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 <__memory/addressof.h>
#include <__new/placement_new_delete.h>
#include <__type_traits/is_array.h>
#include <__utility/declval.h>
#include <__utility/forward.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* _LIBCPP_DIAGNOSE_NULLPTR __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>
_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");
#if _LIBCPP_STD_VER >= 20
  if constexpr (is_array_v<_Tp>) {
    for (auto&& __val : *__loc)
      std::__destroy_at(std::addressof(__val));
  } else
#endif
  {
    __loc->~_Tp();
  }
}

#if _LIBCPP_STD_VER >= 17
template <class _Tp>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void destroy_at(_Tp* _LIBCPP_DIAGNOSE_NULLPTR __loc) {
  std::__destroy_at(__loc);
}
#endif // _LIBCPP_STD_VER >= 17

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___MEMORY_CONSTRUCT_AT_H