libcxx/include/__memory/construct_at.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___MEMORY_CONSTRUCT_AT_H
#define _LIBCPP___MEMORY_CONSTRUCT_AT_H

#include <__assert>
#include <__config>
#include <__iterator/access.h>
#include <__memory/addressof.h>
#include <__new/placement_new_delete.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/is_array.h>
#include <__utility/declval.h>
#include <__utility/forward.h>
#include <__utility/move.h>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

// construct_at

#if _LIBCPP_STD_VER >= 20

template <class _Tp, class... _Args, class = decltype(::new(std::declval<void*>()) _Tp(std::declval<_Args>()...))>
_LIBCPP_HIDE_FROM_ABI constexpr _Tp* construct_at(_Tp* __location, _Args&&... __args) {
  _LIBCPP_ASSERT_NON_NULL(__location != nullptr, "null pointer given to construct_at");
  return ::new (static_cast<void*>(__location)) _Tp(std::forward<_Args>(__args)...);
}

#endif

template <class _Tp, class... _Args, class = decltype(::new(std::declval<void*>()) _Tp(std::declval<_Args>()...))>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp* __construct_at(_Tp* __location, _Args&&... __args) {
#if _LIBCPP_STD_VER >= 20
  return std::construct_at(__location, std::forward<_Args>(__args)...);
#else
  return _LIBCPP_ASSERT_NON_NULL(__location != nullptr, "null pointer given to construct_at"),
         ::new (static_cast<void*>(__location)) _Tp(std::forward<_Args>(__args)...);
#endif
}

// destroy_at

// The internal functions are available regardless of the language version (with the exception of the `__destroy_at`
// taking an array).

template <class _Tp, __enable_if_t<!is_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __destroy_at(_Tp* __loc) {
  _LIBCPP_ASSERT_NON_NULL(__loc != nullptr, "null pointer given to destroy_at");
  __loc->~_Tp();
}

#if _LIBCPP_STD_VER >= 20
template <class _Tp, __enable_if_t<is_array<_Tp>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __destroy_at(_Tp* __loc) {
  _LIBCPP_ASSERT_NON_NULL(__loc != nullptr, "null pointer given to destroy_at");
  auto const __end = std::end(*__loc);
  for (auto __it = std::begin(*__loc); __it != __end; ++__it)
    std::__destroy_at(__it);
}
#endif

#if _LIBCPP_STD_VER >= 17

template <class _Tp, enable_if_t<!is_array_v<_Tp>, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void destroy_at(_Tp* __loc) {
  std::__destroy_at(__loc);
}

#  if _LIBCPP_STD_VER >= 20
template <class _Tp, enable_if_t<is_array_v<_Tp>, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void destroy_at(_Tp* __loc) {
  std::__destroy_at(__loc);
}
#  endif

#endif // _LIBCPP_STD_VER >= 17

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___MEMORY_CONSTRUCT_AT_H