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54 lines
1.8 KiB
C++
54 lines
1.8 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___UTILITY_NO_DESTROY_H
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#define _LIBCPP___UTILITY_NO_DESTROY_H
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#include <__config>
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#include <__type_traits/is_constant_evaluated.h>
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#include <__utility/forward.h>
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#include <new>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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struct __uninitialized_tag {};
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// This class stores an object of type _Tp but never destroys it.
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//
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// This is akin to using __attribute__((no_destroy)), except that it is possible
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// to control the lifetime of the object with more flexibility by deciding e.g.
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// whether to initialize the object at construction or to defer to a later
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// initialization using __emplace.
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template <class _Tp>
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struct __no_destroy {
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __no_destroy(__uninitialized_tag) : __obj_() {}
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template <class... _Args>
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_LIBCPP_HIDE_FROM_ABI explicit __no_destroy(_Args&&... __args) {
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::new ((void*)__obj_) _Tp(std::forward<_Args>(__args)...);
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}
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template <class... _Args>
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_LIBCPP_HIDE_FROM_ABI _Tp& __emplace(_Args&&... __args) {
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return *(::new ((void*)__obj_) _Tp(std::forward<_Args>(__args)...));
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}
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_LIBCPP_HIDE_FROM_ABI _Tp& __get() { return *reinterpret_cast<_Tp*>(__obj_); }
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_LIBCPP_HIDE_FROM_ABI _Tp const& __get() const { return *reinterpret_cast<const _Tp*>(__obj_); }
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private:
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_ALIGNAS_TYPE(_Tp) char __obj_[sizeof(_Tp)];
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};
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___UTILITY_NO_DESTROY_H
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