libstdc++-v3/include/bits/uses_allocator.h

// Uses-allocator Construction -*- C++ -*-

// Copyright (C) 2010-2026 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_H
#define _USES_ALLOCATOR_H 1

#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else

#include <type_traits>
#include <bits/move.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/// @cond undocumented

  // This is used for std::experimental::erased_type from Library Fundamentals.
  struct __erased_type { };

  // This also supports the "type-erased allocator" protocol from the
  // Library Fundamentals TS, where allocator_type is erased_type.
  // The second condition will always be false for types not using the TS.
  template<typename _Alloc, typename _Tp>
    using __is_erased_or_convertible
      = __or_<is_convertible<_Alloc, _Tp>, is_same<_Tp, __erased_type>>;

  /// [allocator.tag]
  struct allocator_arg_t { explicit allocator_arg_t() = default; };

  _GLIBCXX17_INLINE constexpr allocator_arg_t allocator_arg =
    allocator_arg_t();

  template<typename _Tp, typename _Alloc, typename = __void_t<>>
    struct __uses_allocator_helper
    : false_type { };

  template<typename _Tp, typename _Alloc>
    struct __uses_allocator_helper<_Tp, _Alloc,
				   __void_t<typename _Tp::allocator_type>>
    : __is_erased_or_convertible<_Alloc, typename _Tp::allocator_type>::type
    { };

  /// [allocator.uses.trait]
  template<typename _Tp, typename _Alloc>
    struct uses_allocator
    : __uses_allocator_helper<_Tp, _Alloc>::type
    { };

  struct __uses_alloc_base { };

  struct __uses_alloc0 : __uses_alloc_base
  {
    struct _Sink { void _GLIBCXX20_CONSTEXPR operator=(const void*) { } } _M_a;
  };

  template<typename _Alloc>
    struct __uses_alloc1 : __uses_alloc_base { const _Alloc* _M_a; };

  template<typename _Alloc>
    struct __uses_alloc2 : __uses_alloc_base { const _Alloc* _M_a; };

  template<bool, typename _Tp, typename _Alloc, typename... _Args>
    struct __uses_alloc;

  template<typename _Tp, typename _Alloc, typename... _Args>
    struct __uses_alloc<true, _Tp, _Alloc, _Args...>
    : __conditional_t<
        is_constructible<_Tp, allocator_arg_t, const _Alloc&, _Args...>::value,
        __uses_alloc1<_Alloc>,
       	__uses_alloc2<_Alloc>>
    {
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2586. Wrong value category used in scoped_allocator_adaptor::construct
      static_assert(__or_<
	  is_constructible<_Tp, allocator_arg_t, const _Alloc&, _Args...>,
	  is_constructible<_Tp, _Args..., const _Alloc&>>::value,
	  "construction with an allocator must be possible"
	  " if uses_allocator is true");
    };

  template<typename _Tp, typename _Alloc, typename... _Args>
    struct __uses_alloc<false, _Tp, _Alloc, _Args...>
    : __uses_alloc0 { };

  template<typename _Tp, typename _Alloc, typename... _Args>
    using __uses_alloc_t =
      __uses_alloc<uses_allocator<_Tp, _Alloc>::value, _Tp, _Alloc, _Args...>;

  template<typename _Tp, typename _Alloc, typename... _Args>
    _GLIBCXX20_CONSTEXPR
    inline __uses_alloc_t<_Tp, _Alloc, _Args...>
    __use_alloc(const _Alloc& __a)
    {
      __uses_alloc_t<_Tp, _Alloc, _Args...> __ret;
      __ret._M_a = std::__addressof(__a);
      return __ret;
    }

  template<typename _Tp, typename _Alloc, typename... _Args>
    void
    __use_alloc(const _Alloc&&) = delete;

#if __cplusplus > 201402L
  template <typename _Tp, typename _Alloc>
    inline constexpr bool uses_allocator_v =
      uses_allocator<_Tp, _Alloc>::value;
#endif // C++17

#if __cpp_concepts
  template<typename _Alloc, typename... _Ts>
    concept __allocator_for = (uses_allocator_v<_Ts, _Alloc> && ...);
#endif

  template<template<typename...> class _Predicate,
	   typename _Tp, typename _Alloc, typename... _Args>
    struct __is_uses_allocator_predicate
    : __conditional_t<uses_allocator<_Tp, _Alloc>::value,
      __or_<_Predicate<_Tp, allocator_arg_t, _Alloc, _Args...>,
	    _Predicate<_Tp, _Args..., _Alloc>>,
      _Predicate<_Tp, _Args...>> { };

  template<typename _Tp, typename _Alloc, typename... _Args>
    struct __is_uses_allocator_constructible
    : __is_uses_allocator_predicate<is_constructible, _Tp, _Alloc, _Args...>
    { };

#if __cplusplus >= 201402L
  template<typename _Tp, typename _Alloc, typename... _Args>
    _GLIBCXX17_INLINE constexpr bool __is_uses_allocator_constructible_v =
      __is_uses_allocator_constructible<_Tp, _Alloc, _Args...>::value;
#endif // C++14

  template<typename _Tp, typename _Alloc, typename... _Args>
    struct __is_nothrow_uses_allocator_constructible
    : __is_uses_allocator_predicate<is_nothrow_constructible,
				    _Tp, _Alloc, _Args...>
    { };


#if __cplusplus >= 201402L
  template<typename _Tp, typename _Alloc, typename... _Args>
    _GLIBCXX17_INLINE constexpr bool
    __is_nothrow_uses_allocator_constructible_v =
      __is_nothrow_uses_allocator_constructible<_Tp, _Alloc, _Args...>::value;
#endif // C++14

  template<typename _Tp, typename... _Args>
    void __uses_allocator_construct_impl(__uses_alloc0, _Tp* __ptr,
					 _Args&&... __args)
    { ::new ((void*)__ptr) _Tp(std::forward<_Args>(__args)...); }

  template<typename _Tp, typename _Alloc, typename... _Args>
    void __uses_allocator_construct_impl(__uses_alloc1<_Alloc> __a, _Tp* __ptr,
					 _Args&&... __args)
    {
      ::new ((void*)__ptr) _Tp(allocator_arg, *__a._M_a,
			       std::forward<_Args>(__args)...);
    }

  template<typename _Tp, typename _Alloc, typename... _Args>
    void __uses_allocator_construct_impl(__uses_alloc2<_Alloc> __a, _Tp* __ptr,
					 _Args&&... __args)
    { ::new ((void*)__ptr) _Tp(std::forward<_Args>(__args)..., *__a._M_a); }

  template<typename _Tp, typename _Alloc, typename... _Args>
    void __uses_allocator_construct(const _Alloc& __a, _Tp* __ptr,
				    _Args&&... __args)
    {
      std::__uses_allocator_construct_impl(
	  std::__use_alloc<_Tp, _Alloc, _Args...>(__a), __ptr,
	  std::forward<_Args>(__args)...);
    }

/// @endcond
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif
#endif