tdecl.h

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/* *****************************************************************************
 * kblib is a general utility library for C++14 and C++17, intended to provide
 * performant high-level abstractions and more expressive ways to do simple
 * things.
 *
 * Copyright (c) 2021 killerbee
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 * ****************************************************************************/
 
#ifndef KBLIB_TDECL_H
#define KBLIB_TDECL_H
 
#include <cstddef>
#if __has_include(<version>)
#  include <version>
#endif
 
#if __cplusplus < 201402L
#  error kblib requires C++14 or higher
#endif
 
#define KBLIB_X(X) X
 
#define KBLIB_VERS_MAJ 00
#define KBLIB_VERS_MIN 04
#define KBLIB_VERS_REV 02
#define KBLIB_VERS_I(P, MAJ, MIN, REV) KBLIB_VERS_I2(P, MAJ, MIN, REV)
#define KBLIB_VERS_I2(P, MAJ, MIN, REV) P##MAJ##MIN##REV
 
// VMMmmrr
#define KBLIB_VERS_S \
   KBLIB_VERS_I(KBV, KBLIB_VERS_MAJ, KBLIB_VERS_MIN, KBLIB_VERS_REV)
// 1MMmmrr
#define KBLIB_VERS \
   KBLIB_VERS_I(1, KBLIB_VERS_MAJ, KBLIB_VERS_MIN, KBLIB_VERS_REV)
 
#if (__cplusplus >= 201703L)
#  define KBLIB_USE_CXX17 1
#else
#  define KBLIB_USE_CXX17 0
#endif
 
#if (__cplusplus >= 202002L)
#  define KBLIB_USE_CXX20 1
#else
#  define KBLIB_USE_CXX20 0
#endif
#ifndef KBLIB_USE_STRING_VIEW
#  if KBLIB_USE_CXX17
#     define KBLIB_USE_STRING_VIEW 1
#  else
#     define KBLIB_USE_STRING_VIEW 0
#  endif
#endif
 
#ifndef KBLIB_USE_SPANSTREAM
#  if __cpp_lib_spanstream
#     define KBLIB_USE_SPANSTREAM 1
#  else
#     define KBLIB_USE_SPANSTREAM 0
#  endif
#endif
 
#if KBLIB_USE_CXX20
#  define KBLIB_CXX20(args) args
#else
#  define KBLIB_CXX20(args)
#endif
 
// used to prevent cross-linkage between incompatible library versions
#define KBLIB_VERS_NS_I(VS, CXX17, CXX_SV, CXX_SS, CXX20) \
   KBLIB_VERS_NS_I2(VS, CXX17, CXX_SV, CXX_SS, CXX20)
#define KBLIB_VERS_NS_I2(VS, CXX17, CXX_SV, CXX_SS, CXX20) \
   VS##_##CXX17##CXX_SV##CXX_SS##CXX20
 
#define KBLIB_VERS_NS                                                    \
   KBLIB_VERS_NS_I(KBLIB_VERS_S, KBLIB_USE_CXX17, KBLIB_USE_STRING_VIEW, \
                   KBLIB_USE_SPANSTREAM, KBLIB_USE_CXX20)
 
#ifndef _DOXYGEN_
#  define KBLIB_NS KBLIB_VERS_NS
namespace KBLIB_NS {}
namespace kblib = KBLIB_NS;
#else
#  define KBLIB_NS kblib
#endif
 
// Note that __has_cpp_attribute(nodiscard) does not work with at least certain
// versions of Clang
#if KBLIB_USE_CXX17
#  define KBLIB_NODISCARD [[nodiscard]]
#  define KBLIB_UNUSED [[maybe_unused]]
#else
#  define KBLIB_NODISCARD [[gnu::warn_unused_result]]
#  define KBLIB_UNUSED [[gnu::unused]]
#endif
 
#if KBLIB_USE_CXX17
#  define KBLIB_CONSTANT constexpr inline
#  define KBLIB_CONSTANT_V constexpr inline bool
#  define KBLIB_CONSTANT_M constexpr inline static
#  define KBLIB_CONSTANT_MV constexpr inline static bool
#else
#  define KBLIB_CONSTANT constexpr
#  define KBLIB_CONSTANT_V constexpr bool
#  define KBLIB_CONSTANT_M constexpr static
#  define KBLIB_CONSTANT_MV constexpr static bool
#endif
 
#if defined(_DOXYGEN_) and not defined(KBLIB_DEF_MACROS)
#  define KBLIB_DEF_MACROS
#endif
 
namespace KBLIB_NS {
 
namespace detail {
 
   template <typename Container, bool, typename...>
   struct buildiota_impl;
 
   template <typename T>
   struct tag {
      using type = T;
   };
 
   template <typename T>
   struct no_dangle {
      using type = T&;
   };
 
   template <typename T>
   struct no_dangle<T&&> {
      using type = T;
   };
 
   template <typename T>
   using no_dangle_t = typename no_dangle<T>::type;
 
} // namespace detail
enum class endian { unknown, little, big, weird };
 
#ifdef __BYTE_ORDER__
namespace detail {
   KBLIB_NODISCARD constexpr auto get_system_endian() -> endian {
      if (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__) {
         return endian::big;
      } else if (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__) {
         return endian::little;
      } else {
         return endian::weird;
      }
   }
} // namespace detail
 
constexpr endian system_endian = detail::get_system_endian();
#else
constexpr endian system_endian = endian::unknown;
#endif
 
namespace detail {
   KBLIB_NODISCARD constexpr auto get_hash_order() -> endian {
      if (system_endian == endian::little or system_endian == endian::big) {
         return system_endian;
      } else {
         return endian::little;
      }
   }
} // namespace detail
 
#ifdef KBLIB_CONSISTENT_HASHES
constexpr endian hash_order = little;
#else
constexpr endian hash_order = detail::get_hash_order();
#endif
 
#if KBLIB_USE_CXX17
using std::byte;
#else
using byte = unsigned char;
#endif
 
} // namespace KBLIB_NS
 
#endif // KBLIB_TDECL_H