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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-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___CXX03___UTILITY_NO_DESTROY_H10#define _LIBCPP___CXX03___UTILITY_NO_DESTROY_H11 12#include <__cxx03/__config>13#include <__cxx03/__type_traits/is_constant_evaluated.h>14#include <__cxx03/__utility/forward.h>15#include <__cxx03/new>16 17#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)18# pragma GCC system_header19#endif20 21_LIBCPP_BEGIN_NAMESPACE_STD22 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 possible28// 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 later30// initialization using __emplace.31template <class _Tp>32struct __no_destroy {33 _LIBCPP_HIDE_FROM_ABI 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_STD53 54#endif // _LIBCPP___CXX03___UTILITY_NO_DESTROY_H55