libcxx/include/__utility/forward_like.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___UTILITY_FORWARD_LIKE_H
  11 #define _LIBCPP___UTILITY_FORWARD_LIKE_H
  12
  13 #include <__config>
  14 #include <__type_traits/conditional.h>
  15 #include <__type_traits/is_const.h>
  16 #include <__type_traits/is_reference.h>
  17 #include <__type_traits/remove_reference.h>
  18
  19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  20 #  pragma GCC system_header
  21 #endif
  22
  23 _LIBCPP_BEGIN_NAMESPACE_STD
  24
  25 #if _LIBCPP_STD_VER >= 23
  26
  27 template <class _Ap, class _Bp>
  28 using _CopyConst = _If<is_const_v<_Ap>, const _Bp, _Bp>;
  29
  30 template <class _Ap, class _Bp>
  31 using _OverrideRef = _If<is_rvalue_reference_v<_Ap>, remove_reference_t<_Bp>&&, _Bp&>;
  32
  33 template <class _Ap, class _Bp>
  34 using _ForwardLike = _OverrideRef<_Ap&&, _CopyConst<remove_reference_t<_Ap>, remove_reference_t<_Bp>>>;
  35
  36 template <class _Tp, class _Up>
  37 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto forward_like(_LIBCPP_LIFETIMEBOUND _Up&& __ux) noexcept
  38     -> _ForwardLike<_Tp, _Up> {
  39   return static_cast<_ForwardLike<_Tp, _Up>>(__ux);
  40 }
  41
  42 #endif // _LIBCPP_STD_VER >= 23
  43
  44 _LIBCPP_END_NAMESPACE_STD
  45
  46 #endif // _LIBCPP___UTILITY_FORWARD_LIKE_H