__cxx03/__utility/forward_like.h

0001 // -*- C++ -*-
0002 //===----------------------------------------------------------------------===//
0003 //
0004 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0005 // See https://llvm.org/LICENSE.txt for license information.
0006 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0007 //
0008 //===----------------------------------------------------------------------===//
0009
0010 #ifndef _LIBCPP___CXX03___UTILITY_FORWARD_LIKE_H
0011 #define _LIBCPP___CXX03___UTILITY_FORWARD_LIKE_H
0012
0013 #include <__cxx03/__config>
0014 #include <__cxx03/__type_traits/conditional.h>
0015 #include <__cxx03/__type_traits/is_const.h>
0016 #include <__cxx03/__type_traits/is_reference.h>
0017 #include <__cxx03/__type_traits/remove_reference.h>
0018
0019 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0020 #  pragma GCC system_header
0021 #endif
0022
0023 _LIBCPP_BEGIN_NAMESPACE_STD
0024
0025 #if _LIBCPP_STD_VER >= 23
0026
0027 template <class _Ap, class _Bp>
0028 using _CopyConst = _If<is_const_v<_Ap>, const _Bp, _Bp>;
0029
0030 template <class _Ap, class _Bp>
0031 using _OverrideRef = _If<is_rvalue_reference_v<_Ap>, remove_reference_t<_Bp>&&, _Bp&>;
0032
0033 template <class _Ap, class _Bp>
0034 using _ForwardLike = _OverrideRef<_Ap&&, _CopyConst<remove_reference_t<_Ap>, remove_reference_t<_Bp>>>;
0035
0036 template <class _Tp, class _Up>
0037 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto
0038 forward_like(_LIBCPP_LIFETIMEBOUND _Up&& __ux) noexcept -> _ForwardLike<_Tp, _Up> {
0039   return static_cast<_ForwardLike<_Tp, _Up>>(__ux);
0040 }
0041
0042 #endif // _LIBCPP_STD_VER >= 23
0043
0044 _LIBCPP_END_NAMESPACE_STD
0045
0046 #endif // _LIBCPP___CXX03___UTILITY_FORWARD_LIKE_H