1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___UTILITY_NO_DESTROY_H
10#define _LIBCPP___UTILITY_NO_DESTROY_H
11
12#include <__config>
13#include <__type_traits/is_constant_evaluated.h>
14#include <__utility/forward.h>
15#include <new>
16
17#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
18# pragma GCC system_header
19#endif
20
21_LIBCPP_BEGIN_NAMESPACE_STD
22
23struct __uninitialized_tag {};
24
25// This class stores an object of type _Tp but never destroys it.
26//
27// This is akin to using __attribute__((no_destroy)), except that it is possible
28// to control the lifetime of the object with more flexibility by deciding e.g.
29// whether to initialize the object at construction or to defer to a later
30// initialization using __emplace.
31template <class _Tp>
32struct __no_destroy {
33 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __no_destroy(__uninitialized_tag) : __obj_() {}
34
35 template <class... _Args>
36 _LIBCPP_HIDE_FROM_ABI explicit __no_destroy(_Args&&... __args) {
37 ::new ((void*)__obj_) _Tp(std::forward<_Args>(__args)...);
38 }
39
40 template <class... _Args>
41 _LIBCPP_HIDE_FROM_ABI _Tp& __emplace(_Args&&... __args) {
42 return *(::new ((void*)__obj_) _Tp(std::forward<_Args>(__args)...));
43 }
44
45 _LIBCPP_HIDE_FROM_ABI _Tp& __get() { return *reinterpret_cast<_Tp*>(__obj_); }
46 _LIBCPP_HIDE_FROM_ABI _Tp const& __get() const { return *reinterpret_cast<const _Tp*>(__obj_); }
47
48private:
49 _ALIGNAS_TYPE(_Tp) char __obj_[sizeof(_Tp)];
50};
51
52_LIBCPP_END_NAMESPACE_STD
53
54#endif // _LIBCPP___UTILITY_NO_DESTROY_H
55