llvm-project/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 <__memory/voidify.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>
#include <new>

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

_LIBCPP_BEGIN_NAMESPACE_STD

// construct_at

#if _LIBCPP_STD_VER > 17

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(__location != nullptr, "null pointer given to construct_at");
  return ::new (_VSTD::__voidify(*__location)) _Tp(_VSTD::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 _Tp* __construct_at(_Tp* __location, _Args&&... __args) {
#if _LIBCPP_STD_VER > 17
  return std::construct_at(__location, std::forward<_Args>(__args)...);
#else
  return _LIBCPP_ASSERT(__location != nullptr, "null pointer given to construct_at"),
         ::new (std::__voidify(*__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 _ForwardIterator>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
_ForwardIterator __destroy(_ForwardIterator, _ForwardIterator);

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

#if _LIBCPP_STD_VER > 17
template <class _Tp, typename enable_if<is_array<_Tp>::value, int>::type = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
void __destroy_at(_Tp* __loc) {
    _LIBCPP_ASSERT(__loc != nullptr, "null pointer given to destroy_at");
    _VSTD::__destroy(_VSTD::begin(*__loc), _VSTD::end(*__loc));
}
#endif

template <class _ForwardIterator>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
_ForwardIterator __destroy(_ForwardIterator __first, _ForwardIterator __last) {
    for (; __first != __last; ++__first)
        _VSTD::__destroy_at(_VSTD::addressof(*__first));
    return __first;
}

#if _LIBCPP_STD_VER > 14

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) {
    _VSTD::__destroy_at(__loc);
}

#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) {
  _VSTD::__destroy_at(__loc);
}
#endif

template <class _ForwardIterator>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
void destroy(_ForwardIterator __first, _ForwardIterator __last) {
  (void)_VSTD::__destroy(_VSTD::move(__first), _VSTD::move(__last));
}

template <class _ForwardIterator, class _Size>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
_ForwardIterator destroy_n(_ForwardIterator __first, _Size __n) {
    for (; __n > 0; (void)++__first, --__n)
        _VSTD::__destroy_at(_VSTD::addressof(*__first));
    return __first;
}

#endif // _LIBCPP_STD_VER > 14

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___MEMORY_CONSTRUCT_AT_H