6157dbe48c
This allows forwarding an object as a specific type. This is usually useful when using `deducing this` to avoid calling any functions in a deriving class.
64 lines
2.1 KiB
C++
64 lines
2.1 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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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_FORWARD_LIKE_H
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#define _LIBCPP___UTILITY_FORWARD_LIKE_H
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#include <__config>
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#include <__type_traits/conditional.h>
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#include <__type_traits/is_base_of.h>
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#include <__type_traits/is_const.h>
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#include <__type_traits/is_reference.h>
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#include <__type_traits/remove_reference.h>
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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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#if _LIBCPP_STD_VER >= 23
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template <class _Ap, class _Bp>
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using _CopyConst = _If<is_const_v<_Ap>, const _Bp, _Bp>;
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template <class _Ap, class _Bp>
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using _OverrideRef = _If<is_rvalue_reference_v<_Ap>, remove_reference_t<_Bp>&&, _Bp&>;
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template <class _Ap, class _Bp>
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using _ForwardLike = _OverrideRef<_Ap&&, _CopyConst<remove_reference_t<_Ap>, remove_reference_t<_Bp>>>;
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template <class _Tp, class _Up>
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[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto
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forward_like(_LIBCPP_LIFETIMEBOUND _Up&& __ux) noexcept -> _ForwardLike<_Tp, _Up> {
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return static_cast<_ForwardLike<_Tp, _Up>>(__ux);
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}
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// This function is used for `deducing this` cases where you want to make sure the operation is performed on the class
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// itself and not on a derived class. For example
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// struct S {
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// template <class Self>
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// void func(Self&& self) {
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// // This will always call `do_something` of S instead of any class derived from S.
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// std::__forward_as<Self, S>(self).do_something();
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// }
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// };
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template <class _Tp, class _As, class _Up>
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[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _ForwardLike<_Tp, _As>
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__forward_as(_LIBCPP_LIFETIMEBOUND _Up&& __val) noexcept {
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static_assert(is_base_of_v<_As, remove_reference_t<_Up>>);
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return static_cast<_ForwardLike<_Tp, _As>>(__val);
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}
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#endif // _LIBCPP_STD_VER >= 23
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___UTILITY_FORWARD_LIKE_H
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