libcxx/include/__memory/temp_value.h

   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___MEMORY_TEMP_VALUE_H
  10 #define _LIBCPP___MEMORY_TEMP_VALUE_H
  11
  12 #include <__config>
  13 #include <__memory/addressof.h>
  14 #include <__memory/allocator_traits.h>
  15 #include <__type_traits/aligned_storage.h>
  16 #include <__utility/forward.h>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #  pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_BEGIN_NAMESPACE_STD
  23
  24 template <class _Tp, class _Alloc>
  25 struct __temp_value {
  26     typedef allocator_traits<_Alloc> _Traits;
  27
  28 #ifdef _LIBCPP_CXX03_LANG
  29     typename aligned_storage<sizeof(_Tp), _LIBCPP_ALIGNOF(_Tp)>::type __v;
  30 #else
  31     union { _Tp __v; };
  32 #endif
  33     _Alloc &__a;
  34
  35     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp *__addr() {
  36 #ifdef _LIBCPP_CXX03_LANG
  37         return reinterpret_cast<_Tp*>(std::addressof(__v));
  38 #else
  39         return std::addressof(__v);
  40 #endif
  41     }
  42
  43     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp & get() { return *__addr(); }
  44
  45     template<class... _Args>
  46     _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI
  47     _LIBCPP_CONSTEXPR_SINCE_CXX20 __temp_value(_Alloc &__alloc, _Args&& ... __args) : __a(__alloc) {
  48       _Traits::construct(__a, __addr(), std::forward<_Args>(__args)...);
  49     }
  50
  51     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__temp_value() { _Traits::destroy(__a, __addr()); }
  52 };
  53
  54 _LIBCPP_END_NAMESPACE_STD
  55
  56 #endif // _LIBCPP___MEMORY_TEMP_VALUE_H