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L
  template <class CHAR, class T>
  buffer &assign(const ::std::basic_string_view<CHAR, T> &view, bool make_reference = false) {
    return assign(view.data(), view.length(), make_reference);
  }
 
  template <class CHAR, class T> buffer &assign(::std::basic_string_view<CHAR, T> &&view, bool make_reference = false) {
    assign(view.data(), view.length(), make_reference);
    view = {};
    return *this;
  }
#endif /* __cpp_lib_string_view >= 201606L */
 
  buffer &operator=(const buffer &src) { return assign(src); }
 
  buffer &operator=(buffer &&src) noexcept(move_assign_alloc::is_nothrow()) { return assign(::std::move(src)); }
 
  buffer &operator=(const struct slice &src) { return assign(src); }
 
  buffer &operator=(struct slice &&src) { return assign(::std::move(src)); }
 
#if defined(DOXYGEN) || (defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L)
  template <class CHAR, class T> buffer &operator=(const ::std::basic_string_view<CHAR, T> &view) noexcept {
    return assign(view.begin(), view.length());
  }
#endif /* __cpp_lib_string_view >= 201606L */
 
  template <class CHAR, class T, class A>
  MDBX_CXX20_CONSTEXPR explicit operator ::std::basic_string<CHAR, T, A>() const {
    return as_string<CHAR, T, A>();
  }

  void clear() noexcept { inherited::assign(silo_.clear(), size_t(0)); }

  void clear_and_reserve(size_t whole_capacity, size_t headroom = 0) noexcept {
    inherited::assign(silo_.clear_and_reserve(whole_capacity, headroom), size_t(0));
  }

  void shrink_to_fit() { silo_.resize(length(), 0, *this); }
 
  buffer &append(const void *src, size_t bytes) {
    if (MDBX_UNLIKELY(tailroom() < check_length(bytes)))
      MDBX_CXX20_UNLIKELY reserve_tailroom(bytes);
    memcpy(end_byte_ptr(), src, bytes);
    iov_len += bytes;
    return *this;
  }
 
  buffer &append(const byte c) {
    if (MDBX_UNLIKELY(tailroom() < 1))
      MDBX_CXX20_UNLIKELY reserve_tailroom(1);
    *end_byte_ptr() = c;
    iov_len += 1;
    return *this;
  }
 
  buffer &append(const struct slice &chunk) { return append(chunk.data(), chunk.size()); }
 
  buffer &add_header(const void *src, size_t bytes) {
    if (MDBX_UNLIKELY(headroom() < check_length(bytes)))
      MDBX_CXX20_UNLIKELY reserve_headroom(bytes);
    iov_base = memcpy(byte_ptr() - bytes, src, bytes);
    iov_len += bytes;
    return *this;
  }
 
  buffer &add_header(const struct slice &chunk) { return add_header(chunk.data(), chunk.size()); }
 
  template <MDBX_CXX20_CONCEPT(MutableByteProducer, PRODUCER)> buffer &append_producer(PRODUCER &producer) {
    const size_t wanna_bytes = producer.envisage_result_length();
    if (MDBX_UNLIKELY(tailroom() < check_length(wanna_bytes)))
      MDBX_CXX20_UNLIKELY reserve_tailroom(wanna_bytes);
    return set_end(producer.write_bytes(end_char_ptr(), tailroom()));
  }
 
  template <MDBX_CXX20_CONCEPT(ImmutableByteProducer, PRODUCER)> buffer &append_producer(const PRODUCER &producer) {
    const size_t wanna_bytes = producer.envisage_result_length();
    if (MDBX_UNLIKELY(tailroom() < check_length(wanna_bytes)))
      MDBX_CXX20_UNLIKELY reserve_tailroom(wanna_bytes);
    return set_end(producer.write_bytes(end_char_ptr(), tailroom()));
  }
 
  buffer &append_hex(const struct slice &data, bool uppercase = false, unsigned wrap_width = 0) {
    return append_producer(to_hex(data, uppercase, wrap_width));
  }
 
  buffer &append_base58(const struct slice &data, unsigned wrap_width = 0) {
    return append_producer(to_base58(data, wrap_width));
  }
 
  buffer &append_base64(const struct slice &data, unsigned wrap_width = 0) {
    return append_producer(to_base64(data, wrap_width));
  }
 
  buffer &append_decoded_hex(const struct slice &data, bool ignore_spaces = false) {
    return append_producer(from_hex(data, ignore_spaces));
  }
 
  buffer &append_decoded_base58(const struct slice &data, bool ignore_spaces = false) {
    return append_producer(from_base58(data, ignore_spaces));
  }
 
  buffer &append_decoded_base64(const struct slice &data, bool ignore_spaces = false) {
    return append_producer(from_base64(data, ignore_spaces));
  }
 
  buffer &append_u8(uint_fast8_t u8) {
    if (MDBX_UNLIKELY(tailroom() < 1))
      MDBX_CXX20_UNLIKELY reserve_tailroom(1);
    *end_byte_ptr() = uint8_t(u8);
    iov_len += 1;
    return *this;
  }
 
  buffer &append_byte(uint_fast8_t byte) { return append_u8(byte); }
 
  buffer &append_u16(uint_fast16_t u16) {
    if (MDBX_UNLIKELY(tailroom() < 2))
      MDBX_CXX20_UNLIKELY reserve_tailroom(2);
    const auto ptr = end_byte_ptr();
    ptr[0] = uint8_t(u16);
    ptr[1] = uint8_t(u16 >> 8);
    iov_len += 2;
    return *this;
  }
 
  buffer &append_u24(uint_fast32_t u24) {
    if (MDBX_UNLIKELY(tailroom() < 3))
      MDBX_CXX20_UNLIKELY reserve_tailroom(3);
    const auto ptr = end_byte_ptr();
    ptr[0] = uint8_t(u24);
    ptr[1] = uint8_t(u24 >> 8);
    ptr[2] = uint8_t(u24 >> 16);
    iov_len += 3;
    return *this;
  }
 
  buffer &append_u32(uint_fast32_t u32) {
    if (MDBX_UNLIKELY(tailroom() < 4))
      MDBX_CXX20_UNLIKELY reserve_tailroom(4);
    const auto ptr = end_byte_ptr();
    ptr[0] = uint8_t(u32);
    ptr[1] = uint8_t(u32 >> 8);
    ptr[2] = uint8_t(u32 >> 16);
    ptr[3] = uint8_t(u32 >> 24);
    iov_len += 4;
    return *this;
  }
 
  buffer &append_u48(uint_fast64_t u48) {
    if (MDBX_UNLIKELY(tailroom() < 6))
      MDBX_CXX20_UNLIKELY reserve_tailroom(6);
    const auto ptr = end_byte_ptr();
    ptr[0] = uint8_t(u48);
    ptr[1] = uint8_t(u48 >> 8);
    ptr[2] = uint8_t(u48 >> 16);
    ptr[3] = uint8_t(u48 >> 24);
    ptr[4] = uint8_t(u48 >> 32);
    ptr[5] = uint8_t(u48 >> 40);
    iov_len += 6;
    return *this;
  }
 
  buffer &append_u64(uint_fast64_t u64) {
    if (MDBX_UNLIKELY(tailroom() < 8))
      MDBX_CXX20_UNLIKELY reserve_tailroom(8);
    const auto ptr = end_byte_ptr();
    ptr[0] = uint8_t(u64);
    ptr[1] = uint8_t(u64 >> 8);
    ptr[2] = uint8_t(u64 >> 16);
    ptr[3] = uint8_t(u64 >> 24);
    ptr[4] = uint8_t(u64 >> 32);
    ptr[5] = uint8_t(u64 >> 40);
    ptr[6] = uint8_t(u64 >> 48);
    ptr[7] = uint8_t(u64 >> 56);
    iov_len += 8;
    return *this;
  }
 
  //----------------------------------------------------------------------------
 
  template <size_t SIZE> static buffer key_from(const char (&text)[SIZE], bool make_reference = true) {
    return buffer(inherited(text), make_reference);
  }
 
#if defined(DOXYGEN) || (defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L)
  template <class CHAR, class T>
  static buffer key_from(const ::std::basic_string_view<CHAR, T> &src, bool make_reference = false) {
    return buffer(src, make_reference);
  }
#endif /* __cpp_lib_string_view >= 201606L */
 
  static buffer key_from(const char *src, bool make_reference = false) { return buffer(src, make_reference); }
 
  template <class CHAR, class T, class A>
  static buffer key_from(const ::std::basic_string<CHAR, T, A> &src, bool make_reference = false) {
    return buffer(src, make_reference);
  }
 
  static buffer key_from(buffer &&src) noexcept { return buffer(::std::move(src)); }
 
  static buffer key_from_double(const double ieee754_64bit) { return wrap(::mdbx_key_from_double(ieee754_64bit)); }
 
  static buffer key_from(const double ieee754_64bit) { return key_from_double(ieee754_64bit); }
 
  static buffer key_from(const double *ieee754_64bit) { return wrap(::mdbx_key_from_ptrdouble(ieee754_64bit)); }
 
  static buffer key_from_u64(const uint64_t unsigned_int64) { return wrap(unsigned_int64); }
 
  static buffer key_from(const uint64_t unsigned_int64) { return key_from_u64(unsigned_int64); }
 
  static buffer key_from_i64(const int64_t signed_int64) { return wrap(::mdbx_key_from_int64(signed_int64)); }
 
  static buffer key_from(const int64_t signed_int64) { return key_from_i64(signed_int64); }
 
  static buffer key_from_jsonInteger(const int64_t json_integer) {
    return wrap(::mdbx_key_from_jsonInteger(json_integer));
  }
 
  static buffer key_from_float(const float ieee754_32bit) { return wrap(::mdbx_key_from_float(ieee754_32bit)); }
 
  static buffer key_from(const float ieee754_32bit) { return key_from_float(ieee754_32bit); }
 
  static buffer key_from(const float *ieee754_32bit) { return wrap(::mdbx_key_from_ptrfloat(ieee754_32bit)); }
 
  static buffer key_from_u32(const uint32_t unsigned_int32) { return wrap(unsigned_int32); }
 
  static buffer key_from(const uint32_t unsigned_int32) { return key_from_u32(unsigned_int32); }
 
  static buffer key_from_i32(const int32_t signed_int32) { return wrap(::mdbx_key_from_int32(signed_int32)); }
 
  static buffer key_from(const int32_t signed_int32) { return key_from_i32(signed_int32); }
 
  const slice &slice() const noexcept { return *this; }
};
 
template <typename ALLOCATOR, typename CAPACITY_POLICY> struct buffer_pair_spec {
  using buffer_type = buffer<ALLOCATOR, CAPACITY_POLICY>;
  using allocator_type = typename buffer_type::allocator_type;
  using allocator_traits = typename buffer_type::allocator_traits;
  using reservation_policy = CAPACITY_POLICY;
  using stl_pair = ::std::pair<buffer_type, buffer_type>;
  buffer_type key, value;
 
  MDBX_CXX20_CONSTEXPR buffer_pair_spec() noexcept = default;
  MDBX_CXX20_CONSTEXPR
  buffer_pair_spec(const allocator_type &alloc) noexcept : key(alloc), value(alloc) {}
 
  buffer_pair_spec(const buffer_type &key, const buffer_type &value, const allocator_type &alloc = allocator_type())
      : key(key, alloc), value(value, alloc) {}
  buffer_pair_spec(const buffer_type &key, const buffer_type &value, bool make_reference,
                   const allocator_type &alloc = allocator_type())
      : key(key, make_reference, alloc), value(value, make_reference, alloc) {}
 
  buffer_pair_spec(const stl_pair &pair, const allocator_type &alloc = allocator_type())
      : buffer_pair_spec(pair.first, pair.second, alloc) {}
  buffer_pair_spec(const stl_pair &pair, bool make_reference, const allocator_type &alloc = allocator_type())
      : buffer_pair_spec(pair.first, pair.second, make_reference, alloc) {}
 
  buffer_pair_spec(const slice &key, const slice &value, const allocator_type &alloc = allocator_type())
      : key(key, alloc), value(value, alloc) {}
  buffer_pair_spec(const slice &key, const slice &value, bool make_reference,
                   const allocator_type &alloc = allocator_type())
      : key(key, make_reference, alloc), value(value, make_reference, alloc) {}
 
  buffer_pair_spec(const pair &pair, const allocator_type &alloc = allocator_type())
      : buffer_pair_spec(pair.key, pair.value, alloc) {}
  buffer_pair_spec(const pair &pair, bool make_reference, const allocator_type &alloc = allocator_type())
      : buffer_pair_spec(pair.key, pair.value, make_reference, alloc) {}
 
  buffer_pair_spec(const txn &transacton, const slice &key, const slice &value,
                   const allocator_type &alloc = allocator_type())
      : key(transacton, key, alloc), value(transacton, value, alloc) {}
  buffer_pair_spec(const txn &transaction, const pair &pair, const allocator_type &alloc = allocator_type())
      : buffer_pair_spec(transaction, pair.key, pair.value, alloc) {}
 
  buffer_pair_spec(buffer_type &&key, buffer_type &&value) noexcept(buffer_type::move_assign_alloc::is_nothrow())
      : key(::std::move(key)), value(::std::move(value)) {}
  buffer_pair_spec(const buffer_pair_spec &) = default;
  buffer_pair_spec(buffer_pair_spec &&pair) noexcept(buffer_type::move_assign_alloc::is_nothrow())
      : buffer_pair_spec(::std::move(pair.key), ::std::move(pair.value)) {}
 
  buffer_pair_spec &operator=(const buffer_pair_spec &) = default;
  buffer_pair_spec &operator=(buffer_pair_spec &&src) {
    key.assign(std::move(src.key));
    value.assign(std::move(src.value));
    return *this;
  }
 
  buffer_pair_spec &operator=(const pair &src) {
    key.assign(src.key);
    value.assign(src.value);
    return *this;
  }
  buffer_pair_spec &operator=(pair &&src) {
    key.assign(std::move(src.key));
    value.assign(std::move(src.value));
    return *this;
  }
  buffer_pair_spec &operator=(const stl_pair &src) {
    key.assign(src.first);
    value.assign(src.second);
    return *this;
  }
  buffer_pair_spec &operator=(stl_pair &&src) {
    key.assign(std::move(src.first));
    value.assign(std::move(src.second));
    return *this;
  }

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR bool is_freestanding() const noexcept {
    return key.is_freestanding() && value.is_freestanding();
  }

  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR bool is_reference() const noexcept {
    return key.is_reference() || value.is_reference();
  }

  void make_freestanding() {
    key.make_freestanding();
    value.make_freestanding();
  }
 
  operator pair() const noexcept { return pair(key, value); }
};


class cache_entry : public MDBX_cache_entry_t {
public:
  cache_entry() noexcept { reset(); }
  cache_entry(const cache_entry &) noexcept = default;
  cache_entry &operator=(const cache_entry &) noexcept = default;
  cache_entry(cache_entry &&other) noexcept {
    *this = other;
    other.reset();
  }
  void reset() noexcept { mdbx_cache_init(this); }
};
 
//------------------------------------------------------------------------------

enum loop_control { continue_loop = 0, exit_loop = INT32_MIN };

enum class key_mode {
  usual = MDBX_DB_DEFAULTS,  
  reverse = MDBX_REVERSEKEY, 
  ordinal = MDBX_INTEGERKEY, 
  msgpack = -1               
};
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_usual(key_mode mode) noexcept {
  return (MDBX_db_flags_t(mode) & (MDBX_REVERSEKEY | MDBX_INTEGERKEY)) == 0;
}
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_ordinal(key_mode mode) noexcept {
  return (MDBX_db_flags_t(mode) & MDBX_INTEGERKEY) != 0;
}
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_samelength(key_mode mode) noexcept {
  return (MDBX_db_flags_t(mode) & MDBX_INTEGERKEY) != 0;
}
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_reverse(key_mode mode) noexcept {
  return (MDBX_db_flags_t(mode) & MDBX_REVERSEKEY) != 0;
}
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_msgpack(key_mode mode) noexcept { return mode == key_mode::msgpack; }

enum class value_mode {
  single = MDBX_DB_DEFAULTS, 
  multi = MDBX_DUPSORT,      
#if CONSTEXPR_ENUM_FLAGS_OPERATIONS || defined(DOXYGEN)
  multi_reverse = MDBX_DUPSORT | MDBX_REVERSEDUP,  
  multi_samelength = MDBX_DUPSORT | MDBX_DUPFIXED, 
  multi_ordinal = MDBX_DUPSORT | MDBX_DUPFIXED | MDBX_INTEGERDUP, 
  multi_reverse_samelength =
      MDBX_DUPSORT | MDBX_REVERSEDUP | MDBX_DUPFIXED, 
#else
  multi_reverse = uint32_t(MDBX_DUPSORT) | uint32_t(MDBX_REVERSEDUP),
  multi_samelength = uint32_t(MDBX_DUPSORT) | uint32_t(MDBX_DUPFIXED),
  multi_ordinal = uint32_t(MDBX_DUPSORT) | uint32_t(MDBX_DUPFIXED) | uint32_t(MDBX_INTEGERDUP),
  multi_reverse_samelength = uint32_t(MDBX_DUPSORT) | uint32_t(MDBX_REVERSEDUP) | uint32_t(MDBX_DUPFIXED),
#endif
  msgpack = -1 
};
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_usual(value_mode mode) noexcept {
  return (MDBX_db_flags_t(mode) & (MDBX_DUPSORT | MDBX_INTEGERDUP | MDBX_DUPFIXED | MDBX_REVERSEDUP)) == 0;
}
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_multi(value_mode mode) noexcept {
  return (MDBX_db_flags_t(mode) & MDBX_DUPSORT) != 0;
}
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_ordinal(value_mode mode) noexcept {
  return (MDBX_db_flags_t(mode) & MDBX_INTEGERDUP) != 0;
}
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_samelength(value_mode mode) noexcept {
  return (MDBX_db_flags_t(mode) & MDBX_DUPFIXED) != 0;
}
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_reverse(value_mode mode) noexcept {
  return (MDBX_db_flags_t(mode) & MDBX_REVERSEDUP) != 0;
}
 
MDBX_CXX01_CONSTEXPR_ENUM bool is_msgpack(value_mode mode) noexcept { return mode == value_mode::msgpack; }

struct LIBMDBX_API_TYPE map_handle {
  MDBX_dbi dbi{0};
  MDBX_CXX11_CONSTEXPR map_handle() noexcept {}
  MDBX_CXX11_CONSTEXPR map_handle(MDBX_dbi dbi) noexcept : dbi(dbi) {}
  map_handle(const map_handle &) noexcept = default;
  map_handle &operator=(const map_handle &) noexcept = default;
  operator bool() const noexcept { return dbi != 0; }
  operator MDBX_dbi() const { return dbi; }
 
#if defined(__cpp_impl_three_way_comparison) && __cpp_impl_three_way_comparison >= 201907L
  friend MDBX_CXX11_CONSTEXPR auto operator<=>(const map_handle &a, const map_handle &b) noexcept {
    return a.dbi <=> b.dbi;
  }
#endif /* __cpp_impl_three_way_comparison */
  friend MDBX_CXX14_CONSTEXPR bool operator==(const map_handle &a, const map_handle &b) noexcept {
    return a.dbi == b.dbi;
  }
  friend MDBX_CXX14_CONSTEXPR bool operator<(const map_handle &a, const map_handle &b) noexcept {
    return a.dbi < b.dbi;
  }
  friend MDBX_CXX14_CONSTEXPR bool operator>(const map_handle &a, const map_handle &b) noexcept {
    return a.dbi > b.dbi;
  }
  friend MDBX_CXX14_CONSTEXPR bool operator<=(const map_handle &a, const map_handle &b) noexcept {
    return a.dbi <= b.dbi;
  }
  friend MDBX_CXX14_CONSTEXPR bool operator>=(const map_handle &a, const map_handle &b) noexcept {
    return a.dbi >= b.dbi;
  }
  friend MDBX_CXX14_CONSTEXPR bool operator!=(const map_handle &a, const map_handle &b) noexcept {
    return a.dbi != b.dbi;
  }
 
  using flags = ::MDBX_db_flags_t;
  using state = ::MDBX_dbi_state_t;
  struct LIBMDBX_API_TYPE info {
    map_handle::flags flags;
    map_handle::state state;
    MDBX_CXX11_CONSTEXPR info(map_handle::flags flags, map_handle::state state) noexcept;
    info(const info &) noexcept = default;
    info &operator=(const info &) noexcept = default;
    MDBX_CXX11_CONSTEXPR_ENUM mdbx::key_mode key_mode() const noexcept;
    MDBX_CXX11_CONSTEXPR_ENUM mdbx::value_mode value_mode() const noexcept;
  };
};
 
using comparator = ::MDBX_cmp_func *;
inline comparator default_comparator(key_mode mode) noexcept {
  return ::mdbx_get_keycmp(static_cast<MDBX_db_flags_t>(mode));
}
inline comparator default_comparator(value_mode mode) noexcept {
  return ::mdbx_get_keycmp(static_cast<MDBX_db_flags_t>(mode));
}

enum put_mode {
  insert_unique = MDBX_NOOVERWRITE, 
  upsert = MDBX_UPSERT,             
  update = MDBX_CURRENT,            
};

class LIBMDBX_API_TYPE env {
  friend class txn;
 
protected:
  MDBX_env *handle_{nullptr};
  MDBX_CXX11_CONSTEXPR env(MDBX_env *ptr) noexcept;
 
public:
  MDBX_CXX11_CONSTEXPR env() noexcept = default;
  env(const env &) noexcept = default;
  env &operator=(const env &) noexcept = default;
  inline env &operator=(env &&) noexcept;
  inline env(env &&) noexcept;
  inline ~env() noexcept;
 
  MDBX_CXX14_CONSTEXPR operator bool() const noexcept;
  MDBX_CXX14_CONSTEXPR operator const MDBX_env *() const;
  MDBX_CXX14_CONSTEXPR operator MDBX_env *();
  friend MDBX_CXX11_CONSTEXPR bool operator==(const env &a, const env &b) noexcept;
  friend MDBX_CXX11_CONSTEXPR bool operator!=(const env &a, const env &b) noexcept;
 
  //----------------------------------------------------------------------------

 
  struct LIBMDBX_API_TYPE geometry {
    enum : intptr_t {
      default_value = -1,         
      minimal_value = 0,          
      maximal_value = INTPTR_MAX, 
      kB = 1000,                  
      MB = kB * 1000,             
      GB = MB * 1000,             
#if INTPTR_MAX > 0x7fffFFFFl
      TB = GB * 1000,  
      PB = TB * 1000,  
      EB = PB * 1000,  
#endif                 /* 64-bit intptr_t */
      KiB = 1024,      
      MiB = KiB << 10, 
      GiB = MiB << 10, 
#if INTPTR_MAX > 0x7fffFFFFl
      TiB = GiB << 10, 
      PiB = TiB << 10, 
      EiB = PiB << 10, 
#endif                 /* 64-bit intptr_t */
    };

    struct size {
      intptr_t bytes;
      MDBX_CXX11_CONSTEXPR size(intptr_t bytes) noexcept : bytes(bytes) {}
      MDBX_CXX11_CONSTEXPR operator intptr_t() const noexcept { return bytes; }
    };

    intptr_t size_lower{default_value};

    intptr_t size_now{default_value};

    intptr_t size_upper{default_value};

    intptr_t growth_step{default_value};

    intptr_t shrink_threshold{default_value};

    intptr_t pagesize{default_value};
 
    inline geometry &make_fixed(intptr_t size) noexcept;
    inline geometry &make_dynamic(intptr_t lower = default_value, intptr_t upper = default_value) noexcept;
    MDBX_CXX11_CONSTEXPR geometry() noexcept {}
    MDBX_CXX11_CONSTEXPR
    geometry(const geometry &) noexcept = default;
    MDBX_CXX11_CONSTEXPR geometry(intptr_t size_lower, intptr_t size_now = default_value,
                                  intptr_t size_upper = default_value, intptr_t growth_step = default_value,
                                  intptr_t shrink_threshold = default_value, intptr_t pagesize = default_value) noexcept
        : size_lower(size_lower), size_now(size_now), size_upper(size_upper), growth_step(growth_step),
          shrink_threshold(shrink_threshold), pagesize(pagesize) {}
  };

  enum mode {
    readonly,        
    write_file_io,   // don't available on OpenBSD
    write_mapped_io, 
    nested_transactions = write_file_io
  };

  enum durability {
    robust_synchronous,         
    half_synchronous_weak_last, 
    lazy_weak_tail,             
    whole_fragile               
  };

  struct LIBMDBX_API_TYPE reclaiming_options {
    bool lifo{false};
    bool coalesce{false};
    MDBX_CXX11_CONSTEXPR reclaiming_options() noexcept {}
    MDBX_CXX11_CONSTEXPR
    reclaiming_options(const reclaiming_options &) noexcept = default;
    MDBX_CXX14_CONSTEXPR reclaiming_options &operator=(const reclaiming_options &) noexcept = default;
    reclaiming_options(MDBX_env_flags_t) noexcept;
  };

  struct LIBMDBX_API_TYPE operate_options {
    bool no_sticky_threads{false};
    bool nested_transactions{false};
    bool exclusive{false};
    bool disable_readahead{false};
    bool disable_clear_memory{false};
    bool enable_validation{false};
    MDBX_CXX11_CONSTEXPR operate_options() noexcept {}
    MDBX_CXX11_CONSTEXPR
    operate_options(const operate_options &) noexcept = default;
    MDBX_CXX14_CONSTEXPR operate_options &operator=(const operate_options &) noexcept = default;
    operate_options(MDBX_env_flags_t) noexcept;
  };

  struct LIBMDBX_API_TYPE operate_parameters {
    unsigned max_maps{0};
    unsigned max_readers{0};
    env::mode mode{write_mapped_io};
    env::durability durability{robust_synchronous};
    env::reclaiming_options reclaiming;
    env::operate_options options;
 
    MDBX_CXX11_CONSTEXPR operate_parameters() noexcept {}
    MDBX_CXX11_CONSTEXPR
    operate_parameters(const unsigned max_maps, const unsigned max_readers = 0,
                       const env::mode mode = env::mode::write_mapped_io,
                       env::durability durability = env::durability::robust_synchronous,
                       const env::reclaiming_options &reclaiming = env::reclaiming_options(),
                       const env::operate_options &options = env::operate_options()) noexcept
        : max_maps(max_maps), max_readers(max_readers), mode(mode), durability(durability), reclaiming(reclaiming),
          options(options) {}
    MDBX_CXX11_CONSTEXPR
    operate_parameters(const operate_parameters &) noexcept = default;
    MDBX_CXX14_CONSTEXPR operate_parameters &operator=(const operate_parameters &) noexcept = default;
    MDBX_env_flags_t make_flags(bool accede = true,           
                                bool use_subdirectory = false 
    ) const;
    static env::mode mode_from_flags(MDBX_env_flags_t) noexcept;
    static env::durability durability_from_flags(MDBX_env_flags_t) noexcept;
    inline static env::reclaiming_options reclaiming_from_flags(MDBX_env_flags_t flags) noexcept;
    inline static env::operate_options options_from_flags(MDBX_env_flags_t flags) noexcept;
  };

  inline env::operate_parameters get_operation_parameters() const;
  inline env::mode get_mode() const;
  inline env::durability get_durability() const;
  inline env::reclaiming_options get_reclaiming() const;
  inline env::operate_options get_options() const;

  bool is_pristine() const;

  bool is_empty() const;

  static size_t default_pagesize() noexcept { return ::mdbx_default_pagesize(); }
 
  struct limits {
    limits() = delete;
    static inline size_t pagesize_min() noexcept;
    static inline size_t pagesize_max() noexcept;
    static inline size_t dbsize_min(intptr_t pagesize);
    static inline size_t dbsize_max(intptr_t pagesize);
    static inline size_t key_min(MDBX_db_flags_t flags) noexcept;
    static inline size_t key_min(key_mode mode) noexcept;
    static inline size_t key_max(intptr_t pagesize, MDBX_db_flags_t flags);
    static inline size_t key_max(intptr_t pagesize, key_mode mode);
    static inline size_t key_max(const env &, MDBX_db_flags_t flags);
    static inline size_t key_max(const env &, key_mode mode);
    static inline size_t value_min(MDBX_db_flags_t flags) noexcept;
    static inline size_t value_min(value_mode) noexcept;

    static inline size_t value_max(intptr_t pagesize, MDBX_db_flags_t flags);
    static inline size_t value_max(intptr_t pagesize, value_mode);
    static inline size_t value_max(const env &, MDBX_db_flags_t flags);
    static inline size_t value_max(const env &, value_mode);

    static inline size_t pairsize4page_max(intptr_t pagesize, MDBX_db_flags_t flags);
    static inline size_t pairsize4page_max(intptr_t pagesize, value_mode);
    static inline size_t pairsize4page_max(const env &, MDBX_db_flags_t flags);
    static inline size_t pairsize4page_max(const env &, value_mode);

    static inline size_t valsize4page_max(intptr_t pagesize, MDBX_db_flags_t flags);
    static inline size_t valsize4page_max(intptr_t pagesize, value_mode);
    static inline size_t valsize4page_max(const env &, MDBX_db_flags_t flags);
    static inline size_t valsize4page_max(const env &, value_mode);

    static inline size_t transaction_size_max(intptr_t pagesize);

    static inline size_t max_map_handles(void);
  };

  size_t dbsize_min() const { return limits::dbsize_min(this->get_pagesize()); }
  size_t dbsize_max() const { return limits::dbsize_max(this->get_pagesize()); }
  size_t key_min(key_mode mode) const noexcept { return limits::key_min(mode); }
  size_t key_max(key_mode mode) const { return limits::key_max(*this, mode); }
  size_t value_min(value_mode mode) const noexcept { return limits::value_min(mode); }
  size_t value_max(value_mode mode) const { return limits::value_max(*this, mode); }
  size_t transaction_size_max() const { return limits::transaction_size_max(this->get_pagesize()); }

#ifdef MDBX_STD_FILESYSTEM_PATH
  env &copy(const MDBX_STD_FILESYSTEM_PATH &destination, bool compactify, bool force_dynamic_size = false);
#endif /* MDBX_STD_FILESYSTEM_PATH */
#if defined(_WIN32) || defined(_WIN64) || defined(DOXYGEN)
  env &copy(const ::std::wstring &destination, bool compactify, bool force_dynamic_size = false);
  env &copy(const wchar_t *destination, bool compactify, bool force_dynamic_size = false);
#endif /* Windows */
  env &copy(const ::std::string &destination, bool compactify, bool force_dynamic_size = false);
  env &copy(const char *destination, bool compactify, bool force_dynamic_size = false);

  env &copy(filehandle fd, bool compactify, bool force_dynamic_size = false);

  enum remove_mode {
    just_remove = MDBX_ENV_JUST_DELETE,
    ensure_unused = MDBX_ENV_ENSURE_UNUSED,
    wait_for_unused = MDBX_ENV_WAIT_FOR_UNUSED
  };

#ifdef MDBX_STD_FILESYSTEM_PATH
  static bool remove(const MDBX_STD_FILESYSTEM_PATH &pathname, const remove_mode mode = just_remove);
#endif /* MDBX_STD_FILESYSTEM_PATH */
#if defined(_WIN32) || defined(_WIN64) || defined(DOXYGEN)
  static bool remove(const ::std::wstring &pathname, const remove_mode mode = just_remove);
  static bool remove(const wchar_t *pathname, const remove_mode mode = just_remove);
#endif /* Windows */
  static bool remove(const ::std::string &pathname, const remove_mode mode = just_remove);
  static bool remove(const char *pathname, const remove_mode mode = just_remove);

  using stat = ::MDBX_stat;

  using info = ::MDBX_envinfo;

  inline stat get_stat() const;

  size_t get_pagesize() const { return get_stat().ms_psize; }

  inline info get_info() const;

  inline stat get_stat(const txn &) const;

  inline info get_info(const txn &) const;

  inline filehandle get_filehandle() const;

  path get_path() const;

  inline MDBX_env_flags_t get_flags() const;
 
  inline bool is_readonly() const { return (get_flags() & MDBX_RDONLY) != 0; }
 
  inline bool is_exclusive() const { return (get_flags() & MDBX_EXCLUSIVE) != 0; }
 
  inline bool is_cooperative() const { return !is_exclusive(); }
 
  inline bool is_writemap() const { return (get_flags() & MDBX_WRITEMAP) != 0; }
 
  inline bool is_readwite() const { return !is_readonly(); }
 
  inline bool is_nested_transactions_available() const { return (get_flags() & (MDBX_WRITEMAP | MDBX_RDONLY)) == 0; }

  inline unsigned max_readers() const;

  inline unsigned max_maps() const;

  inline void *get_context() const noexcept;

  inline env &set_context(void *your_context);

  inline env &set_sync_threshold(size_t bytes);

  inline size_t sync_threshold() const;
 
#if __cplusplus >= 201103L || defined(DOXYGEN)
  inline env &set_sync_period(const duration &period);

  inline duration sync_period() const;
#endif

  inline env &set_sync_period__seconds_16dot16(unsigned seconds_16dot16);

  inline unsigned sync_period__seconds_16dot16() const;

  inline env &set_sync_period__seconds_double(double seconds);

  inline double sync_period__seconds_double() const;

  enum class extra_runtime_option {
    max_maps = MDBX_opt_max_db,
    max_readers = MDBX_opt_max_readers,
    sync_bytes = MDBX_opt_sync_bytes,
    sync_period = MDBX_opt_sync_period,
    rp_augment_limit = MDBX_opt_rp_augment_limit,
    loose_limit = MDBX_opt_loose_limit,
    dp_reserve_limit = MDBX_opt_dp_reserve_limit,
    dp_limit = MDBX_opt_txn_dp_limit,
    dp_initial = MDBX_opt_txn_dp_initial,
    spill_max_denominator = MDBX_opt_spill_max_denominator,
    spill_min_denominator = MDBX_opt_spill_min_denominator,
    spill_parent4child_denominator = MDBX_opt_spill_parent4child_denominator,
    merge_threshold_16dot16_percent = MDBX_opt_merge_threshold_16dot16_percent,
    writethrough_threshold = MDBX_opt_writethrough_threshold,
    prefault_write_enable = MDBX_opt_prefault_write_enable,
  };

  inline env &set_extra_option(extra_runtime_option option, uint64_t value);

  inline uint64_t extra_option(extra_runtime_option option) const;

  inline env &alter_flags(MDBX_env_flags_t flags, bool on_off);

  inline env &set_geometry(const geometry &size);

  inline bool sync_to_disk(bool force = true, bool nonblock = false);

  bool poll_sync_to_disk() { return sync_to_disk(false, true); }

  inline void close_map(const map_handle &);

  struct reader_info {
    int slot;                 
    mdbx_pid_t pid;           
    mdbx_tid_t thread;        
    uint64_t transaction_id;  
    uint64_t transaction_lag; 
    size_t bytes_used;        
    size_t bytes_retained;    
 
    MDBX_CXX11_CONSTEXPR reader_info(int slot, mdbx_pid_t pid, mdbx_tid_t thread, uint64_t txnid, uint64_t lag,
                                     size_t used, size_t retained) noexcept;
  };

  template <typename VISITOR> inline int enumerate_readers(VISITOR &visitor);

  inline unsigned check_readers();

  inline env &set_HandleSlowReaders(MDBX_hsr_func *);

  inline MDBX_hsr_func *get_HandleSlowReaders() const noexcept;

  inline txn_managed start_read() const;

  inline txn_managed prepare_read() const;

  inline txn_managed start_write(txn &parent);

  inline txn_managed start_write(bool dont_wait = false);

  inline txn_managed try_start_write();
};

class LIBMDBX_API_TYPE env_managed : public env {
  using inherited = env;
  MDBX_CXX11_CONSTEXPR env_managed(MDBX_env *ptr) noexcept : inherited(ptr) {}
  void setup(unsigned max_maps, unsigned max_readers = 0);
 
public:
  MDBX_CXX11_CONSTEXPR env_managed() noexcept = default;

#ifdef MDBX_STD_FILESYSTEM_PATH
  env_managed(const MDBX_STD_FILESYSTEM_PATH &pathname, const operate_parameters &, bool accede = true);
#endif /* MDBX_STD_FILESYSTEM_PATH */
#if defined(_WIN32) || defined(_WIN64) || defined(DOXYGEN)
  env_managed(const ::std::wstring &pathname, const operate_parameters &, bool accede = true);
  explicit env_managed(const wchar_t *pathname, const operate_parameters &, bool accede = true);
#endif /* Windows */
  env_managed(const ::std::string &pathname, const operate_parameters &, bool accede = true);
  explicit env_managed(const char *pathname, const operate_parameters &, bool accede = true);

  struct create_parameters {
    env::geometry geometry;
    mdbx_mode_t file_mode_bits{0640};
    bool use_subdirectory{false};
    MDBX_CXX11_CONSTEXPR create_parameters() noexcept = default;
    create_parameters(const create_parameters &) noexcept = default;
  };

#ifdef MDBX_STD_FILESYSTEM_PATH
  env_managed(const MDBX_STD_FILESYSTEM_PATH &pathname, const create_parameters &, const operate_parameters &,
              bool accede = true);
#endif /* MDBX_STD_FILESYSTEM_PATH */
#if defined(_WIN32) || defined(_WIN64) || defined(DOXYGEN)
  env_managed(const ::std::wstring &pathname, const create_parameters &, const operate_parameters &,
              bool accede = true);
  explicit env_managed(const wchar_t *pathname, const create_parameters &, const operate_parameters &,
                       bool accede = true);
#endif /* Windows */
  env_managed(const ::std::string &pathname, const create_parameters &, const operate_parameters &, bool accede = true);
  explicit env_managed(const char *pathname, const create_parameters &, const operate_parameters &, bool accede = true);

  void close(bool dont_sync = false);
 
  env_managed(env_managed &&) = default;
  env_managed &operator=(env_managed &&other) noexcept {
    if (MDBX_UNLIKELY(handle_))
      MDBX_CXX20_UNLIKELY {
        assert(handle_ != other.handle_);
        close();
      }
    inherited::operator=(std::move(other));
    return *this;
  }
  env_managed(const env_managed &) = delete;
  env_managed &operator=(const env_managed &) = delete;
  virtual ~env_managed() noexcept;
};

class LIBMDBX_API_TYPE txn {
protected:
  friend class cursor;
  MDBX_txn *handle_{nullptr};
  MDBX_CXX11_CONSTEXPR txn(MDBX_txn *ptr) noexcept;
 
public:
  MDBX_CXX11_CONSTEXPR txn() noexcept = default;
  txn(const txn &) noexcept = default;
  txn &operator=(const txn &) noexcept = default;
  inline txn &operator=(txn &&) noexcept;
  inline txn(txn &&) noexcept;
  inline ~txn() noexcept;
 
  MDBX_CXX14_CONSTEXPR operator bool() const noexcept;
  MDBX_CXX14_CONSTEXPR operator const MDBX_txn *() const;
  MDBX_CXX14_CONSTEXPR operator MDBX_txn *();
  friend MDBX_CXX11_CONSTEXPR bool operator==(const txn &a, const txn &b) noexcept;
  friend MDBX_CXX11_CONSTEXPR bool operator!=(const txn &a, const txn &b) noexcept;

  inline ::mdbx::env env() const noexcept;
  inline MDBX_txn_flags_t flags() const;
  inline uint64_t id() const;

  inline void *get_context() const noexcept;

  inline txn &set_context(void *your_context);

  inline bool is_dirty(const void *ptr) const;

  inline bool is_dirty(const slice &item) const { return item && is_dirty(item.data()); }

  bool is_readonly() const { return (flags() & MDBX_TXN_RDONLY) != 0; }

  bool is_readwrite() const { return (flags() & MDBX_TXN_RDONLY) == 0; }
 
  using info = ::MDBX_txn_info;
  inline info get_info(bool scan_reader_lock_table = false) const;

  size_t size_max() const { return env().transaction_size_max(); }

  size_t size_current() const {
    assert(is_readwrite());
    return size_t(get_info().txn_space_dirty);
  }
 
  //----------------------------------------------------------------------------

  inline void reset_reading();

  inline void renew_reading();

  inline txn_managed clone(void *context = nullptr) const;

  inline void clone(txn_managed &txn_for_renew_into_clone, void *context = nullptr) const;

  inline void make_broken();

  inline void park_reading(bool autounpark = true);

  inline bool unpark_reading(bool restart_if_ousted = true);

  txn_managed start_nested();

  txn_managed start_nested(bool readonly);

  inline cursor_managed open_cursor(map_handle map) const;

  inline size_t release_all_cursors(bool unbind) const;

  inline size_t close_all_cursors() const { return release_all_cursors(false); }

  inline size_t unbind_all_cursors() const { return release_all_cursors(true); }

  inline map_handle open_map(const char *name, const ::mdbx::key_mode key_mode = ::mdbx::key_mode::usual,
                             const ::mdbx::value_mode value_mode = ::mdbx::value_mode::single) const;
  inline map_handle open_map(const ::std::string &name, const ::mdbx::key_mode key_mode = ::mdbx::key_mode::usual,
                             const ::mdbx::value_mode value_mode = ::mdbx::value_mode::single) const;
  inline map_handle open_map(const slice &name, const ::mdbx::key_mode key_mode = ::mdbx::key_mode::usual,
                             const ::mdbx::value_mode value_mode = ::mdbx::value_mode::single) const;

  inline map_handle open_map_accede(const char *name) const;
  inline map_handle open_map_accede(const ::std::string &name) const;
  inline map_handle open_map_accede(const slice &name) const;

  inline map_handle create_map(const char *name, const ::mdbx::key_mode key_mode = ::mdbx::key_mode::usual,
                               const ::mdbx::value_mode value_mode = ::mdbx::value_mode::single);
  inline map_handle create_map(const ::std::string &name, const ::mdbx::key_mode key_mode = ::mdbx::key_mode::usual,
                               const ::mdbx::value_mode value_mode = ::mdbx::value_mode::single);
  inline map_handle create_map(const slice &name, const ::mdbx::key_mode key_mode = ::mdbx::key_mode::usual,
                               const ::mdbx::value_mode value_mode = ::mdbx::value_mode::single);

  inline void drop_map(map_handle map);
  bool drop_map(const char *name, bool throw_if_absent = false);
  inline bool drop_map(const ::std::string &name, bool throw_if_absent = false);
  bool drop_map(const slice &name, bool throw_if_absent = false);

  inline void clear_map(map_handle map);
  bool clear_map(const char *name, bool throw_if_absent = false);
  inline bool clear_map(const ::std::string &name, bool throw_if_absent = false);
  bool clear_map(const slice &name, bool throw_if_absent = false);

  inline void rename_map(map_handle map, const char *new_name);
  inline void rename_map(map_handle map, const ::std::string &new_name);
  inline void rename_map(map_handle map, const slice &new_name);
  bool rename_map(const char *old_name, const char *new_name, bool throw_if_absent = false);
  bool rename_map(const ::std::string &old_name, const ::std::string &new_name, bool throw_if_absent = false);
  bool rename_map(const slice &old_name, const slice &new_name, bool throw_if_absent = false);
 
#if defined(DOXYGEN) || (defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L)

  inline map_handle open_map(const ::std::string_view &name, const ::mdbx::key_mode key_mode = ::mdbx::key_mode::usual,
                             const ::mdbx::value_mode value_mode = ::mdbx::value_mode::single) const {
    return open_map(slice(name), key_mode, value_mode);
  }

  inline map_handle open_map_accede(const ::std::string_view &name) const;
  inline map_handle create_map(const ::std::string_view &name,
                               const ::mdbx::key_mode key_mode = ::mdbx::key_mode::usual,
                               const ::mdbx::value_mode value_mode = ::mdbx::value_mode::single) {
    return create_map(slice(name), key_mode, value_mode);
  }

  bool drop_map(const ::std::string_view &name, bool throw_if_absent = false) {
    return drop_map(slice(name), throw_if_absent);
  }

  bool clear_map(const ::std::string_view &name, bool throw_if_absent = false) {
    return clear_map(slice(name), throw_if_absent);
  }

  inline void rename_map(map_handle map, const ::std::string_view &new_name);
  bool rename_map(const ::std::string_view &old_name, const ::std::string_view &new_name,
                  bool throw_if_absent = false) {
    return rename_map(slice(old_name), slice(new_name), throw_if_absent);
  }
#endif /* __cpp_lib_string_view >= 201606L */
 
  using map_stat = ::MDBX_stat;
  inline map_stat get_map_stat(map_handle map) const;
  inline uint32_t get_tree_deepmask(map_handle map) const;
  inline map_handle::info get_map_flags(map_handle map) const;
 
  using canary = ::MDBX_canary;
  inline txn &put_canary(const canary &);
  inline canary get_canary() const;

  inline uint64_t sequence(map_handle map) const;
  inline uint64_t sequence(map_handle map, uint64_t increment);

  inline int compare_keys(map_handle map, const slice &a, const slice &b) const noexcept;
  inline int compare_values(map_handle map, const slice &a, const slice &b) const noexcept;
  inline int compare_keys(map_handle map, const pair &a, const pair &b) const noexcept;
  inline int compare_values(map_handle map, const pair &a, const pair &b) const noexcept;

  inline slice get(map_handle map, const slice &key) const;
  inline slice get(map_handle map, slice key, size_t &values_count) const;
  inline slice get(map_handle map, const slice &key, const slice &value_at_absence) const;
  inline slice get(map_handle map, slice key, size_t &values_count, const slice &value_at_absence) const;
  inline pair_result get_equal_or_great(map_handle map, const slice &key) const;
  inline pair_result get_equal_or_great(map_handle map, const slice &key, const slice &value_at_absence) const;
 
  inline MDBX_error_t put(map_handle map, const slice &key, slice *value, MDBX_put_flags_t flags) noexcept;
  inline void put(map_handle map, const slice &key, slice value, put_mode mode);
  inline void insert(map_handle map, const slice &key, slice value);
  inline value_result try_insert(map_handle map, const slice &key, slice value);
  inline slice insert_reserve(map_handle map, const slice &key, size_t value_length);
  inline value_result try_insert_reserve(map_handle map, const slice &key, size_t value_length);
 
  inline void upsert(map_handle map, const slice &key, const slice &value);
  inline slice upsert_reserve(map_handle map, const slice &key, size_t value_length);
 
  inline void update(map_handle map, const slice &key, const slice &value);
  inline bool try_update(map_handle map, const slice &key, const slice &value);
  inline slice update_reserve(map_handle map, const slice &key, size_t value_length);
  inline value_result try_update_reserve(map_handle map, const slice &key, size_t value_length);
 
  void put(map_handle map, const pair &kv, put_mode mode) { return put(map, kv.key, kv.value, mode); }
  void insert(map_handle map, const pair &kv) { return insert(map, kv.key, kv.value); }
  value_result try_insert(map_handle map, const pair &kv) { return try_insert(map, kv.key, kv.value); }
  void upsert(map_handle map, const pair &kv) { return upsert(map, kv.key, kv.value); }

  inline bool erase(map_handle map, const slice &key);

  inline bool erase(map_handle map, const slice &key, const slice &value);

  inline void replace(map_handle map, const slice &key, slice old_value, const slice &new_value);

  template <class ALLOCATOR, typename CAPACITY_POLICY>
  inline buffer<ALLOCATOR, CAPACITY_POLICY>
  extract(map_handle map, const slice &key,
          const typename buffer<ALLOCATOR, CAPACITY_POLICY>::allocator_type &alloc =
              buffer<ALLOCATOR, CAPACITY_POLICY>::allocator_type());

  template <class ALLOCATOR, typename CAPACITY_POLICY>
  inline buffer<ALLOCATOR, CAPACITY_POLICY>
  replace(map_handle map, const slice &key, const slice &new_value,
          const typename buffer<ALLOCATOR, CAPACITY_POLICY>::allocator_type &alloc =
              buffer<ALLOCATOR, CAPACITY_POLICY>::allocator_type());
 
  template <class ALLOCATOR, typename CAPACITY_POLICY>
  inline buffer<ALLOCATOR, CAPACITY_POLICY>
  replace_reserve(map_handle map, const slice &key, slice &new_value,
                  const typename buffer<ALLOCATOR, CAPACITY_POLICY>::allocator_type &alloc =
                      buffer<ALLOCATOR, CAPACITY_POLICY>::allocator_type());

  inline void append(map_handle map, const slice &key, const slice &value, bool multivalue_order_preserved = true);
  inline void append(map_handle map, const pair &kv, bool multivalue_order_preserved = true) {
    return append(map, kv.key, kv.value, multivalue_order_preserved);
  }
 
  inline size_t put_multiple_samelength(map_handle map, const slice &key, const size_t value_length,
                                        const void *values_array, size_t values_count, put_mode mode,
                                        bool allow_partial = false);
  template <typename VALUE>
  size_t put_multiple_samelength(map_handle map, const slice &key, const VALUE *values_array, size_t values_count,
                                 put_mode mode, bool allow_partial = false) {
    static_assert(::std::is_standard_layout<VALUE>::value && !::std::is_pointer<VALUE>::value &&
                      !::std::is_array<VALUE>::value,
                  "Must be a standard layout type!");
    return put_multiple_samelength(map, key, sizeof(VALUE), values_array, values_count, mode, allow_partial);
  }
  template <typename VALUE>
  void put_multiple_samelength(map_handle map, const slice &key, const ::std::vector<VALUE> &vector, put_mode mode) {
    put_multiple_samelength(map, key, vector.data(), vector.size(), mode);
  }
 
  inline ptrdiff_t estimate(map_handle map, const pair &from, const pair &to) const;
  inline ptrdiff_t estimate(map_handle map, const slice &from, const slice &to) const;
  inline ptrdiff_t estimate_from_first(map_handle map, const slice &to) const;
  inline ptrdiff_t estimate_to_last(map_handle map, const slice &from) const;
};

class LIBMDBX_API_TYPE txn_managed : public txn {
  using inherited = txn;
  friend class env;
  friend class txn;
  MDBX_CXX11_CONSTEXPR txn_managed(MDBX_txn *ptr) noexcept : inherited(ptr) {}
 
public:
  MDBX_CXX11_CONSTEXPR txn_managed() noexcept = default;
  txn_managed(txn_managed &&) = default;
  txn_managed &operator=(txn_managed &&other) noexcept {
    if (MDBX_UNLIKELY(handle_))
      MDBX_CXX20_UNLIKELY {
        assert(handle_ != other.handle_);
        abort();
      }
    inherited::operator=(std::move(other));
    return *this;
  }
  txn_managed(const txn_managed &) = delete;
  txn_managed &operator=(const txn_managed &) = delete;
  ~txn_managed() noexcept;
 
  //----------------------------------------------------------------------------
  using finalization_latency = MDBX_commit_latency;

  void abort();
  void abort(finalization_latency *);
  void abort(finalization_latency &latency) { return abort(&latency); }
  finalization_latency abort_get_latency() {
    finalization_latency result;
    abort(&result);
    return result;
  }

  void commit();
  void commit(finalization_latency *);
  void commit(finalization_latency &latency) { return commit(&latency); }
  finalization_latency commit_get_latency() {
    finalization_latency result;
    commit(&result);
    return result;
  }

  bool checkpoint();
  bool checkpoint(finalization_latency *latency);
  bool checkpoint(finalization_latency &latency) { return checkpoint(&latency); }
  std::pair<bool, finalization_latency> checkpoint_get_latency() {
    finalization_latency latency;
    bool result = checkpoint(&latency);
    return std::make_pair(result, latency);
  }

  void commit_embark_read();
  void commit_embark_read(finalization_latency *latency);
  void commit_embark_read(finalization_latency &latency) { return commit_embark_read(&latency); }
  finalization_latency commit_embark_read_get_latency() {
    finalization_latency result;
    commit_embark_read(&result);
    return result;
  }

  bool amend(bool dont_wait = false);
};

class LIBMDBX_API_TYPE cursor {
protected:
  MDBX_cursor *handle_{nullptr};
 
public:
  MDBX_CXX11_CONSTEXPR cursor(MDBX_cursor *ptr) noexcept;
  MDBX_CXX11_CONSTEXPR cursor() noexcept = default;
  cursor(const cursor &) noexcept = default;
  cursor &operator=(const cursor &) noexcept = default;
  inline cursor &operator=(cursor &&) noexcept;
  inline cursor(cursor &&) noexcept;
  inline ~cursor() noexcept;
  inline cursor_managed clone(void *your_context = nullptr) const;
  MDBX_CXX14_CONSTEXPR operator bool() const noexcept;
  MDBX_CXX14_CONSTEXPR operator const MDBX_cursor *() const;
  MDBX_CXX14_CONSTEXPR operator MDBX_cursor *();
  friend MDBX_CXX11_CONSTEXPR bool operator==(const cursor &a, const cursor &b) noexcept;
  friend MDBX_CXX11_CONSTEXPR bool operator!=(const cursor &a, const cursor &b) noexcept;
 
  friend inline int compare_position_nothrow(const cursor &left, const cursor &right, bool ignore_nested) noexcept;
  friend inline int compare_position(const cursor &left, const cursor &right, bool ignore_nested);
 
  bool is_before_than(const cursor &other, bool ignore_nested = false) const {
    return compare_position(*this, other, ignore_nested) < 0;
  }
 
  bool is_same_or_before_than(const cursor &other, bool ignore_nested = false) const {
    return compare_position(*this, other, ignore_nested) <= 0;
  }
 
  bool is_same_position(const cursor &other, bool ignore_nested = false) const {
    return compare_position(*this, other, ignore_nested) == 0;
  }
 
  bool is_after_than(const cursor &other, bool ignore_nested = false) const {
    return compare_position(*this, other, ignore_nested) > 0;
  }
 
  bool is_same_or_after_than(const cursor &other, bool ignore_nested = false) const {
    return compare_position(*this, other, ignore_nested) >= 0;
  }

  inline void *get_context() const noexcept;

  inline cursor &set_context(void *your_context);
 
  enum move_operation {
    first = MDBX_FIRST,
    last = MDBX_LAST,
    next = MDBX_NEXT,
    previous = MDBX_PREV,
    get_current = MDBX_GET_CURRENT,
 
    multi_prevkey_lastvalue = MDBX_PREV_NODUP,
    multi_currentkey_firstvalue = MDBX_FIRST_DUP,
    multi_currentkey_prevvalue = MDBX_PREV_DUP,
    multi_currentkey_nextvalue = MDBX_NEXT_DUP,
    multi_currentkey_lastvalue = MDBX_LAST_DUP,
    multi_nextkey_firstvalue = MDBX_NEXT_NODUP,
 
    multi_find_pair = MDBX_GET_BOTH,
    multi_exactkey_lowerboundvalue = MDBX_GET_BOTH_RANGE,
 
    seek_key = MDBX_SET,
    key_exact = MDBX_SET_KEY,
    key_lowerbound = MDBX_SET_RANGE,
 
    /* Doubtless cursor positioning at a specified key. */
    key_lesser_than = MDBX_TO_KEY_LESSER_THAN,
    key_lesser_or_equal = MDBX_TO_KEY_LESSER_OR_EQUAL,
    key_equal = MDBX_TO_KEY_EQUAL,
    key_greater_or_equal = MDBX_TO_KEY_GREATER_OR_EQUAL,
    key_greater_than = MDBX_TO_KEY_GREATER_THAN,
 
    /* Doubtless cursor positioning at a specified key-value pair
     * for dupsort/multi-value hives. */
    multi_exactkey_value_lesser_than = MDBX_TO_EXACT_KEY_VALUE_LESSER_THAN,
    multi_exactkey_value_lesser_or_equal = MDBX_TO_EXACT_KEY_VALUE_LESSER_OR_EQUAL,
    multi_exactkey_value_equal = MDBX_TO_EXACT_KEY_VALUE_EQUAL,
    multi_exactkey_value_greater_or_equal = MDBX_TO_EXACT_KEY_VALUE_GREATER_OR_EQUAL,
    multi_exactkey_value_greater = MDBX_TO_EXACT_KEY_VALUE_GREATER_THAN,
 
    pair_lesser_than = MDBX_TO_PAIR_LESSER_THAN,
    pair_lesser_or_equal = MDBX_TO_PAIR_LESSER_OR_EQUAL,
    pair_equal = MDBX_TO_PAIR_EQUAL,
    pair_exact = pair_equal,
    pair_greater_or_equal = MDBX_TO_PAIR_GREATER_OR_EQUAL,
    pair_greater_than = MDBX_TO_PAIR_GREATER_THAN,
 
    batch_samelength = MDBX_GET_MULTIPLE,
    batch_samelength_next = MDBX_NEXT_MULTIPLE,
    batch_samelength_previous = MDBX_PREV_MULTIPLE,
    seek_and_batch_samelength = MDBX_SEEK_AND_GET_MULTIPLE
  };
 
  // TODO: добавить легковесный proxy-класс для замещения параметра throw_notfound более сложным набором опций,
  //       в том числе с explicit-конструктором из bool, чтобы защититься от неявной конвертации ключей поиска
  //       и других параметров в bool-throw_notfound.
 
  struct move_result : public pair_result {
    inline move_result(const cursor &cursor, bool throw_notfound);
    move_result(cursor &cursor, move_operation operation, bool throw_notfound)
        : move_result(cursor, operation, slice::invalid(), slice::invalid(), throw_notfound) {}
    move_result(cursor &cursor, move_operation operation, const slice &key, bool throw_notfound)
        : move_result(cursor, operation, key, slice::invalid(), throw_notfound) {}
    inline move_result(cursor &cursor, move_operation operation, const slice &key, const slice &value,
                       bool throw_notfound);
    move_result(const move_result &) noexcept = default;
    move_result &operator=(const move_result &) noexcept = default;
  };
 
  struct estimate_result : public pair {
    ptrdiff_t approximate_quantity;
    estimate_result(const cursor &cursor, move_operation operation)
        : estimate_result(cursor, operation, slice::invalid(), slice::invalid()) {}
    estimate_result(const cursor &cursor, move_operation operation, const slice &key)
        : estimate_result(cursor, operation, key, slice::invalid()) {}
    inline estimate_result(const cursor &cursor, move_operation operation, const slice &key, const slice &value);
    estimate_result(const estimate_result &) noexcept = default;
    estimate_result &operator=(const estimate_result &) noexcept = default;
  };
 
protected:
  /* fake `const`, but for specific move/get operations */
  inline bool move(move_operation operation, MDBX_val *key, MDBX_val *value, bool throw_notfound) const;
 
  inline ptrdiff_t estimate(move_operation operation, MDBX_val *key, MDBX_val *value) const;
 
public:
  template <typename CALLABLE_PREDICATE>
  bool scan(CALLABLE_PREDICATE predicate, move_operation start = first, move_operation turn = next) {
    struct wrapper : public exception_thunk {
      static int probe(void *context, MDBX_val *key, MDBX_val *value, void *arg) noexcept {
        auto thunk = static_cast<wrapper *>(context);
        assert(thunk->is_clean());
        auto &predicate = *static_cast<CALLABLE_PREDICATE *>(arg);
        try {
          return predicate(pair(*key, *value)) ? MDBX_RESULT_TRUE : MDBX_RESULT_FALSE;
        } catch (... /* capture any exception to rethrow it over C code */) {
          thunk->capture();
          return MDBX_RESULT_TRUE;
        }
      }
    } thunk;
    return error::boolean_or_throw(
        ::mdbx_cursor_scan(handle_, wrapper::probe, &thunk, MDBX_cursor_op(start), MDBX_cursor_op(turn), &predicate),
        thunk);
  }
 
  template <typename CALLABLE_PREDICATE> bool fullscan(CALLABLE_PREDICATE predicate, bool backward = false) {
    return scan(std::move(predicate), backward ? last : first, backward ? previous : next);
  }
 
  template <typename CALLABLE_PREDICATE>
  bool scan_from(CALLABLE_PREDICATE predicate, slice &from, move_operation start = key_greater_or_equal,
                 move_operation turn = next) {
    struct wrapper : public exception_thunk {
      static int probe(void *context, MDBX_val *key, MDBX_val *value, void *arg) noexcept {
        auto thunk = static_cast<wrapper *>(context);
        assert(thunk->is_clean());
        auto &predicate = *static_cast<CALLABLE_PREDICATE *>(arg);
        try {
          return predicate(pair(*key, *value)) ? MDBX_RESULT_TRUE : MDBX_RESULT_FALSE;
        } catch (... /* capture any exception to rethrow it over C code */) {
          thunk->capture();
          return MDBX_RESULT_TRUE;
        }
      }
    } thunk;
    return error::boolean_or_throw(::mdbx_cursor_scan_from(handle_, wrapper::probe, &thunk, MDBX_cursor_op(start),
                                                           &from, nullptr, MDBX_cursor_op(turn), &predicate),
                                   thunk);
  }
 
  template <typename CALLABLE_PREDICATE>
  bool scan_from(CALLABLE_PREDICATE predicate, pair &from, move_operation start = pair_greater_or_equal,
                 move_operation turn = next) {
    struct wrapper : public exception_thunk {
      static int probe(void *context, MDBX_val *key, MDBX_val *value, void *arg) noexcept {
        auto thunk = static_cast<wrapper *>(context);
        assert(thunk->is_clean());
        auto &predicate = *static_cast<CALLABLE_PREDICATE *>(arg);
        try {
          return predicate(pair(*key, *value)) ? MDBX_RESULT_TRUE : MDBX_RESULT_FALSE;
        } catch (... /* capture any exception to rethrow it over C code */) {
          thunk->capture();
          return MDBX_RESULT_TRUE;
        }
      }
    } thunk;
    return error::boolean_or_throw(::mdbx_cursor_scan_from(handle_, wrapper::probe, &thunk, MDBX_cursor_op(start),
                                                           &from.key, &from.value, MDBX_cursor_op(turn), &predicate),
                                   thunk);
  }
 
  move_result move(move_operation operation, bool throw_notfound) {
    return move_result(*this, operation, throw_notfound);
  }
  move_result move(move_operation operation, const slice &key, bool throw_notfound) {
    return move_result(*this, operation, key, slice::invalid(), throw_notfound);
  }
  move_result move(move_operation operation, const slice &key, const slice &value, bool throw_notfound) {
    return move_result(*this, operation, key, value, throw_notfound);
  }
  bool move(move_operation operation, slice &key, slice &value, bool throw_notfound) {
    return move(operation, &key, &value, throw_notfound);
  }
 
  move_result to_first(bool throw_notfound = true) { return move(first, throw_notfound); }
  move_result to_previous(bool throw_notfound = true) { return move(previous, throw_notfound); }
  move_result to_previous_last_multi(bool throw_notfound = true) {
    return move(multi_prevkey_lastvalue, throw_notfound);
  }
  move_result to_current_first_multi(bool throw_notfound = true) {
    return move(multi_currentkey_firstvalue, throw_notfound);
  }
  move_result to_current_prev_multi(bool throw_notfound = true) {
    return move(multi_currentkey_prevvalue, throw_notfound);
  }
  move_result current(bool throw_notfound = true) const { return move_result(*this, throw_notfound); }
  move_result to_current_next_multi(bool throw_notfound = true) {
    return move(multi_currentkey_nextvalue, throw_notfound);
  }
  move_result to_current_last_multi(bool throw_notfound = true) {
    return move(multi_currentkey_lastvalue, throw_notfound);
  }
  move_result to_next_first_multi(bool throw_notfound = true) { return move(multi_nextkey_firstvalue, throw_notfound); }
  move_result to_next(bool throw_notfound = true) { return move(next, throw_notfound); }
  move_result to_last(bool throw_notfound = true) { return move(last, throw_notfound); }
 
  move_result to_key_lesser_than(const slice &key, bool throw_notfound = true) {
    return move(key_lesser_than, key, throw_notfound);
  }
  move_result to_key_lesser_or_equal(const slice &key, bool throw_notfound = true) {
    return move(key_lesser_or_equal, key, throw_notfound);
  }
  move_result to_key_equal(const slice &key, bool throw_notfound = true) {
    return move(key_equal, key, throw_notfound);
  }
  move_result to_key_exact(const slice &key, bool throw_notfound = true) {
    return move(key_exact, key, throw_notfound);
  }
  move_result to_key_greater_or_equal(const slice &key, bool throw_notfound = true) {
    return move(key_greater_or_equal, key, throw_notfound);
  }
  move_result to_key_greater_than(const slice &key, bool throw_notfound = true) {
    return move(key_greater_than, key, throw_notfound);
  }
 
  move_result to_exact_key_value_lesser_than(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(multi_exactkey_value_lesser_than, key, value, throw_notfound);
  }
  move_result to_exact_key_value_lesser_or_equal(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(multi_exactkey_value_lesser_or_equal, key, value, throw_notfound);
  }
  move_result to_exact_key_value_equal(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(multi_exactkey_value_equal, key, value, throw_notfound);
  }
  move_result to_exact_key_value_greater_or_equal(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(multi_exactkey_value_greater_or_equal, key, value, throw_notfound);
  }
  move_result to_exact_key_value_greater_than(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(multi_exactkey_value_greater, key, value, throw_notfound);
  }
 
  move_result to_pair_lesser_than(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(pair_lesser_than, key, value, throw_notfound);
  }
  move_result to_pair_lesser_or_equal(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(pair_lesser_or_equal, key, value, throw_notfound);
  }
  move_result to_pair_equal(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(pair_equal, key, value, throw_notfound);
  }
  move_result to_pair_exact(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(pair_exact, key, value, throw_notfound);
  }
  move_result to_pair_greater_or_equal(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(pair_greater_or_equal, key, value, throw_notfound);
  }
  move_result to_pair_greater_than(const slice &key, const slice &value, bool throw_notfound = true) {
    return move(pair_greater_than, key, value, throw_notfound);
  }
 
  inline bool seek(const slice &key);
  inline move_result find(const slice &key, bool throw_notfound = true);
  inline move_result lower_bound(const slice &key, bool throw_notfound = false);
  inline move_result upper_bound(const slice &key, bool throw_notfound = false);

  inline size_t count_multivalue() const;
 
  inline move_result find_multivalue(const slice &key, const slice &value, bool throw_notfound = true);
  inline move_result lower_bound_multivalue(const slice &key, const slice &value, bool throw_notfound = false);
  inline move_result upper_bound_multivalue(const slice &key, const slice &value, bool throw_notfound = false);
 
  inline move_result seek_multiple_samelength(const slice &key, bool throw_notfound = true) {
    return move(seek_and_batch_samelength, key, throw_notfound);
  }
 
  inline move_result get_multiple_samelength(bool throw_notfound = false) {
    return move(batch_samelength, throw_notfound);
  }
 
  inline move_result next_multiple_samelength(bool throw_notfound = false) {
    return move(batch_samelength_next, throw_notfound);
  }
 
  inline move_result previous_multiple_samelength(bool throw_notfound = false) {
    return move(batch_samelength_previous, throw_notfound);
  }
 
  inline bool eof() const;
  inline bool on_first() const;
  inline bool on_last() const;
  inline bool on_first_multival() const;
  inline bool on_last_multival() const;
  inline estimate_result estimate(const slice &key, const slice &value) const;
  inline estimate_result estimate(const slice &key) const;
  inline estimate_result estimate(move_operation operation) const;
  inline estimate_result estimate(move_operation operation, slice &key) const;
 
  //----------------------------------------------------------------------------

  inline void renew(::mdbx::txn &txn);

  inline void bind(::mdbx::txn &txn, ::mdbx::map_handle map_handle);

  inline void unbind();

  inline ::mdbx::txn txn() const;
  inline map_handle map() const;
 
  inline operator ::mdbx::txn() const { return txn(); }
  inline operator ::mdbx::map_handle() const { return map(); }
 
  inline MDBX_error_t put(const slice &key, slice *value, MDBX_put_flags_t flags) noexcept;
  inline void put(const slice &key, slice value, put_mode mode);
  inline void insert(const slice &key, slice value);
  inline value_result try_insert(const slice &key, slice value);
  inline slice insert_reserve(const slice &key, size_t value_length);
  inline value_result try_insert_reserve(const slice &key, size_t value_length);
 
  inline void upsert(const slice &key, const slice &value);
  inline slice upsert_reserve(const slice &key, size_t value_length);

  void update_current(const slice &value);
  slice reverse_current(size_t value_length);
 
  inline void update(const slice &key, const slice &value);
  inline bool try_update(const slice &key, const slice &value);
  inline slice update_reserve(const slice &key, size_t value_length);
  inline value_result try_update_reserve(const slice &key, size_t value_length);
 
  void put(const pair &kv, put_mode mode) { return put(kv.key, kv.value, mode); }
  void insert(const pair &kv) { return insert(kv.key, kv.value); }
  value_result try_insert(const pair &kv) { return try_insert(kv.key, kv.value); }
  void upsert(const pair &kv) { return upsert(kv.key, kv.value); }

  inline bool erase(bool whole_multivalue = false);

  inline bool erase(const slice &key, bool whole_multivalue = true);

  inline bool erase(const slice &key, const slice &value);
 
  inline size_t put_multiple_samelength(const slice &key, const size_t value_length, const void *values_array,
                                        size_t values_count, put_mode mode, bool allow_partial = false);
  template <typename VALUE>
  size_t put_multiple_samelength(const slice &key, const VALUE *values_array, size_t values_count, put_mode mode,
                                 bool allow_partial = false) {
    static_assert(::std::is_standard_layout<VALUE>::value && !::std::is_pointer<VALUE>::value &&
                      !::std::is_array<VALUE>::value,
                  "Must be a standard layout type!");
    return put_multiple_samelength(key, sizeof(VALUE), values_array, values_count, mode, allow_partial);
  }
  template <typename VALUE>
  void put_multiple_samelength(const slice &key, const ::std::vector<VALUE> &vector, put_mode mode) {
    put_multiple_samelength(key, vector.data(), vector.size(), mode);
  }
};

class LIBMDBX_API_TYPE cursor_managed : public cursor {
  using inherited = cursor;
  friend class txn;
  MDBX_CXX11_CONSTEXPR cursor_managed(MDBX_cursor *ptr) noexcept : inherited(ptr) {}
 
public:
  cursor_managed(void *your_context = nullptr) : cursor_managed(::mdbx_cursor_create(your_context)) {
    if (MDBX_UNLIKELY(!handle_))
      MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_ENOMEM);
  }

  inline void close() {
    error::success_or_throw(::mdbx_cursor_close2(handle_));
    handle_ = nullptr;
  }
 
  cursor_managed(cursor_managed &&) = default;
  cursor_managed &operator=(cursor_managed &&other) noexcept {
    if (MDBX_UNLIKELY(handle_))
      MDBX_CXX20_UNLIKELY {
        assert(handle_ != other.handle_);
        close();
      }
    inherited::operator=(std::move(other));
    return *this;
  }
 
  inline MDBX_cursor *withdraw_handle() noexcept {
    MDBX_cursor *handle = handle_;
    handle_ = nullptr;
    return handle;
  }
 
  cursor_managed(const cursor_managed &) = delete;
  cursor_managed &operator=(const cursor_managed &) = delete;
  ~cursor_managed() noexcept { ::mdbx_cursor_close(handle_); }
};
 
//==============================================================================
//
// Inline body of the libmdbx C++ API
//
 
MDBX_CXX11_CONSTEXPR const version_info &get_version() noexcept { return ::mdbx_version; }
MDBX_CXX11_CONSTEXPR const build_info &get_build() noexcept { return ::mdbx_build; }
 
static MDBX_CXX17_CONSTEXPR size_t strlen(const char *c_str) noexcept {
#if defined(__cpp_lib_is_constant_evaluated) && __cpp_lib_is_constant_evaluated >= 201811L
  if (::std::is_constant_evaluated()) {
    for (size_t i = 0; c_str; ++i)
      if (!c_str[i])
        return i;
    return 0;
  }
#endif /* __cpp_lib_is_constant_evaluated >= 201811 */
#if defined(__cpp_lib_string_view) && __cpp_lib_string_view >= 201606L
  return c_str ? ::std::string_view(c_str).length() : 0;
#else
  return c_str ? ::std::strlen(c_str) : 0;
#endif
}
 
MDBX_MAYBE_UNUSED static MDBX_CXX20_CONSTEXPR void *memcpy(void *dest, const void *src, size_t bytes) noexcept {
#if defined(__cpp_lib_is_constant_evaluated) && __cpp_lib_is_constant_evaluated >= 201811L
  if (::std::is_constant_evaluated()) {
    for (size_t i = 0; i < bytes; ++i)
      static_cast<byte *>(dest)[i] = static_cast<const byte *>(src)[i];
    return dest;
  } else
#endif /* __cpp_lib_is_constant_evaluated >= 201811 */
    return ::std::memcpy(dest, src, bytes);
}
 
static MDBX_CXX20_CONSTEXPR int memcmp(const void *a, const void *b, size_t bytes) noexcept {
#if defined(__cpp_lib_is_constant_evaluated) && __cpp_lib_is_constant_evaluated >= 201811L
  if (::std::is_constant_evaluated()) {
    for (size_t i = 0; i < bytes; ++i) {
      const int diff = int(static_cast<const byte *>(a)[i]) - int(static_cast<const byte *>(b)[i]);
      if (diff)
        return diff;
    }
    return 0;
  } else
#endif /* __cpp_lib_is_constant_evaluated >= 201811 */
    return ::std::memcmp(a, b, bytes);
}
 
//------------------------------------------------------------------------------
 
MDBX_CXX11_CONSTEXPR map_handle::info::info(map_handle::flags flags, map_handle::state state) noexcept
    : flags(flags), state(state) {}
 
MDBX_CXX11_CONSTEXPR_ENUM mdbx::key_mode map_handle::info::key_mode() const noexcept {
  return ::mdbx::key_mode(flags & (MDBX_REVERSEKEY | MDBX_INTEGERKEY));
}
 
MDBX_CXX11_CONSTEXPR_ENUM mdbx::value_mode map_handle::info::value_mode() const noexcept {
  return ::mdbx::value_mode(flags & (MDBX_DUPSORT | MDBX_REVERSEDUP | MDBX_DUPFIXED | MDBX_INTEGERDUP));
}
 
inline bool exception_thunk::is_clean() const noexcept { return !captured_; }
 
inline void exception_thunk::capture() noexcept {
  assert(is_clean());
  captured_ = ::std::current_exception();
}
 
inline void exception_thunk::rethrow_captured() const {
  if (captured_)
    MDBX_CXX20_UNLIKELY ::std::rethrow_exception(captured_);
}
 
//------------------------------------------------------------------------------
 
MDBX_CXX11_CONSTEXPR error::error(MDBX_error_t error_code) noexcept : code_(error_code) {}
 
inline error &error::operator=(MDBX_error_t error_code) noexcept {
  code_ = error_code;
  return *this;
}
 
MDBX_CXX11_CONSTEXPR bool operator==(const error &a, const error &b) noexcept { return a.code_ == b.code_; }
 
MDBX_CXX11_CONSTEXPR bool operator!=(const error &a, const error &b) noexcept { return !(a == b); }
 
MDBX_CXX11_CONSTEXPR bool error::is_success() const noexcept { return code_ == MDBX_SUCCESS; }
 
MDBX_CXX11_CONSTEXPR bool error::is_result_true() const noexcept { return code_ == MDBX_RESULT_FALSE; }
 
MDBX_CXX11_CONSTEXPR bool error::is_result_false() const noexcept { return code_ == MDBX_RESULT_TRUE; }
 
MDBX_CXX11_CONSTEXPR bool error::is_failure() const noexcept {
  return code_ != MDBX_SUCCESS && code_ != MDBX_RESULT_TRUE;
}
 
MDBX_CXX11_CONSTEXPR MDBX_error_t error::code() const noexcept { return code_; }
 
MDBX_CXX11_CONSTEXPR bool error::is_mdbx_error() const noexcept {
  return (code() >= MDBX_FIRST_LMDB_ERRCODE && code() <= MDBX_LAST_LMDB_ERRCODE) ||
         (code() >= MDBX_FIRST_ADDED_ERRCODE && code() <= MDBX_LAST_ADDED_ERRCODE);
}
 
inline void error::throw_exception(int error_code) {
  const error trouble(static_cast<MDBX_error_t>(error_code));
  trouble.throw_exception();
}
 
inline void error::throw_on_failure() const {
  if (MDBX_UNLIKELY(is_failure()))
    MDBX_CXX20_UNLIKELY throw_exception();
}
 
inline void error::success_or_throw() const {
  if (MDBX_UNLIKELY(!is_success()))
    MDBX_CXX20_UNLIKELY throw_exception();
}
 
inline void error::success_or_throw(const exception_thunk &thunk) const {
  assert(thunk.is_clean() || code() != MDBX_SUCCESS);
  if (MDBX_UNLIKELY(!is_success())) {
    MDBX_CXX20_UNLIKELY if (MDBX_UNLIKELY(!thunk.is_clean())) thunk.rethrow_captured();
    else throw_exception();
  }
}
 
inline void error::panic_on_failure(const char *context_where, const char *func_who) const noexcept {
  if (MDBX_UNLIKELY(is_failure()))
    MDBX_CXX20_UNLIKELY panic(context_where, func_who);
}
 
inline void error::success_or_panic(const char *context_where, const char *func_who) const noexcept {
  if (MDBX_UNLIKELY(!is_success()))
    MDBX_CXX20_UNLIKELY panic(context_where, func_who);
}
 
inline void error::throw_on_nullptr(const void *ptr, MDBX_error_t error_code) {
  if (MDBX_UNLIKELY(ptr == nullptr))
    MDBX_CXX20_UNLIKELY error(error_code).throw_exception();
}
 
inline void error::throw_on_failure(int error_code) {
  error rc(static_cast<MDBX_error_t>(error_code));
  rc.throw_on_failure();
}
 
inline void error::success_or_throw(MDBX_error_t error_code) {
  error rc(error_code);
  rc.success_or_throw();
}
 
inline bool error::boolean_or_throw(int error_code) {
  switch (error_code) {
  case MDBX_RESULT_FALSE:
    return false;
  case MDBX_RESULT_TRUE:
    return true;
  default:
    MDBX_CXX20_UNLIKELY throw_exception(error_code);
  }
}
 
inline void error::success_or_throw(int error_code, const exception_thunk &thunk) {
  error rc(static_cast<MDBX_error_t>(error_code));
  rc.success_or_throw(thunk);
}
 
inline void error::panic_on_failure(int error_code, const char *context_where, const char *func_who) noexcept {
  error rc(static_cast<MDBX_error_t>(error_code));
  rc.panic_on_failure(context_where, func_who);
}
 
inline void error::success_or_panic(int error_code, const char *context_where, const char *func_who) noexcept {
  error rc(static_cast<MDBX_error_t>(error_code));
  rc.success_or_panic(context_where, func_who);
}
 
inline bool error::boolean_or_throw(int error_code, const exception_thunk &thunk) {
  if (MDBX_UNLIKELY(!thunk.is_clean()))
    MDBX_CXX20_UNLIKELY thunk.rethrow_captured();
  return boolean_or_throw(error_code);
}
 
MDBX_CXX11_CONSTEXPR slice::slice() noexcept : ::MDBX_val({nullptr, 0}) {}
 
MDBX_CXX14_CONSTEXPR slice::slice(const void *ptr, size_t bytes)
    : ::MDBX_val({const_cast<void *>(ptr), check_length(bytes)}) {}
 
MDBX_CXX14_CONSTEXPR slice::slice(const void *begin, const void *end)
    : slice(begin, static_cast<const byte *>(end) - static_cast<const byte *>(begin)) {}
 
MDBX_CXX17_CONSTEXPR slice::slice(const char *c_str) : slice(c_str, strlen(c_str)) {}
 
MDBX_CXX14_CONSTEXPR slice::slice(const MDBX_val &src) : slice(src.iov_base, src.iov_len) {}
 
MDBX_CXX14_CONSTEXPR slice::slice(MDBX_val &&src) : slice(src) { src.iov_base = nullptr; }
 
MDBX_CXX14_CONSTEXPR slice::slice(slice &&src) noexcept : slice(src) { src.invalidate(); }
 
inline slice &slice::assign(const void *ptr, size_t bytes) {
  iov_base = const_cast<void *>(ptr);
  iov_len = check_length(bytes);
  return *this;
}
 
inline slice &slice::assign(const slice &src) noexcept {
  iov_base = src.iov_base;
  iov_len = src.iov_len;
  return *this;
}
 
inline slice &slice::assign(const ::MDBX_val &src) { return assign(src.iov_base, src.iov_len); }
 
slice &slice::assign(slice &&src) noexcept {
  assign(src);
  src.invalidate();
  return *this;
}
 
inline slice &slice::assign(::MDBX_val &&src) {
  assign(src.iov_base, src.iov_len);
  src.iov_base = nullptr;
  return *this;
}
 
inline slice &slice::assign(const void *begin, const void *end) {
  return assign(begin, static_cast<const byte *>(end) - static_cast<const byte *>(begin));
}
 
inline slice &slice::assign(const char *c_str) { return assign(c_str, strlen(c_str)); }
 
inline slice &slice::operator=(slice &&src) noexcept { return assign(::std::move(src)); }
 
inline slice &slice::operator=(::MDBX_val &&src) { return assign(::std::move(src)); }
 
MDBX_CXX11_CONSTEXPR const byte *slice::byte_ptr() const noexcept { return static_cast<const byte *>(iov_base); }
 
MDBX_CXX11_CONSTEXPR const byte *slice::end_byte_ptr() const noexcept { return byte_ptr() + length(); }
 
MDBX_CXX11_CONSTEXPR byte *slice::byte_ptr() noexcept { return static_cast<byte *>(iov_base); }
 
MDBX_CXX11_CONSTEXPR byte *slice::end_byte_ptr() noexcept { return byte_ptr() + length(); }
 
MDBX_CXX11_CONSTEXPR const char *slice::char_ptr() const noexcept { return static_cast<const char *>(iov_base); }
 
MDBX_CXX11_CONSTEXPR const char *slice::end_char_ptr() const noexcept { return char_ptr() + length(); }
 
MDBX_CXX11_CONSTEXPR char *slice::char_ptr() noexcept { return static_cast<char *>(iov_base); }
 
MDBX_CXX11_CONSTEXPR char *slice::end_char_ptr() noexcept { return char_ptr() + length(); }
 
MDBX_CXX11_CONSTEXPR const void *slice::data() const noexcept { return iov_base; }
 
MDBX_CXX11_CONSTEXPR const void *slice::end() const noexcept { return static_cast<const void *>(end_byte_ptr()); }
 
MDBX_CXX11_CONSTEXPR void *slice::data() noexcept { return iov_base; }
 
MDBX_CXX11_CONSTEXPR void *slice::end() noexcept { return static_cast<void *>(end_byte_ptr()); }
 
MDBX_CXX11_CONSTEXPR size_t slice::length() const noexcept { return iov_len; }
 
MDBX_CXX14_CONSTEXPR slice &slice::set_length(size_t bytes) {
  iov_len = check_length(bytes);
  return *this;
}
 
MDBX_CXX14_CONSTEXPR slice &slice::set_end(const void *ptr) {
  MDBX_CONSTEXPR_ASSERT(static_cast<const char *>(ptr) >= char_ptr());
  return set_length(static_cast<const char *>(ptr) - char_ptr());
}
 
MDBX_CXX11_CONSTEXPR bool slice::empty() const noexcept { return length() == 0; }
 
MDBX_CXX11_CONSTEXPR bool slice::is_null() const noexcept { return data() == nullptr; }
 
MDBX_CXX11_CONSTEXPR size_t slice::size() const noexcept { return length(); }
 
MDBX_CXX11_CONSTEXPR slice::operator bool() const noexcept { return !is_null(); }
 
MDBX_CXX14_CONSTEXPR void slice::invalidate() noexcept { iov_base = nullptr; }
 
MDBX_CXX14_CONSTEXPR void slice::clear() noexcept {
  iov_base = nullptr;
  iov_len = 0;
}
 
inline void slice::remove_prefix(size_t n) noexcept {
  assert(n <= size());
  iov_base = static_cast<byte *>(iov_base) + n;
  iov_len -= n;
}
 
inline void slice::safe_remove_prefix(size_t n) {
  if (MDBX_UNLIKELY(n > size()))
    MDBX_CXX20_UNLIKELY throw_out_range();
  remove_prefix(n);
}
 
inline void slice::remove_suffix(size_t n) noexcept {
  assert(n <= size());
  iov_len -= n;
}
 
inline void slice::safe_remove_suffix(size_t n) {
  if (MDBX_UNLIKELY(n > size()))
    MDBX_CXX20_UNLIKELY throw_out_range();
  remove_suffix(n);
}
 
MDBX_CXX14_CONSTEXPR bool slice::starts_with(const slice &prefix) const noexcept {
  return length() >= prefix.length() && memcmp(data(), prefix.data(), prefix.length()) == 0;
}
 
MDBX_CXX14_CONSTEXPR bool slice::ends_with(const slice &suffix) const noexcept {
  return length() >= suffix.length() &&
         memcmp(byte_ptr() + length() - suffix.length(), suffix.data(), suffix.length()) == 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR size_t slice::hash_value() const noexcept {
  size_t h = length() * 3977471;
  for (size_t i = 0; i < length(); ++i)
    h = (h ^ static_cast<const uint8_t *>(data())[i]) * 1664525 + 1013904223;
  return h ^ 3863194411 * (h >> 11);
}
 
MDBX_CXX11_CONSTEXPR byte slice::operator[](size_t n) const noexcept {
  MDBX_CONSTEXPR_ASSERT(n < size());
  return byte_ptr()[n];
}
 
MDBX_CXX11_CONSTEXPR byte slice::at(size_t n) const {
  if (MDBX_UNLIKELY(n >= size()))
    MDBX_CXX20_UNLIKELY throw_out_range();
  return byte_ptr()[n];
}
 
MDBX_CXX14_CONSTEXPR slice slice::head(size_t n) const noexcept {
  MDBX_CONSTEXPR_ASSERT(n <= size());
  return slice(data(), n);
}
 
MDBX_CXX14_CONSTEXPR slice slice::tail(size_t n) const noexcept {
  MDBX_CONSTEXPR_ASSERT(n <= size());
  return slice(char_ptr() + size() - n, n);
}
 
MDBX_CXX14_CONSTEXPR slice slice::middle(size_t from, size_t n) const noexcept {
  MDBX_CONSTEXPR_ASSERT(from + n <= size());
  return slice(char_ptr() + from, n);
}
 
MDBX_CXX14_CONSTEXPR slice slice::safe_head(size_t n) const {
  if (MDBX_UNLIKELY(n > size()))
    MDBX_CXX20_UNLIKELY throw_out_range();
  return head(n);
}
 
MDBX_CXX14_CONSTEXPR slice slice::safe_tail(size_t n) const {
  if (MDBX_UNLIKELY(n > size()))
    MDBX_CXX20_UNLIKELY throw_out_range();
  return tail(n);
}
 
MDBX_CXX14_CONSTEXPR slice slice::safe_middle(size_t from, size_t n) const {
  if (MDBX_UNLIKELY(n > max_length))
    MDBX_CXX20_UNLIKELY throw_max_length_exceeded();
  if (MDBX_UNLIKELY(from + n > size()))
    MDBX_CXX20_UNLIKELY throw_out_range();
  return middle(from, n);
}
 
MDBX_CXX14_CONSTEXPR intptr_t slice::compare_fast(const slice &a, const slice &b) noexcept {
  const intptr_t diff = intptr_t(a.length()) - intptr_t(b.length());
  return diff                                                     ? diff
         : MDBX_UNLIKELY(a.length() == 0 || a.data() == b.data()) ? 0
                                                                  : memcmp(a.data(), b.data(), a.length());
}
 
MDBX_CXX14_CONSTEXPR intptr_t slice::compare_lexicographically(const slice &a, const slice &b) noexcept {
  const size_t shortest = ::std::min(a.length(), b.length());
  if (MDBX_LIKELY(shortest > 0))
    MDBX_CXX20_LIKELY {
      const intptr_t diff = memcmp(a.data(), b.data(), shortest);
      if (MDBX_LIKELY(diff != 0))
        MDBX_CXX20_LIKELY return diff;
    }
  return intptr_t(a.length()) - intptr_t(b.length());
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator==(const slice &a, const slice &b) noexcept {
  return slice::compare_fast(a, b) == 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator<(const slice &a, const slice &b) noexcept {
  return slice::compare_lexicographically(a, b) < 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator>(const slice &a, const slice &b) noexcept {
  return slice::compare_lexicographically(a, b) > 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator<=(const slice &a, const slice &b) noexcept {
  return slice::compare_lexicographically(a, b) <= 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator>=(const slice &a, const slice &b) noexcept {
  return slice::compare_lexicographically(a, b) >= 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator!=(const slice &a, const slice &b) noexcept {
  return slice::compare_fast(a, b) != 0;
}
 
#if defined(__cpp_impl_three_way_comparison) && __cpp_impl_three_way_comparison >= 201907L
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR auto operator<=>(const slice &a, const slice &b) noexcept {
  return slice::compare_lexicographically(a, b);
}
#endif /* __cpp_impl_three_way_comparison */
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
MDBX_CXX20_CONSTEXPR buffer<ALLOCATOR, CAPACITY_POLICY>::buffer(const struct slice &src, bool make_reference,
                                                                const allocator_type &alloc)
    : inherited(src), silo_(alloc) {
  if (!make_reference)
    insulate();
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY>::buffer(const txn &transaction, const struct slice &src,
                                                  const allocator_type &alloc)
    : buffer(src, !transaction.is_dirty(src.data()), alloc) {}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
inline ::std::ostream &operator<<(::std::ostream &out, const buffer<ALLOCATOR, CAPACITY_POLICY> &it) {
  return (it.is_freestanding() ? out << "buf-" << it.headroom() << "." << it.tailroom() : out << "ref-") << it.slice();
}
 
#if !(defined(__MINGW__) || defined(__MINGW32__) || defined(__MINGW64__)) || defined(LIBMDBX_EXPORTS)
MDBX_EXTERN_API_TEMPLATE(LIBMDBX_API_TYPE, buffer<legacy_allocator, default_capacity_policy>);
 
#if MDBX_CXX_HAS_POLYMORPHIC_ALLOCATOR
MDBX_EXTERN_API_TEMPLATE(LIBMDBX_API_TYPE, buffer<polymorphic_allocator, default_capacity_policy>);
#endif /* MDBX_CXX_HAS_POLYMORPHIC_ALLOCATOR */
#endif /* !MinGW || MDBX_EXPORTS */

using default_buffer = buffer<default_allocator, default_capacity_policy>;
 
//------------------------------------------------------------------------------
 
template <class ALLOCATOR, class CAPACITY_POLICY, MDBX_CXX20_CONCEPT(MutableByteProducer, PRODUCER)>
inline buffer<ALLOCATOR, CAPACITY_POLICY> make_buffer(PRODUCER &producer, const ALLOCATOR &alloc) {
  if (MDBX_LIKELY(!producer.is_empty()))
    MDBX_CXX20_LIKELY {
      buffer<ALLOCATOR, CAPACITY_POLICY> result(producer.envisage_result_length(), alloc);
      result.set_end(producer.write_bytes(result.end_char_ptr(), result.tailroom()));
      return result;
    }
  return buffer<ALLOCATOR, CAPACITY_POLICY>(alloc);
}
 
template <class ALLOCATOR, class CAPACITY_POLICY, MDBX_CXX20_CONCEPT(ImmutableByteProducer, PRODUCER)>
inline buffer<ALLOCATOR, CAPACITY_POLICY> make_buffer(const PRODUCER &producer, const ALLOCATOR &alloc) {
  if (MDBX_LIKELY(!producer.is_empty()))
    MDBX_CXX20_LIKELY {
      buffer<ALLOCATOR, CAPACITY_POLICY> result(producer.envisage_result_length(), alloc);
      result.set_end(producer.write_bytes(result.end_char_ptr(), result.tailroom()));
      return result;
    }
  return buffer<ALLOCATOR, CAPACITY_POLICY>(alloc);
}
 
template <class ALLOCATOR, MDBX_CXX20_CONCEPT(MutableByteProducer, PRODUCER)>
inline string<ALLOCATOR> make_string(PRODUCER &producer, const ALLOCATOR &alloc) {
  string<ALLOCATOR> result(alloc);
  if (MDBX_LIKELY(!producer.is_empty()))
    MDBX_CXX20_LIKELY {
      result.resize(producer.envisage_result_length());
      result.resize(producer.write_bytes(const_cast<char *>(result.data()), result.capacity()) - result.data());
    }
  return result;
}
 
template <class ALLOCATOR, MDBX_CXX20_CONCEPT(ImmutableByteProducer, PRODUCER)>
inline string<ALLOCATOR> make_string(const PRODUCER &producer, const ALLOCATOR &alloc) {
  string<ALLOCATOR> result(alloc);
  if (MDBX_LIKELY(!producer.is_empty()))
    MDBX_CXX20_LIKELY {
      result.resize(producer.envisage_result_length());
      result.resize(producer.write_bytes(const_cast<char *>(result.data()), result.capacity()) - result.data());
    }
  return result;
}
 
template <class ALLOCATOR> string<ALLOCATOR> to_hex::as_string(const ALLOCATOR &alloc) const {
  return make_string<ALLOCATOR>(*this, alloc);
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
buffer<ALLOCATOR, CAPACITY_POLICY> to_hex::as_buffer(const ALLOCATOR &alloc) const {
  return make_buffer<ALLOCATOR, CAPACITY_POLICY>(*this, alloc);
}
 
template <class ALLOCATOR> string<ALLOCATOR> to_base58::as_string(const ALLOCATOR &alloc) const {
  return make_string<ALLOCATOR>(*this, alloc);
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
buffer<ALLOCATOR, CAPACITY_POLICY> to_base58::as_buffer(const ALLOCATOR &alloc) const {
  return make_buffer<ALLOCATOR, CAPACITY_POLICY>(*this, alloc);
}
 
template <class ALLOCATOR> string<ALLOCATOR> to_base64::as_string(const ALLOCATOR &alloc) const {
  return make_string<ALLOCATOR>(*this, alloc);
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
buffer<ALLOCATOR, CAPACITY_POLICY> to_base64::as_buffer(const ALLOCATOR &alloc) const {
  return make_buffer<ALLOCATOR, CAPACITY_POLICY>(*this, alloc);
}
 
template <class ALLOCATOR> string<ALLOCATOR> from_hex::as_string(const ALLOCATOR &alloc) const {
  return make_string<ALLOCATOR>(*this, alloc);
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
buffer<ALLOCATOR, CAPACITY_POLICY> from_hex::as_buffer(const ALLOCATOR &alloc) const {
  return make_buffer<ALLOCATOR, CAPACITY_POLICY>(*this, alloc);
}
 
template <class ALLOCATOR> string<ALLOCATOR> from_base58::as_string(const ALLOCATOR &alloc) const {
  return make_string<ALLOCATOR>(*this, alloc);
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
buffer<ALLOCATOR, CAPACITY_POLICY> from_base58::as_buffer(const ALLOCATOR &alloc) const {
  return make_buffer<ALLOCATOR, CAPACITY_POLICY>(*this, alloc);
}
 
template <class ALLOCATOR> string<ALLOCATOR> from_base64::as_string(const ALLOCATOR &alloc) const {
  return make_string<ALLOCATOR>(*this, alloc);
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
buffer<ALLOCATOR, CAPACITY_POLICY> from_base64::as_buffer(const ALLOCATOR &alloc) const {
  return make_buffer<ALLOCATOR, CAPACITY_POLICY>(*this, alloc);
}
 
template <class ALLOCATOR>
inline string<ALLOCATOR> slice::as_hex_string(bool uppercase, unsigned wrap_width, const ALLOCATOR &alloc) const {
  return to_hex(*this, uppercase, wrap_width).as_string<ALLOCATOR>(alloc);
}
 
template <class ALLOCATOR>
inline string<ALLOCATOR> slice::as_base58_string(unsigned wrap_width, const ALLOCATOR &alloc) const {
  return to_base58(*this, wrap_width).as_string<ALLOCATOR>(alloc);
}
 
template <class ALLOCATOR>
inline string<ALLOCATOR> slice::as_base64_string(unsigned wrap_width, const ALLOCATOR &alloc) const {
  return to_base64(*this, wrap_width).as_string<ALLOCATOR>(alloc);
}
 
template <class ALLOCATOR, class CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY> slice::encode_hex(bool uppercase, unsigned wrap_width,
                                                            const ALLOCATOR &alloc) const {
  return to_hex(*this, uppercase, wrap_width).as_buffer<ALLOCATOR, CAPACITY_POLICY>(alloc);
}
 
template <class ALLOCATOR, class CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY> slice::encode_base58(unsigned wrap_width, const ALLOCATOR &alloc) const {
  return to_base58(*this, wrap_width).as_buffer<ALLOCATOR, CAPACITY_POLICY>(alloc);
}
 
template <class ALLOCATOR, class CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY> slice::encode_base64(unsigned wrap_width, const ALLOCATOR &alloc) const {
  return to_base64(*this, wrap_width).as_buffer<ALLOCATOR, CAPACITY_POLICY>(alloc);
}
 
template <class ALLOCATOR, class CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY> slice::hex_decode(bool ignore_spaces, const ALLOCATOR &alloc) const {
  return from_hex(*this, ignore_spaces).as_buffer<ALLOCATOR, CAPACITY_POLICY>(alloc);
}
 
template <class ALLOCATOR, class CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY> slice::base58_decode(bool ignore_spaces, const ALLOCATOR &alloc) const {
  return from_base58(*this, ignore_spaces).as_buffer<ALLOCATOR, CAPACITY_POLICY>(alloc);
}
 
template <class ALLOCATOR, class CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY> slice::base64_decode(bool ignore_spaces, const ALLOCATOR &alloc) const {
  return from_base64(*this, ignore_spaces).as_buffer<ALLOCATOR, CAPACITY_POLICY>(alloc);
}
 
//------------------------------------------------------------------------------
 
MDBX_CXX14_CONSTEXPR intptr_t pair::compare_fast(const pair &a, const pair &b) noexcept {
  const auto diff = slice::compare_fast(a.key, b.key);
  return diff ? diff : slice::compare_fast(a.value, b.value);
}
 
MDBX_CXX14_CONSTEXPR intptr_t pair::compare_lexicographically(const pair &a, const pair &b) noexcept {
  const auto diff = slice::compare_lexicographically(a.key, b.key);
  return diff ? diff : slice::compare_lexicographically(a.value, b.value);
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator==(const pair &a, const pair &b) noexcept {
  return a.key.length() == b.key.length() && a.value.length() == b.value.length() &&
         memcmp(a.key.data(), b.key.data(), a.key.length()) == 0 &&
         memcmp(a.value.data(), b.value.data(), a.value.length()) == 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator<(const pair &a, const pair &b) noexcept {
  return pair::compare_lexicographically(a, b) < 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator>(const pair &a, const pair &b) noexcept {
  return pair::compare_lexicographically(a, b) > 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator<=(const pair &a, const pair &b) noexcept {
  return pair::compare_lexicographically(a, b) <= 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator>=(const pair &a, const pair &b) noexcept {
  return pair::compare_lexicographically(a, b) >= 0;
}
 
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR bool operator!=(const pair &a, const pair &b) noexcept {
  return a.key.length() != b.key.length() || a.value.length() != b.value.length() ||
         memcmp(a.key.data(), b.key.data(), a.key.length()) != 0 ||
         memcmp(a.value.data(), b.value.data(), a.value.length()) != 0;
}
 
#if defined(__cpp_impl_three_way_comparison) && __cpp_impl_three_way_comparison >= 201907L
MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX14_CONSTEXPR auto operator<=>(const pair &a, const pair &b) noexcept {
  return pair::compare_lexicographically(a, b);
}
#endif /* __cpp_impl_three_way_comparison */

template <typename BUFFER>
using buffer_pair = buffer_pair_spec<typename BUFFER::allocator_type, typename BUFFER::reservation_policy>;

using default_buffer_pair = buffer_pair<default_buffer>;
 
//------------------------------------------------------------------------------
 
inline ::std::ostream &operator<<(::std::ostream &out, const to_hex &wrapper) { return wrapper.output(out); }
inline ::std::ostream &operator<<(::std::ostream &out, const to_base58 &wrapper) { return wrapper.output(out); }
inline ::std::ostream &operator<<(::std::ostream &out, const to_base64 &wrapper) { return wrapper.output(out); }
 
MDBX_NOTHROW_PURE_FUNCTION inline bool slice::is_hex(bool ignore_spaces) const noexcept {
  return !from_hex(*this, ignore_spaces).is_erroneous();
}
 
MDBX_NOTHROW_PURE_FUNCTION inline bool slice::is_base58(bool ignore_spaces) const noexcept {
  return !from_base58(*this, ignore_spaces).is_erroneous();
}
 
MDBX_NOTHROW_PURE_FUNCTION inline bool slice::is_base64(bool ignore_spaces) const noexcept {
  return !from_base64(*this, ignore_spaces).is_erroneous();
}
 
//------------------------------------------------------------------------------
 
MDBX_CXX11_CONSTEXPR env::env(MDBX_env *ptr) noexcept : handle_(ptr) {}
 
inline env &env::operator=(env &&other) noexcept {
  handle_ = other.handle_;
  other.handle_ = nullptr;
  return *this;
}
 
inline env::env(env &&other) noexcept : handle_(other.handle_) { other.handle_ = nullptr; }
 
inline env::~env() noexcept {
#ifndef NDEBUG
  handle_ = reinterpret_cast<MDBX_env *>(uintptr_t(0xDeadBeef));
#endif
}
 
MDBX_CXX14_CONSTEXPR env::operator bool() const noexcept { return handle_ != nullptr; }
 
MDBX_CXX14_CONSTEXPR env::operator const MDBX_env *() const { return handle_; }
 
MDBX_CXX14_CONSTEXPR env::operator MDBX_env *() { return handle_; }
 
MDBX_CXX11_CONSTEXPR bool operator==(const env &a, const env &b) noexcept { return a.handle_ == b.handle_; }
 
MDBX_CXX11_CONSTEXPR bool operator!=(const env &a, const env &b) noexcept { return a.handle_ != b.handle_; }
 
inline env::geometry &env::geometry::make_fixed(intptr_t size) noexcept {
  size_lower = size_now = size_upper = size;
  growth_step = shrink_threshold = 0;
  return *this;
}
 
inline env::geometry &env::geometry::make_dynamic(intptr_t lower, intptr_t upper) noexcept {
  size_now = size_lower = lower;
  size_upper = upper;
  growth_step = shrink_threshold = default_value;
  return *this;
}
 
inline env::reclaiming_options env::operate_parameters::reclaiming_from_flags(MDBX_env_flags_t flags) noexcept {
  return reclaiming_options(flags);
}
 
inline env::operate_options env::operate_parameters::options_from_flags(MDBX_env_flags_t flags) noexcept {
  return operate_options(flags);
}
 
inline size_t env::limits::pagesize_min() noexcept { return MDBX_MIN_PAGESIZE; }
 
inline size_t env::limits::pagesize_max() noexcept { return MDBX_MAX_PAGESIZE; }
 
inline size_t env::limits::dbsize_min(intptr_t pagesize) {
  const intptr_t result = mdbx_limits_dbsize_min(pagesize);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::dbsize_max(intptr_t pagesize) {
  const intptr_t result = mdbx_limits_dbsize_max(pagesize);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::key_min(MDBX_db_flags_t flags) noexcept { return (flags & MDBX_INTEGERKEY) ? 4 : 0; }
 
inline size_t env::limits::key_min(key_mode mode) noexcept { return key_min(MDBX_db_flags_t(mode)); }
 
inline size_t env::limits::key_max(intptr_t pagesize, MDBX_db_flags_t flags) {
  const intptr_t result = mdbx_limits_keysize_max(pagesize, flags);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::key_max(intptr_t pagesize, key_mode mode) {
  return key_max(pagesize, MDBX_db_flags_t(mode));
}
 
inline size_t env::limits::key_max(const env &env, MDBX_db_flags_t flags) {
  const intptr_t result = mdbx_env_get_maxkeysize_ex(env, flags);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::key_max(const env &env, key_mode mode) { return key_max(env, MDBX_db_flags_t(mode)); }
 
inline size_t env::limits::value_min(MDBX_db_flags_t flags) noexcept { return (flags & MDBX_INTEGERDUP) ? 4 : 0; }
 
inline size_t env::limits::value_min(value_mode mode) noexcept { return value_min(MDBX_db_flags_t(mode)); }
 
inline size_t env::limits::value_max(intptr_t pagesize, MDBX_db_flags_t flags) {
  const intptr_t result = mdbx_limits_valsize_max(pagesize, flags);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::value_max(intptr_t pagesize, value_mode mode) {
  return value_max(pagesize, MDBX_db_flags_t(mode));
}
 
inline size_t env::limits::value_max(const env &env, MDBX_db_flags_t flags) {
  const intptr_t result = mdbx_env_get_maxvalsize_ex(env, flags);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::value_max(const env &env, value_mode mode) { return value_max(env, MDBX_db_flags_t(mode)); }
 
inline size_t env::limits::pairsize4page_max(intptr_t pagesize, MDBX_db_flags_t flags) {
  const intptr_t result = mdbx_limits_pairsize4page_max(pagesize, flags);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::pairsize4page_max(intptr_t pagesize, value_mode mode) {
  return pairsize4page_max(pagesize, MDBX_db_flags_t(mode));
}
 
inline size_t env::limits::pairsize4page_max(const env &env, MDBX_db_flags_t flags) {
  const intptr_t result = mdbx_env_get_pairsize4page_max(env, flags);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::pairsize4page_max(const env &env, value_mode mode) {
  return pairsize4page_max(env, MDBX_db_flags_t(mode));
}
 
inline size_t env::limits::valsize4page_max(intptr_t pagesize, MDBX_db_flags_t flags) {
  const intptr_t result = mdbx_limits_valsize4page_max(pagesize, flags);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::valsize4page_max(intptr_t pagesize, value_mode mode) {
  return valsize4page_max(pagesize, MDBX_db_flags_t(mode));
}
 
inline size_t env::limits::valsize4page_max(const env &env, MDBX_db_flags_t flags) {
  const intptr_t result = mdbx_env_get_valsize4page_max(env, flags);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::valsize4page_max(const env &env, value_mode mode) {
  return valsize4page_max(env, MDBX_db_flags_t(mode));
}
 
inline size_t env::limits::transaction_size_max(intptr_t pagesize) {
  const intptr_t result = mdbx_limits_txnsize_max(pagesize);
  if (result < 0)
    MDBX_CXX20_UNLIKELY error::throw_exception(MDBX_EINVAL);
  return static_cast<size_t>(result);
}
 
inline size_t env::limits::max_map_handles(void) { return MDBX_MAX_DBI; }
 
inline env::operate_parameters env::get_operation_parameters() const {
  const auto flags = get_flags();
  return operate_parameters(max_maps(), max_readers(), operate_parameters::mode_from_flags(flags),
                            operate_parameters::durability_from_flags(flags),
                            operate_parameters::reclaiming_from_flags(flags),
                            operate_parameters::options_from_flags(flags));
}
 
inline env::mode env::get_mode() const { return operate_parameters::mode_from_flags(get_flags()); }
 
inline env::durability env::get_durability() const {
  return env::operate_parameters::durability_from_flags(get_flags());
}
 
inline env::reclaiming_options env::get_reclaiming() const {
  return env::operate_parameters::reclaiming_from_flags(get_flags());
}
 
inline env::operate_options env::get_options() const {
  return env::operate_parameters::options_from_flags(get_flags());
}
 
inline env::stat env::get_stat() const {
  env::stat r;
  error::success_or_throw(::mdbx_env_stat_ex(handle_, nullptr, &r, sizeof(r)));
  return r;
}
 
inline env::stat env::get_stat(const txn &txn) const {
  env::stat r;
  error::success_or_throw(::mdbx_env_stat_ex(handle_, txn, &r, sizeof(r)));
  return r;
}
 
inline env::info env::get_info() const {
  env::info r;
  error::success_or_throw(::mdbx_env_info_ex(handle_, nullptr, &r, sizeof(r)));
  return r;
}
 
inline env::info env::get_info(const txn &txn) const {
  env::info r;
  error::success_or_throw(::mdbx_env_info_ex(handle_, txn, &r, sizeof(r)));
  return r;
}
 
inline filehandle env::get_filehandle() const {
  filehandle fd;
  error::success_or_throw(::mdbx_env_get_fd(handle_, &fd));
  return fd;
}
 
inline MDBX_env_flags_t env::get_flags() const {
  unsigned bits = 0;
  error::success_or_throw(::mdbx_env_get_flags(handle_, &bits));
  return MDBX_env_flags_t(bits);
}
 
inline unsigned env::max_readers() const {
  unsigned r;
  error::success_or_throw(::mdbx_env_get_maxreaders(handle_, &r));
  return r;
}
 
inline unsigned env::max_maps() const {
  unsigned r;
  error::success_or_throw(::mdbx_env_get_maxdbs(handle_, &r));
  return r;
}
 
inline void *env::get_context() const noexcept { return mdbx_env_get_userctx(handle_); }
 
inline env &env::set_context(void *ptr) {
  error::success_or_throw(::mdbx_env_set_userctx(handle_, ptr));
  return *this;
}
 
inline env &env::set_sync_threshold(size_t bytes) {
  error::success_or_throw(::mdbx_env_set_syncbytes(handle_, bytes));
  return *this;
}
 
inline size_t env::sync_threshold() const {
  size_t bytes;
  error::success_or_throw(::mdbx_env_get_syncbytes(handle_, &bytes));
  return bytes;
}
 
inline env &env::set_sync_period__seconds_16dot16(unsigned seconds_16dot16) {
  error::success_or_throw(::mdbx_env_set_syncperiod(handle_, seconds_16dot16));
  return *this;
}
 
inline unsigned env::sync_period__seconds_16dot16() const {
  unsigned seconds_16dot16;
  error::success_or_throw(::mdbx_env_get_syncperiod(handle_, &seconds_16dot16));
  return seconds_16dot16;
}
 
inline env &env::set_sync_period__seconds_double(double seconds) {
  return set_sync_period__seconds_16dot16(unsigned(seconds * 65536));
}
 
inline double env::sync_period__seconds_double() const { return sync_period__seconds_16dot16() / 65536.0; }
 
#if __cplusplus >= 201103L
inline env &env::set_sync_period(const duration &period) { return set_sync_period__seconds_16dot16(period.count()); }
 
inline duration env::sync_period() const { return duration(sync_period__seconds_16dot16()); }
#endif
 
inline env &env::set_extra_option(enum env::extra_runtime_option option, uint64_t value) {
  error::success_or_throw(::mdbx_env_set_option(handle_, ::MDBX_option_t(option), value));
  return *this;
}
 
inline uint64_t env::extra_option(enum env::extra_runtime_option option) const {
  uint64_t value;
  error::success_or_throw(::mdbx_env_get_option(handle_, ::MDBX_option_t(option), &value));
  return value;
}
 
inline env &env::alter_flags(MDBX_env_flags_t flags, bool on_off) {
  error::success_or_throw(::mdbx_env_set_flags(handle_, flags, on_off));
  return *this;
}
 
inline env &env::set_geometry(const geometry &geo) {
  error::success_or_throw(::mdbx_env_set_geometry(handle_, geo.size_lower, geo.size_now, geo.size_upper,
                                                  geo.growth_step, geo.shrink_threshold, geo.pagesize));
  return *this;
}
 
inline bool env::sync_to_disk(bool force, bool nonblock) {
  const int err = ::mdbx_env_sync_ex(handle_, force, nonblock);
  switch (err) {
  case MDBX_SUCCESS /* flush done */:
  case MDBX_RESULT_TRUE /* no data pending for flush to disk */:
    return true;
  case MDBX_BUSY /* the environment is used by other thread */:
    return false;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline void env::close_map(const map_handle &handle) { error::success_or_throw(::mdbx_dbi_close(*this, handle.dbi)); }
 
MDBX_CXX11_CONSTEXPR
env::reader_info::reader_info(int slot, mdbx_pid_t pid, mdbx_tid_t thread, uint64_t txnid, uint64_t lag, size_t used,
                              size_t retained) noexcept
    : slot(slot), pid(pid), thread(thread), transaction_id(txnid), transaction_lag(lag), bytes_used(used),
      bytes_retained(retained) {}
 
template <typename VISITOR> inline int env::enumerate_readers(VISITOR &visitor) {
  struct reader_visitor_thunk : public exception_thunk {
    VISITOR &visitor_;
    static int cb(void *ctx, int number, int slot, mdbx_pid_t pid, mdbx_tid_t thread, uint64_t txnid, uint64_t lag,
                  size_t used, size_t retained) noexcept {
      reader_visitor_thunk *thunk = static_cast<reader_visitor_thunk *>(ctx);
      assert(thunk->is_clean());
      try {
        const reader_info info(slot, pid, thread, txnid, lag, used, retained);
        return loop_control(thunk->visitor_(info, number));
      } catch (... /* capture any exception to rethrow it over C code */) {
        thunk->capture();
        return loop_control::exit_loop;
      }
    }
    MDBX_CXX11_CONSTEXPR reader_visitor_thunk(VISITOR &visitor) noexcept : visitor_(visitor) {}
  };
  reader_visitor_thunk thunk(visitor);
  const auto rc = ::mdbx_reader_list(*this, thunk.cb, &thunk);
  thunk.rethrow_captured();
  return rc;
}
 
inline unsigned env::check_readers() {
  int dead_count;
  error::throw_on_failure(::mdbx_reader_check(*this, &dead_count));
  assert(dead_count >= 0);
  return static_cast<unsigned>(dead_count);
}
 
inline env &env::set_HandleSlowReaders(MDBX_hsr_func *cb) {
  error::success_or_throw(::mdbx_env_set_hsr(handle_, cb));
  return *this;
}
 
inline MDBX_hsr_func *env::get_HandleSlowReaders() const noexcept { return ::mdbx_env_get_hsr(handle_); }
 
inline txn_managed env::start_read() const {
  ::MDBX_txn *ptr;
  error::success_or_throw(::mdbx_txn_begin(handle_, nullptr, MDBX_TXN_RDONLY, &ptr));
  assert(ptr != nullptr);
  return txn_managed(ptr);
}
 
inline txn_managed env::prepare_read() const {
  ::MDBX_txn *ptr;
  error::success_or_throw(::mdbx_txn_begin(handle_, nullptr, MDBX_TXN_RDONLY_PREPARE, &ptr));
  assert(ptr != nullptr);
  return txn_managed(ptr);
}
 
inline txn_managed env::start_write(bool dont_wait) {
  ::MDBX_txn *ptr;
  error::success_or_throw(
      ::mdbx_txn_begin(handle_, nullptr, dont_wait ? MDBX_TXN_READWRITE | MDBX_TXN_TRY : MDBX_TXN_READWRITE, &ptr));
  assert(ptr != nullptr || dont_wait);
  return txn_managed(ptr);
}
 
inline txn_managed env::start_write(txn &parent) {
  ::MDBX_txn *ptr;
  error::success_or_throw(::mdbx_txn_begin(handle_, parent, MDBX_TXN_READWRITE, &ptr));
  assert(ptr != nullptr);
  return txn_managed(ptr);
}
 
inline txn_managed env::try_start_write() { return start_write(true); }
 
MDBX_CXX11_CONSTEXPR txn::txn(MDBX_txn *ptr) noexcept : handle_(ptr) {}
 
inline txn &txn::operator=(txn &&other) noexcept {
  handle_ = other.handle_;
  other.handle_ = nullptr;
  return *this;
}
 
inline txn::txn(txn &&other) noexcept : handle_(other.handle_) { other.handle_ = nullptr; }
 
inline txn::~txn() noexcept {
#ifndef NDEBUG
  handle_ = reinterpret_cast<MDBX_txn *>(uintptr_t(0xDeadBeef));
#endif
}
 
MDBX_CXX14_CONSTEXPR txn::operator bool() const noexcept { return handle_ != nullptr; }
 
MDBX_CXX14_CONSTEXPR txn::operator const MDBX_txn *() const { return handle_; }
 
MDBX_CXX14_CONSTEXPR txn::operator MDBX_txn *() { return handle_; }
 
MDBX_CXX11_CONSTEXPR bool operator==(const txn &a, const txn &b) noexcept { return a.handle_ == b.handle_; }
 
MDBX_CXX11_CONSTEXPR bool operator!=(const txn &a, const txn &b) noexcept { return a.handle_ != b.handle_; }
 
inline void *txn::get_context() const noexcept { return mdbx_txn_get_userctx(handle_); }
 
inline txn &txn::set_context(void *ptr) {
  error::success_or_throw(::mdbx_txn_set_userctx(handle_, ptr));
  return *this;
}
 
inline bool txn::is_dirty(const void *ptr) const {
  int err = ::mdbx_is_dirty(handle_, ptr);
  switch (err) {
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  case MDBX_RESULT_TRUE:
    return true;
  case MDBX_RESULT_FALSE:
    return false;
  }
}
 
inline env txn::env() const noexcept { return ::mdbx_txn_env(handle_); }
 
inline MDBX_txn_flags_t txn::flags() const {
  const int bits = mdbx_txn_flags(handle_);
  error::throw_on_failure((bits != -1) ? MDBX_SUCCESS : MDBX_BAD_TXN);
  return static_cast<MDBX_txn_flags_t>(bits);
}
 
inline uint64_t txn::id() const {
  const uint64_t txnid = mdbx_txn_id(handle_);
  error::throw_on_failure(txnid ? MDBX_SUCCESS : MDBX_BAD_TXN);
  return txnid;
}
 
inline void txn::reset_reading() { error::success_or_throw(::mdbx_txn_reset(handle_)); }
 
inline void txn::make_broken() { error::success_or_throw(::mdbx_txn_break(handle_)); }
 
inline void txn::renew_reading() { error::success_or_throw(::mdbx_txn_renew(handle_)); }
 
inline txn_managed txn::clone(void *context) const {
  MDBX_txn *ptr = nullptr;
  error::success_or_throw(::mdbx_txn_clone(handle_, &ptr, context));
  assert(ptr != nullptr);
  return txn_managed(ptr);
}
 
inline void txn::clone(txn_managed &txn_for_renew_into_clone, void *context) const {
  error::throw_on_nullptr(txn_for_renew_into_clone.handle_, MDBX_BAD_TXN);
  error::success_or_throw(::mdbx_txn_clone(handle_, &txn_for_renew_into_clone.handle_, context));
  assert(txn_for_renew_into_clone.handle_ != nullptr);
}
 
inline void txn::park_reading(bool autounpark) { error::success_or_throw(::mdbx_txn_park(handle_, autounpark)); }
 
inline bool txn::unpark_reading(bool restart_if_ousted) {
  return error::boolean_or_throw(::mdbx_txn_unpark(handle_, restart_if_ousted));
}
 
inline txn::info txn::get_info(bool scan_reader_lock_table) const {
  txn::info r;
  error::success_or_throw(::mdbx_txn_info(handle_, &r, scan_reader_lock_table));
  return r;
}
 
inline cursor_managed txn::open_cursor(map_handle map) const {
  MDBX_cursor *ptr;
  error::success_or_throw(::mdbx_cursor_open(handle_, map.dbi, &ptr));
  return cursor_managed(ptr);
}
 
inline size_t txn::release_all_cursors(bool unbind) const {
  size_t count;
  error::success_or_throw(::mdbx_txn_release_all_cursors_ex(handle_, unbind, &count));
  return count;
}
 
inline map_handle txn::open_map(const slice &name, const ::mdbx::key_mode key_mode,
                                const ::mdbx::value_mode value_mode) const {
  map_handle map;
  error::success_or_throw(
      ::mdbx_dbi_open2(handle_, name, MDBX_db_flags_t(key_mode) | MDBX_db_flags_t(value_mode), &map.dbi));
  assert(map.dbi != 0);
  return map;
}
 
inline map_handle txn::open_map(const char *name, const ::mdbx::key_mode key_mode,
                                const ::mdbx::value_mode value_mode) const {
  map_handle map;
  error::success_or_throw(
      ::mdbx_dbi_open(handle_, name, MDBX_db_flags_t(key_mode) | MDBX_db_flags_t(value_mode), &map.dbi));
  assert(map.dbi != 0);
  return map;
}
 
inline map_handle txn::open_map_accede(const slice &name) const {
  map_handle map;
  error::success_or_throw(::mdbx_dbi_open2(handle_, name, MDBX_DB_ACCEDE, &map.dbi));
  assert(map.dbi != 0);
  return map;
}
 
inline map_handle txn::open_map_accede(const char *name) const {
  map_handle map;
  error::success_or_throw(::mdbx_dbi_open(handle_, name, MDBX_DB_ACCEDE, &map.dbi));
  assert(map.dbi != 0);
  return map;
}
 
inline map_handle txn::create_map(const slice &name, const ::mdbx::key_mode key_mode,
                                  const ::mdbx::value_mode value_mode) {
  map_handle map;
  error::success_or_throw(
      ::mdbx_dbi_open2(handle_, name, MDBX_CREATE | MDBX_db_flags_t(key_mode) | MDBX_db_flags_t(value_mode), &map.dbi));
  assert(map.dbi != 0);
  return map;
}
 
inline map_handle txn::create_map(const char *name, const ::mdbx::key_mode key_mode,
                                  const ::mdbx::value_mode value_mode) {
  map_handle map;
  error::success_or_throw(
      ::mdbx_dbi_open(handle_, name, MDBX_CREATE | MDBX_db_flags_t(key_mode) | MDBX_db_flags_t(value_mode), &map.dbi));
  assert(map.dbi != 0);
  return map;
}
 
inline void txn::drop_map(map_handle map) { error::success_or_throw(::mdbx_drop(handle_, map.dbi, true)); }
 
inline void txn::clear_map(map_handle map) { error::success_or_throw(::mdbx_drop(handle_, map.dbi, false)); }
 
inline void txn::rename_map(map_handle map, const char *new_name) {
  error::success_or_throw(::mdbx_dbi_rename(handle_, map, new_name));
}
 
inline void txn::rename_map(map_handle map, const slice &new_name) {
  error::success_or_throw(::mdbx_dbi_rename2(handle_, map, new_name));
}
 
inline map_handle txn::open_map(const ::std::string &name, const ::mdbx::key_mode key_mode,
                                const ::mdbx::value_mode value_mode) const {
  return open_map(slice(name), key_mode, value_mode);
}
 
inline map_handle txn::open_map_accede(const ::std::string &name) const { return open_map_accede(slice(name)); }
 
inline map_handle txn::create_map(const ::std::string &name, const ::mdbx::key_mode key_mode,
                                  const ::mdbx::value_mode value_mode) {
  return create_map(slice(name), key_mode, value_mode);
}
 
inline bool txn::drop_map(const ::std::string &name, bool throw_if_absent) {
  return drop_map(slice(name), throw_if_absent);
}
 
inline bool txn::clear_map(const ::std::string &name, bool throw_if_absent) {
  return clear_map(slice(name), throw_if_absent);
}
 
inline void txn::rename_map(map_handle map, const ::std::string &new_name) { return rename_map(map, slice(new_name)); }
 
inline txn::map_stat txn::get_map_stat(map_handle map) const {
  txn::map_stat r;
  error::success_or_throw(::mdbx_dbi_stat(handle_, map.dbi, &r, sizeof(r)));
  return r;
}
 
inline uint32_t txn::get_tree_deepmask(map_handle map) const {
  uint32_t r;
  error::success_or_throw(::mdbx_dbi_dupsort_depthmask(handle_, map.dbi, &r));
  return r;
}
 
inline map_handle::info txn::get_map_flags(map_handle map) const {
  unsigned flags, state;
  error::success_or_throw(::mdbx_dbi_flags_ex(handle_, map.dbi, &flags, &state));
  return map_handle::info(MDBX_db_flags_t(flags), MDBX_dbi_state_t(state));
}
 
inline txn &txn::put_canary(const txn::canary &canary) {
  error::success_or_throw(::mdbx_canary_put(handle_, &canary));
  return *this;
}
 
inline txn::canary txn::get_canary() const {
  txn::canary r;
  error::success_or_throw(::mdbx_canary_get(handle_, &r));
  return r;
}
 
inline uint64_t txn::sequence(map_handle map) const {
  uint64_t result;
  error::success_or_throw(::mdbx_dbi_sequence(handle_, map.dbi, &result, 0));
  return result;
}
 
inline uint64_t txn::sequence(map_handle map, uint64_t increment) {
  uint64_t result;
  error::success_or_throw(::mdbx_dbi_sequence(handle_, map.dbi, &result, increment));
  return result;
}
 
inline int txn::compare_keys(map_handle map, const slice &a, const slice &b) const noexcept {
  return ::mdbx_cmp(handle_, map.dbi, &a, &b);
}
 
inline int txn::compare_values(map_handle map, const slice &a, const slice &b) const noexcept {
  return ::mdbx_dcmp(handle_, map.dbi, &a, &b);
}
 
inline int txn::compare_keys(map_handle map, const pair &a, const pair &b) const noexcept {
  return compare_keys(map, a.key, b.key);
}
 
inline int txn::compare_values(map_handle map, const pair &a, const pair &b) const noexcept {
  return compare_values(map, a.value, b.value);
}
 
inline slice txn::get(map_handle map, const slice &key) const {
  slice result;
  error::success_or_throw(::mdbx_get(handle_, map.dbi, &key, &result));
  return result;
}
 
inline slice txn::get(map_handle map, slice key, size_t &values_count) const {
  slice result;
  error::success_or_throw(::mdbx_get_ex(handle_, map.dbi, &key, &result, &values_count));
  return result;
}
 
inline slice txn::get(map_handle map, const slice &key, const slice &value_at_absence) const {
  slice result;
  const int err = ::mdbx_get(handle_, map.dbi, &key, &result);
  switch (err) {
  case MDBX_SUCCESS:
    return result;
  case MDBX_NOTFOUND:
    return value_at_absence;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline slice txn::get(map_handle map, slice key, size_t &values_count, const slice &value_at_absence) const {
  slice result;
  const int err = ::mdbx_get_ex(handle_, map.dbi, &key, &result, &values_count);
  switch (err) {
  case MDBX_SUCCESS:
    return result;
  case MDBX_NOTFOUND:
    return value_at_absence;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline pair_result txn::get_equal_or_great(map_handle map, const slice &key) const {
  pair result(key, slice());
  bool exact = !error::boolean_or_throw(::mdbx_get_equal_or_great(handle_, map.dbi, &result.key, &result.value));
  return pair_result(result.key, result.value, exact);
}
 
inline pair_result txn::get_equal_or_great(map_handle map, const slice &key, const slice &value_at_absence) const {
  pair result{key, slice()};
  const int err = ::mdbx_get_equal_or_great(handle_, map.dbi, &result.key, &result.value);
  switch (err) {
  case MDBX_SUCCESS:
    return pair_result{result.key, result.value, true};
  case MDBX_RESULT_TRUE:
    return pair_result{result.key, result.value, false};
  case MDBX_NOTFOUND:
    return pair_result{key, value_at_absence, false};
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline MDBX_error_t txn::put(map_handle map, const slice &key, slice *value, MDBX_put_flags_t flags) noexcept {
  return MDBX_error_t(::mdbx_put(handle_, map.dbi, &key, value, flags));
}
 
inline void txn::put(map_handle map, const slice &key, slice value, put_mode mode) {
  error::success_or_throw(put(map, key, &value, MDBX_put_flags_t(mode)));
}
 
inline void txn::insert(map_handle map, const slice &key, slice value) {
  error::success_or_throw(put(map, key, &value /* takes the present value in case MDBX_KEYEXIST */,
                              MDBX_put_flags_t(put_mode::insert_unique)));
}
 
inline value_result txn::try_insert(map_handle map, const slice &key, slice value) {
  const int err = put(map, key, &value /* takes the present value in case MDBX_KEYEXIST */,
                      MDBX_put_flags_t(put_mode::insert_unique));
  switch (err) {
  case MDBX_SUCCESS:
    return value_result{slice(), true};
  case MDBX_KEYEXIST:
    return value_result{value, false};
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline slice txn::insert_reserve(map_handle map, const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  error::success_or_throw(put(map, key, &result /* takes the present value in case MDBX_KEYEXIST */,
                              MDBX_put_flags_t(put_mode::insert_unique) | MDBX_RESERVE));
  return result;
}
 
inline value_result txn::try_insert_reserve(map_handle map, const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  const int err = put(map, key, &result /* takes the present value in case MDBX_KEYEXIST */,
                      MDBX_put_flags_t(put_mode::insert_unique) | MDBX_RESERVE);
  switch (err) {
  case MDBX_SUCCESS:
    return value_result{result, true};
  case MDBX_KEYEXIST:
    return value_result{result, false};
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline void txn::upsert(map_handle map, const slice &key, const slice &value) {
  error::success_or_throw(put(map, key, const_cast<slice *>(&value), MDBX_put_flags_t(put_mode::upsert)));
}
 
inline slice txn::upsert_reserve(map_handle map, const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  error::success_or_throw(put(map, key, &result, MDBX_put_flags_t(put_mode::upsert) | MDBX_RESERVE));
  return result;
}
 
inline void txn::update(map_handle map, const slice &key, const slice &value) {
  error::success_or_throw(put(map, key, const_cast<slice *>(&value), MDBX_put_flags_t(put_mode::update)));
}
 
inline bool txn::try_update(map_handle map, const slice &key, const slice &value) {
  const int err = put(map, key, const_cast<slice *>(&value), MDBX_put_flags_t(put_mode::update));
  switch (err) {
  case MDBX_SUCCESS:
    return true;
  case MDBX_NOTFOUND:
    return false;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline slice txn::update_reserve(map_handle map, const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  error::success_or_throw(put(map, key, &result, MDBX_put_flags_t(put_mode::update) | MDBX_RESERVE));
  return result;
}
 
inline value_result txn::try_update_reserve(map_handle map, const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  const int err = put(map, key, &result, MDBX_put_flags_t(put_mode::update) | MDBX_RESERVE);
  switch (err) {
  case MDBX_SUCCESS:
    return value_result{result, true};
  case MDBX_NOTFOUND:
    return value_result{slice(), false};
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline bool txn::erase(map_handle map, const slice &key) {
  const int err = ::mdbx_del(handle_, map.dbi, &key, nullptr);
  switch (err) {
  case MDBX_SUCCESS:
    return true;
  case MDBX_NOTFOUND:
    return false;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline bool txn::erase(map_handle map, const slice &key, const slice &value) {
  const int err = ::mdbx_del(handle_, map.dbi, &key, &value);
  switch (err) {
  case MDBX_SUCCESS:
    return true;
  case MDBX_NOTFOUND:
    return false;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline void txn::replace(map_handle map, const slice &key, slice old_value, const slice &new_value) {
  error::success_or_throw(::mdbx_replace_ex(handle_, map.dbi, &key, const_cast<slice *>(&new_value), &old_value,
                                            MDBX_CURRENT | MDBX_NOOVERWRITE, nullptr, nullptr));
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY>
txn::extract(map_handle map, const slice &key,
             const typename buffer<ALLOCATOR, CAPACITY_POLICY>::allocator_type &alloc) {
  typename buffer<ALLOCATOR, CAPACITY_POLICY>::data_preserver result(alloc);
  error::success_or_throw(
      ::mdbx_replace_ex(handle_, map.dbi, &key, nullptr, &result.slice_, MDBX_CURRENT, result, &result), result);
  return result;
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY>
txn::replace(map_handle map, const slice &key, const slice &new_value,
             const typename buffer<ALLOCATOR, CAPACITY_POLICY>::allocator_type &alloc) {
  typename buffer<ALLOCATOR, CAPACITY_POLICY>::data_preserver result(alloc);
  error::success_or_throw(::mdbx_replace_ex(handle_, map.dbi, &key, const_cast<slice *>(&new_value), &result.slice_,
                                            MDBX_CURRENT, result, &result),
                          result);
  return result;
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
inline buffer<ALLOCATOR, CAPACITY_POLICY>
txn::replace_reserve(map_handle map, const slice &key, slice &new_value,
                     const typename buffer<ALLOCATOR, CAPACITY_POLICY>::allocator_type &alloc) {
  typename buffer<ALLOCATOR, CAPACITY_POLICY>::data_preserver result(alloc);
  error::success_or_throw(::mdbx_replace_ex(handle_, map.dbi, &key, &new_value, &result.slice_,
                                            MDBX_CURRENT | MDBX_RESERVE, result, &result),
                          result);
  return result;
}
 
inline void txn::append(map_handle map, const slice &key, const slice &value, bool multivalue_order_preserved) {
  error::success_or_throw(::mdbx_put(handle_, map.dbi, const_cast<slice *>(&key), const_cast<slice *>(&value),
                                     multivalue_order_preserved ? (MDBX_APPEND | MDBX_APPENDDUP) : MDBX_APPEND));
}
 
inline size_t txn::put_multiple_samelength(map_handle map, const slice &key, const size_t value_length,
                                           const void *values_array, size_t values_count, put_mode mode,
                                           bool allow_partial) {
  MDBX_val args[2] = {{const_cast<void *>(values_array), value_length}, {nullptr, values_count}};
  const int err = ::mdbx_put(handle_, map.dbi, const_cast<slice *>(&key), args, MDBX_put_flags_t(mode) | MDBX_MULTIPLE);
  switch (err) {
  case MDBX_SUCCESS:
    MDBX_CXX20_LIKELY break;
  case MDBX_KEYEXIST:
    if (allow_partial)
      break;
    mdbx_txn_break(handle_);
    MDBX_CXX17_FALLTHROUGH /* fallthrough */;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
  return args[1].iov_len /* done item count */;
}
 
inline ptrdiff_t txn::estimate(map_handle map, const pair &from, const pair &to) const {
  ptrdiff_t result;
  error::success_or_throw(mdbx_estimate_range(handle_, map.dbi, &from.key, &from.value, &to.key, &to.value, &result));
  return result;
}
 
inline ptrdiff_t txn::estimate(map_handle map, const slice &from, const slice &to) const {
  ptrdiff_t result;
  error::success_or_throw(mdbx_estimate_range(handle_, map.dbi, &from, nullptr, &to, nullptr, &result));
  return result;
}
 
inline ptrdiff_t txn::estimate_from_first(map_handle map, const slice &to) const {
  ptrdiff_t result;
  error::success_or_throw(mdbx_estimate_range(handle_, map.dbi, nullptr, nullptr, &to, nullptr, &result));
  return result;
}
 
inline ptrdiff_t txn::estimate_to_last(map_handle map, const slice &from) const {
  ptrdiff_t result;
  error::success_or_throw(mdbx_estimate_range(handle_, map.dbi, &from, nullptr, nullptr, nullptr, &result));
  return result;
}
 
MDBX_CXX11_CONSTEXPR cursor::cursor(MDBX_cursor *ptr) noexcept : handle_(ptr) {}
 
inline cursor_managed cursor::clone(void *your_context) const {
  cursor_managed clone(your_context);
  error::success_or_throw(::mdbx_cursor_copy(handle_, clone.handle_));
  return clone;
}
 
inline void *cursor::get_context() const noexcept { return mdbx_cursor_get_userctx(handle_); }
 
inline cursor &cursor::set_context(void *ptr) {
  error::success_or_throw(::mdbx_cursor_set_userctx(handle_, ptr));
  return *this;
}
 
inline cursor &cursor::operator=(cursor &&other) noexcept {
  handle_ = other.handle_;
  other.handle_ = nullptr;
  return *this;
}
 
inline cursor::cursor(cursor &&other) noexcept : handle_(other.handle_) { other.handle_ = nullptr; }
 
inline cursor::~cursor() noexcept {
#ifndef NDEBUG
  handle_ = reinterpret_cast<MDBX_cursor *>(uintptr_t(0xDeadBeef));
#endif
}
 
MDBX_CXX14_CONSTEXPR cursor::operator bool() const noexcept { return handle_ != nullptr; }
 
MDBX_CXX14_CONSTEXPR cursor::operator const MDBX_cursor *() const { return handle_; }
 
MDBX_CXX14_CONSTEXPR cursor::operator MDBX_cursor *() { return handle_; }
 
MDBX_CXX11_CONSTEXPR bool operator==(const cursor &a, const cursor &b) noexcept { return a.handle_ == b.handle_; }
 
MDBX_CXX11_CONSTEXPR bool operator!=(const cursor &a, const cursor &b) noexcept { return a.handle_ != b.handle_; }
 
inline int compare_position_nothrow(const cursor &left, const cursor &right, bool ignore_nested = false) noexcept {
  return mdbx_cursor_compare(left.handle_, right.handle_, ignore_nested);
}
 
inline int compare_position(const cursor &left, const cursor &right, bool ignore_nested = false) {
  const auto diff = compare_position_nothrow(left, right, ignore_nested);
  assert(compare_position_nothrow(right, left, ignore_nested) == -diff);
  if (MDBX_LIKELY(int16_t(diff) == diff))
    MDBX_CXX20_LIKELY return int(diff);
  else
    throw_incomparable_cursors();
}
 
inline cursor::move_result::move_result(const cursor &cursor, bool throw_notfound) : pair_result() {
  done = cursor.move(get_current, &this->key, &this->value, throw_notfound);
}
 
inline cursor::move_result::move_result(cursor &cursor, move_operation operation, const slice &key, const slice &value,
                                        bool throw_notfound)
    : pair_result(key, value, false) {
  this->done = cursor.move(operation, &this->key, &this->value, throw_notfound);
}
 
inline bool cursor::move(move_operation operation, MDBX_val *key, MDBX_val *value, bool throw_notfound) const {
  const int err = ::mdbx_cursor_get(handle_, key, value, MDBX_cursor_op(operation));
  switch (err) {
  case MDBX_SUCCESS:
    MDBX_CXX20_LIKELY return true;
  case MDBX_RESULT_TRUE:
    return false;
  case MDBX_NOTFOUND:
    if (!throw_notfound)
      return false;
    MDBX_CXX17_FALLTHROUGH /* fallthrough */;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline cursor::estimate_result::estimate_result(const cursor &cursor, move_operation operation, const slice &key,
                                                const slice &value)
    : pair(key, value), approximate_quantity(PTRDIFF_MIN) {
  approximate_quantity = cursor.estimate(operation, &this->key, &this->value);
}
 
inline ptrdiff_t cursor::estimate(move_operation operation, MDBX_val *key, MDBX_val *value) const {
  ptrdiff_t result;
  error::success_or_throw(::mdbx_estimate_move(*this, key, value, MDBX_cursor_op(operation), &result));
  return result;
}
 
inline ptrdiff_t estimate(const cursor &from, const cursor &to) {
  ptrdiff_t result;
  error::success_or_throw(mdbx_estimate_distance(from, to, &result));
  return result;
}
 
inline cursor::move_result cursor::find(const slice &key, bool throw_notfound) {
  return move(key_exact, key, throw_notfound);
}
 
inline cursor::move_result cursor::lower_bound(const slice &key, bool throw_notfound) {
  return move(key_lowerbound, key, throw_notfound);
}
 
inline cursor::move_result cursor::upper_bound(const slice &key, bool throw_notfound) {
  return move(key_greater_than, key, throw_notfound);
}
 
inline cursor::move_result cursor::find_multivalue(const slice &key, const slice &value, bool throw_notfound) {
  return move(multi_find_pair, key, value, throw_notfound);
}
 
inline cursor::move_result cursor::lower_bound_multivalue(const slice &key, const slice &value, bool throw_notfound) {
  return move(multi_exactkey_lowerboundvalue, key, value, throw_notfound);
}
 
inline cursor::move_result cursor::upper_bound_multivalue(const slice &key, const slice &value, bool throw_notfound) {
  return move(multi_exactkey_value_greater, key, value, throw_notfound);
}
 
inline bool cursor::seek(const slice &key) { return move(seek_key, const_cast<slice *>(&key), nullptr, false); }
 
inline size_t cursor::count_multivalue() const {
  size_t result;
  error::success_or_throw(::mdbx_cursor_count(*this, &result));
  return result;
}
 
inline bool cursor::eof() const { return error::boolean_or_throw(::mdbx_cursor_eof(*this)); }
 
inline bool cursor::on_first() const { return error::boolean_or_throw(::mdbx_cursor_on_first(*this)); }
 
inline bool cursor::on_last() const { return error::boolean_or_throw(::mdbx_cursor_on_last(*this)); }
 
inline bool cursor::on_first_multival() const { return error::boolean_or_throw(::mdbx_cursor_on_first_dup(*this)); }
 
inline bool cursor::on_last_multival() const { return error::boolean_or_throw(::mdbx_cursor_on_last_dup(*this)); }
 
inline cursor::estimate_result cursor::estimate(const slice &key, const slice &value) const {
  return estimate_result(*this, multi_exactkey_lowerboundvalue, key, value);
}
 
inline cursor::estimate_result cursor::estimate(const slice &key) const {
  return estimate_result(*this, key_lowerbound, key);
}
 
inline cursor::estimate_result cursor::estimate(move_operation operation) const {
  return estimate_result(*this, operation);
}
 
inline void cursor::renew(::mdbx::txn &txn) { error::success_or_throw(::mdbx_cursor_renew(txn, handle_)); }
 
inline void cursor::bind(::mdbx::txn &txn, ::mdbx::map_handle map_handle) {
  error::success_or_throw(::mdbx_cursor_bind(txn, handle_, map_handle.dbi));
}
 
inline void cursor::unbind() { error::success_or_throw(::mdbx_cursor_unbind(handle_)); }
 
inline txn cursor::txn() const {
  MDBX_txn *txn = ::mdbx_cursor_txn(handle_);
  return ::mdbx::txn(txn);
}
 
inline map_handle cursor::map() const {
  const MDBX_dbi dbi = ::mdbx_cursor_dbi(handle_);
  if (MDBX_UNLIKELY(dbi > MDBX_MAX_DBI))
    error::throw_exception(MDBX_EINVAL);
  return map_handle(dbi);
}
 
inline MDBX_error_t cursor::put(const slice &key, slice *value, MDBX_put_flags_t flags) noexcept {
  return MDBX_error_t(::mdbx_cursor_put(handle_, &key, value, flags));
}
 
inline void cursor::put(const slice &key, slice value, put_mode mode) {
  error::success_or_throw(put(key, &value, MDBX_put_flags_t(mode)));
}
 
inline void cursor::insert(const slice &key, slice value) {
  error::success_or_throw(
      put(key, &value /* takes the present value in case MDBX_KEYEXIST */, MDBX_put_flags_t(put_mode::insert_unique)));
}
 
inline value_result cursor::try_insert(const slice &key, slice value) {
  const int err =
      put(key, &value /* takes the present value in case MDBX_KEYEXIST */, MDBX_put_flags_t(put_mode::insert_unique));
  switch (err) {
  case MDBX_SUCCESS:
    return value_result{slice(), true};
  case MDBX_KEYEXIST:
    return value_result{value, false};
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline slice cursor::insert_reserve(const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  error::success_or_throw(put(key, &result /* takes the present value in case MDBX_KEYEXIST */,
                              MDBX_put_flags_t(put_mode::insert_unique) | MDBX_RESERVE));
  return result;
}
 
inline value_result cursor::try_insert_reserve(const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  const int err = put(key, &result /* takes the present value in case MDBX_KEYEXIST */,
                      MDBX_put_flags_t(put_mode::insert_unique) | MDBX_RESERVE);
  switch (err) {
  case MDBX_SUCCESS:
    return value_result{result, true};
  case MDBX_KEYEXIST:
    return value_result{result, false};
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline void cursor::upsert(const slice &key, const slice &value) {
  error::success_or_throw(put(key, const_cast<slice *>(&value), MDBX_put_flags_t(put_mode::upsert)));
}
 
inline slice cursor::upsert_reserve(const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  error::success_or_throw(put(key, &result, MDBX_put_flags_t(put_mode::upsert) | MDBX_RESERVE));
  return result;
}
 
inline void cursor::update(const slice &key, const slice &value) {
  error::success_or_throw(put(key, const_cast<slice *>(&value), MDBX_put_flags_t(put_mode::update)));
}
 
inline bool cursor::try_update(const slice &key, const slice &value) {
  const int err = put(key, const_cast<slice *>(&value), MDBX_put_flags_t(put_mode::update));
  switch (err) {
  case MDBX_SUCCESS:
    return true;
  case MDBX_NOTFOUND:
    return false;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline slice cursor::update_reserve(const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  error::success_or_throw(put(key, &result, MDBX_put_flags_t(put_mode::update) | MDBX_RESERVE));
  return result;
}
 
inline value_result cursor::try_update_reserve(const slice &key, size_t value_length) {
  slice result(nullptr, value_length);
  const int err = put(key, &result, MDBX_put_flags_t(put_mode::update) | MDBX_RESERVE);
  switch (err) {
  case MDBX_SUCCESS:
    return value_result{result, true};
  case MDBX_NOTFOUND:
    return value_result{slice(), false};
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline bool cursor::erase(bool whole_multivalue) {
  const int err = ::mdbx_cursor_del(handle_, whole_multivalue ? MDBX_ALLDUPS : MDBX_CURRENT);
  switch (err) {
  case MDBX_SUCCESS:
    MDBX_CXX20_LIKELY return true;
  case MDBX_NOTFOUND:
    return false;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
}
 
inline bool cursor::erase(const slice &key, bool whole_multivalue) {
  bool found = seek(key);
  return found ? erase(whole_multivalue) : found;
}
 
inline bool cursor::erase(const slice &key, const slice &value) {
  move_result data = find_multivalue(key, value, false);
  return data.done && erase();
}
 
inline size_t cursor::put_multiple_samelength(const slice &key, const size_t value_length, const void *values_array,
                                              size_t values_count, put_mode mode, bool allow_partial) {
  MDBX_val args[2] = {{const_cast<void *>(values_array), value_length}, {nullptr, values_count}};
  const int err = ::mdbx_cursor_put(handle_, const_cast<slice *>(&key), args, MDBX_put_flags_t(mode) | MDBX_MULTIPLE);
  switch (err) {
  case MDBX_SUCCESS:
    MDBX_CXX20_LIKELY break;
  case MDBX_KEYEXIST:
    if (allow_partial)
      break;
    mdbx_txn_break(txn());
    MDBX_CXX17_FALLTHROUGH /* fallthrough */;
  default:
    MDBX_CXX20_UNLIKELY error::throw_exception(err);
  }
  return args[1].iov_len /* done item count */;
}
 
//------------------------------------------------------------------------------
 
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const slice &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const pair &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const pair_result &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const env::geometry::size &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const env::geometry &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const env::operate_parameters &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const env::mode &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const env::durability &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const env::reclaiming_options &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const env::operate_options &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const env_managed::create_parameters &);
 
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const MDBX_log_level_t &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const MDBX_debug_flags_t &);
LIBMDBX_API ::std::ostream &operator<<(::std::ostream &, const error &);
 
inline ::std::ostream &operator<<(::std::ostream &out, const MDBX_error_t &errcode) { return out << error(errcode); }

 
} // namespace mdbx
 
//------------------------------------------------------------------------------

namespace std {
 
inline string to_string(const ::mdbx::slice &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
template <class ALLOCATOR, typename CAPACITY_POLICY>
inline string to_string(const ::mdbx::buffer<ALLOCATOR, CAPACITY_POLICY> &buffer) {
  ostringstream out;
  out << buffer;
  return out.str();
}
 
inline string to_string(const ::mdbx::pair &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::mdbx::env::geometry &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::mdbx::env::operate_parameters &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::mdbx::env::mode &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::mdbx::env::durability &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::mdbx::env::reclaiming_options &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::mdbx::env::operate_options &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::mdbx::env_managed::create_parameters &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::MDBX_log_level_t &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::MDBX_debug_flags_t &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::mdbx::error &value) {
  ostringstream out;
  out << value;
  return out.str();
}
 
inline string to_string(const ::MDBX_error_t &errcode) { return to_string(::mdbx::error(errcode)); }
 
template <> struct hash<::mdbx::slice> {
  MDBX_CXX14_CONSTEXPR size_t operator()(const ::mdbx::slice &slice) const noexcept { return slice.hash_value(); }
};
 
template <> struct hash<::mdbx::map_handle> {
  MDBX_CXX11_CONSTEXPR size_t operator()(const ::mdbx::map_handle &handle) const noexcept { return handle.dbi; }
};
 
template <> struct hash<::mdbx::env> : public std::hash<const MDBX_env *> {
  using inherited = std::hash<const MDBX_env *>;
  size_t operator()(const ::mdbx::env &env) const noexcept { return inherited::operator()(env); }
};
 
template <> struct hash<::mdbx::txn> : public std::hash<const MDBX_txn *> {
  using inherited = std::hash<const MDBX_txn *>;
  size_t operator()(const ::mdbx::txn &txn) const noexcept { return inherited::operator()(txn); }
};
 
template <> struct hash<::mdbx::cursor> : public std::hash<const MDBX_cursor *> {
  using inherited = std::hash<const MDBX_cursor *>;
  size_t operator()(const ::mdbx::cursor &cursor) const noexcept { return inherited::operator()(cursor); }
};
 
template <class ALLOCATOR, typename CAPACITY_POLICY> struct hash<::mdbx::buffer<ALLOCATOR, CAPACITY_POLICY>> {
  size_t operator()(::mdbx::buffer<ALLOCATOR, CAPACITY_POLICY> const &buffer) const noexcept {
    return buffer.hash_value();
  }
};
 
} // namespace std
 
#if defined(__LCC__) && __LCC__ >= 126
#pragma diagnostic pop
#endif
 
#ifdef _MSC_VER
#pragma warning(pop)
#endif