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 <__new/placement_new_delete.h>
14#include <__utility/forward.h>
15
16#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
17# pragma GCC system_header
18#endif
19
20_LIBCPP_BEGIN_NAMESPACE_STD
21
22struct __uninitialized_tag {};
23
24// This class stores an object of type _Tp but never destroys it.
25//
26// This is akin to using __attribute__((no_destroy)), except that it is possible
27// to control the lifetime of the object with more flexibility by deciding e.g.
28// whether to initialize the object at construction or to defer to a later
29// initialization using __emplace.
30template <class _Tp>
31struct __no_destroy {
32 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __no_destroy(__uninitialized_tag) : __obj_() {}
33
34 template <class... _Args>
35 _LIBCPP_HIDE_FROM_ABI explicit __no_destroy(_Args&&... __args) {
36 ::new ((void*)__obj_) _Tp(std::forward<_Args>(__args)...);
37 }
38
39 template <class... _Args>
40 _LIBCPP_HIDE_FROM_ABI _Tp& __emplace(_Args&&... __args) {
41 return *(::new ((void*)__obj_) _Tp(std::forward<_Args>(__args)...));
42 }
43
44 _LIBCPP_HIDE_FROM_ABI _Tp& __get() { return *reinterpret_cast<_Tp*>(__obj_); }
45 _LIBCPP_HIDE_FROM_ABI _Tp const& __get() const { return *reinterpret_cast<const _Tp*>(__obj_); }
46
47private:
48 _ALIGNAS_TYPE(_Tp) char __obj_[sizeof(_Tp)];
49};
50
51_LIBCPP_END_NAMESPACE_STD
52
53#endif // _LIBCPP___UTILITY_NO_DESTROY_H
54