libcxx/include/__utility/exchange.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___UTILITY_EXCHANGE_H
  10 #define _LIBCPP___UTILITY_EXCHANGE_H
  11
  12 #include <__config>
  13 #include <__type_traits/is_nothrow_assignable.h>
  14 #include <__type_traits/is_nothrow_move_constructible.h>
  15 #include <__utility/forward.h>
  16 #include <__utility/move.h>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #  pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_PUSH_MACROS
  23 #include <__undef_macros>
  24
  25 _LIBCPP_BEGIN_NAMESPACE_STD
  26
  27 #if _LIBCPP_STD_VER >= 14
  28 template<class _T1, class _T2 = _T1>
  29 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
  30 _T1 exchange(_T1& __obj, _T2&& __new_value)
  31     noexcept(is_nothrow_move_constructible<_T1>::value && is_nothrow_assignable<_T1&, _T2>::value)
  32 {
  33     _T1 __old_value = _VSTD::move(__obj);
  34     __obj = _VSTD::forward<_T2>(__new_value);
  35     return __old_value;
  36 }
  37 #endif // _LIBCPP_STD_VER >= 14
  38
  39 _LIBCPP_END_NAMESPACE_STD
  40
  41 _LIBCPP_POP_MACROS
  42
  43 #endif // _LIBCPP___UTILITY_EXCHANGE_H