gcc/libstdc++-v3/include/ext/type_traits.h

// -*- C++ -*-

// Copyright (C) 2005-2022 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library 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, or (at your option) any later
// version.

// This library 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.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file ext/type_traits.h
 *  This file is a GNU extension to the Standard C++ Library.
 */

#ifndef _EXT_TYPE_TRAITS
#define _EXT_TYPE_TRAITS 1

#pragma GCC system_header

#include <bits/c++config.h>
#include <bits/cpp_type_traits.h>

extern "C++" {

namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  // Define a nested type if some predicate holds.
  template<bool, typename>
    struct __enable_if 
    { };

  template<typename _Tp>
    struct __enable_if<true, _Tp>
    { typedef _Tp __type; };


  // Conditional expression for types. If true, first, if false, second.
  template<bool _Cond, typename _Iftrue, typename _Iffalse>
    struct __conditional_type
    { typedef _Iftrue __type; };

  template<typename _Iftrue, typename _Iffalse>
    struct __conditional_type<false, _Iftrue, _Iffalse>
    { typedef _Iffalse __type; };


  // Given an integral builtin type, return the corresponding unsigned type.
  template<typename _Tp>
    struct __add_unsigned
    { 
    private:
      typedef __enable_if<std::__is_integer<_Tp>::__value, _Tp> __if_type;
      
    public:
      typedef typename __if_type::__type __type; 
    };

  template<>
    struct __add_unsigned<char>
    { typedef unsigned char __type; };

  template<>
    struct __add_unsigned<signed char>
    { typedef unsigned char __type; };

  template<>
    struct __add_unsigned<short>
    { typedef unsigned short __type; };

  template<>
    struct __add_unsigned<int>
    { typedef unsigned int __type; };

  template<>
    struct __add_unsigned<long>
    { typedef unsigned long __type; };

  template<>
    struct __add_unsigned<long long>
    { typedef unsigned long long __type; };

  // Declare but don't define.
  template<>
    struct __add_unsigned<bool>;

  template<>
    struct __add_unsigned<wchar_t>;


  // Given an integral builtin type, return the corresponding signed type.
  template<typename _Tp>
    struct __remove_unsigned
    { 
    private:
      typedef __enable_if<std::__is_integer<_Tp>::__value, _Tp> __if_type;
      
    public:
      typedef typename __if_type::__type __type; 
    };

  template<>
    struct __remove_unsigned<char>
    { typedef signed char __type; };

  template<>
    struct __remove_unsigned<unsigned char>
    { typedef signed char __type; };

  template<>
    struct __remove_unsigned<unsigned short>
    { typedef short __type; };

  template<>
    struct __remove_unsigned<unsigned int>
    { typedef int __type; };

  template<>
    struct __remove_unsigned<unsigned long>
    { typedef long __type; };

  template<>
    struct __remove_unsigned<unsigned long long>
    { typedef long long __type; };

  // Declare but don't define.
  template<>
    struct __remove_unsigned<bool>;

  template<>
    struct __remove_unsigned<wchar_t>;


  // For use in string and vstring.
  template<typename _Type>
    _GLIBCXX_CONSTEXPR
    inline bool
    __is_null_pointer(_Type* __ptr)
    { return __ptr == 0; }

  template<typename _Type>
    _GLIBCXX_CONSTEXPR
    inline bool
    __is_null_pointer(_Type)
    { return false; }

#if __cplusplus >= 201103L
  constexpr bool
  __is_null_pointer(std::nullptr_t)
  { return true; }
#endif

  // For arithmetic promotions in <complex> and <cmath>

  template<typename _Tp, bool = std::__is_integer<_Tp>::__value>
    struct __promote
    { typedef double __type; };

  // No nested __type member for non-integer non-floating point types,
  // allows this type to be used for SFINAE to constrain overloads in
  // <cmath> and <complex> to only the intended types.
  template<typename _Tp>
    struct __promote<_Tp, false>
    { };

  template<>
    struct __promote<long double>
    { typedef long double __type; };

  template<>
    struct __promote<double>
    { typedef double __type; };

  template<>
    struct __promote<float>
    { typedef float __type; };

#if __cpp_fold_expressions

  template<typename... _Tp>
    using __promoted_t = decltype((typename __promote<_Tp>::__type(0) + ...));

  // Deducing the promoted type is done by __promoted_t<_Tp...>,
  // then __promote is used to provide the nested __type member.
  template<typename _Tp, typename _Up>
    using __promote_2 = __promote<__promoted_t<_Tp, _Up>>;

  template<typename _Tp, typename _Up, typename _Vp>
    using __promote_3 = __promote<__promoted_t<_Tp, _Up, _Vp>>;

  template<typename _Tp, typename _Up, typename _Vp, typename _Wp>
    using __promote_4 = __promote<__promoted_t<_Tp, _Up, _Vp, _Wp>>;

#else

  template<typename _Tp, typename _Up,
           typename _Tp2 = typename __promote<_Tp>::__type,
           typename _Up2 = typename __promote<_Up>::__type>
    struct __promote_2
    {
      typedef __typeof__(_Tp2() + _Up2()) __type;
    };

  template<typename _Tp, typename _Up, typename _Vp,
           typename _Tp2 = typename __promote<_Tp>::__type,
           typename _Up2 = typename __promote<_Up>::__type,
           typename _Vp2 = typename __promote<_Vp>::__type>
    struct __promote_3
    {
      typedef __typeof__(_Tp2() + _Up2() + _Vp2()) __type;
    };

  template<typename _Tp, typename _Up, typename _Vp, typename _Wp,
           typename _Tp2 = typename __promote<_Tp>::__type,
           typename _Up2 = typename __promote<_Up>::__type,
           typename _Vp2 = typename __promote<_Vp>::__type,
           typename _Wp2 = typename __promote<_Wp>::__type>
    struct __promote_4
    {
      typedef __typeof__(_Tp2() + _Up2() + _Vp2() + _Wp2()) __type;
    };
#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
} // extern "C++"

#endif