uses_allocator_args.h

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// Utility functions for uses-allocator construction -*- C++ -*-
 
// Copyright (C) 2019-2025 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 include/bits/uses_allocator_args.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{memory}
 */
 
#ifndef _USES_ALLOCATOR_ARGS
#define _USES_ALLOCATOR_ARGS 1
 
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
 
#include <bits/version.h>
 
#ifdef __glibcxx_make_obj_using_allocator // C++ >= 20 && concepts
#include <new>                       // for placement operator new
#include <tuple>           // for tuple, make_tuple, make_from_tuple
#include <bits/stl_construct.h> // construct_at
#include <bits/stl_pair.h>      // pair
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
  template<typename _Tp>
    concept _Std_pair = __is_pair<remove_cv_t<_Tp>>;
 
/** @addtogroup allocators
 *  @{
 */
  template<typename _Tp, typename _Alloc, typename... _Args>
    constexpr auto
    uses_allocator_construction_args(const _Alloc& __a,
                                     _Args&&... __args) noexcept
    requires (! _Std_pair<_Tp>)
    {
      if constexpr (uses_allocator_v<remove_cv_t<_Tp>, _Alloc>)
        {
          if constexpr (is_constructible_v<_Tp, allocator_arg_t,
                                           const _Alloc&, _Args...>)
            {
              return tuple<allocator_arg_t, const _Alloc&, _Args&&...>(
                  allocator_arg, __a, std::forward<_Args>(__args)...);
            }
          else
            {
              static_assert(is_constructible_v<_Tp, _Args..., const _Alloc&>,
                  "construction with an allocator must be possible"
                  " if uses_allocator is true");
 
              return tuple<_Args&&..., const _Alloc&>(
                  std::forward<_Args>(__args)..., __a);
            }
        }
      else
        {
          static_assert(is_constructible_v<_Tp, _Args...>);
 
          return tuple<_Args&&...>(std::forward<_Args>(__args)...);
        }
    }
 
  template<_Std_pair _Tp, typename _Alloc, typename _Tuple1, typename _Tuple2>
    constexpr auto
    uses_allocator_construction_args(const _Alloc& __a, piecewise_construct_t,
                                     _Tuple1&& __x, _Tuple2&& __y) noexcept;
 
  template<_Std_pair _Tp, typename _Alloc>
    constexpr auto
    uses_allocator_construction_args(const _Alloc&) noexcept;
 
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc&, _Up&&, _Vp&&) noexcept;
 
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc&,
                                     const pair<_Up, _Vp>&) noexcept;
 
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc&, pair<_Up, _Vp>&&) noexcept;
 
#if __cplusplus > 202002L
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc&,
                                     pair<_Up, _Vp>&) noexcept;
 
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc&, const pair<_Up, _Vp>&&) noexcept;
#endif // C++23
 
  template<_Std_pair _Tp, typename _Alloc, typename _Tuple1, typename _Tuple2>
    constexpr auto
    uses_allocator_construction_args(const _Alloc& __a, piecewise_construct_t,
                                     _Tuple1&& __x, _Tuple2&& __y) noexcept
    {
      using _Tp1 = typename _Tp::first_type;
      using _Tp2 = typename _Tp::second_type;
 
      return std::make_tuple(piecewise_construct,
          std::apply([&__a](auto&&... __args1) {
              return std::uses_allocator_construction_args<_Tp1>(
                  __a, std::forward<decltype(__args1)>(__args1)...);
          }, std::forward<_Tuple1>(__x)),
          std::apply([&__a](auto&&... __args2) {
              return std::uses_allocator_construction_args<_Tp2>(
                  __a, std::forward<decltype(__args2)>(__args2)...);
          }, std::forward<_Tuple2>(__y)));
    }
 
  template<_Std_pair _Tp, typename _Alloc>
    constexpr auto
    uses_allocator_construction_args(const _Alloc& __a) noexcept
    {
      using _Tp1 = typename _Tp::first_type;
      using _Tp2 = typename _Tp::second_type;
 
      return std::make_tuple(piecewise_construct,
          std::uses_allocator_construction_args<_Tp1>(__a),
          std::uses_allocator_construction_args<_Tp2>(__a));
    }
 
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc& __a, _Up&& __u, _Vp&& __v)
      noexcept
    {
      using _Tp1 = typename _Tp::first_type;
      using _Tp2 = typename _Tp::second_type;
 
      return std::make_tuple(piecewise_construct,
          std::uses_allocator_construction_args<_Tp1>(__a,
            std::forward<_Up>(__u)),
          std::uses_allocator_construction_args<_Tp2>(__a,
            std::forward<_Vp>(__v)));
    }
 
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc& __a,
                                     const pair<_Up, _Vp>& __pr) noexcept
    {
      using _Tp1 = typename _Tp::first_type;
      using _Tp2 = typename _Tp::second_type;
 
      return std::make_tuple(piecewise_construct,
          std::uses_allocator_construction_args<_Tp1>(__a, __pr.first),
          std::uses_allocator_construction_args<_Tp2>(__a, __pr.second));
    }
 
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc& __a,
                                     pair<_Up, _Vp>&& __pr) noexcept
    {
      using _Tp1 = typename _Tp::first_type;
      using _Tp2 = typename _Tp::second_type;
 
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 3527. uses_allocator_construction_args handles rvalue pairs
      // of rvalue references incorrectly
      return std::make_tuple(piecewise_construct,
          std::uses_allocator_construction_args<_Tp1>(__a,
            std::get<0>(std::move(__pr))),
          std::uses_allocator_construction_args<_Tp2>(__a,
            std::get<1>(std::move(__pr))));
    }
 
#if __cplusplus > 202002L
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc& __a,
                                     pair<_Up, _Vp>& __pr) noexcept
    {
      using _Tp1 = typename _Tp::first_type;
      using _Tp2 = typename _Tp::second_type;
 
      return std::make_tuple(piecewise_construct,
          std::uses_allocator_construction_args<_Tp1>(__a, __pr.first),
          std::uses_allocator_construction_args<_Tp2>(__a, __pr.second));
    }
 
  template<_Std_pair _Tp, typename _Alloc, typename _Up, typename _Vp>
    constexpr auto
    uses_allocator_construction_args(const _Alloc& __a,
                                     const pair<_Up, _Vp>&& __pr) noexcept
    {
      using _Tp1 = typename _Tp::first_type;
      using _Tp2 = typename _Tp::second_type;
 
      return std::make_tuple(piecewise_construct,
          std::uses_allocator_construction_args<_Tp1>(__a,
            std::get<0>(std::move(__pr))),
          std::uses_allocator_construction_args<_Tp2>(__a,
            std::get<1>(std::move(__pr))));
    }
#endif // C++23
 
  template<typename _Tp, typename _Alloc, typename... _Args>
    constexpr _Tp
    make_obj_using_allocator(const _Alloc& __a, _Args&&... __args)
    {
      return std::make_from_tuple<_Tp>(
          std::uses_allocator_construction_args<_Tp>(__a,
            std::forward<_Args>(__args)...));
    }
 
  template<typename _Tp, typename _Alloc, typename... _Args>
    constexpr _Tp*
    uninitialized_construct_using_allocator(_Tp* __p, const _Alloc& __a,
                                            _Args&&... __args)
    {
      return std::apply([&](auto&&... __xs) {
        return std::construct_at(__p, std::forward<decltype(__xs)>(__xs)...);
      }, std::uses_allocator_construction_args<_Tp>(__a,
        std::forward<_Args>(__args)...));
    }
/// @}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // __glibcxx_make_obj_using_allocator
#endif // _USES_ALLOCATOR_ARGS