48c805bafd
The diagnostics for `enable_if_t` are extremely opaque: ``` error: no matching function for call to 'bind_front' note: candidate template ignored: requirement 'integral_constant<bool, false>::value' was not satisfied ``` Using requires-expressions gives us a little more context: ``` error: no matching function for call to 'bind_front' note: candidate template ignored: constraints not satisfied note: because 'is_constructible_v<decay_t<T &>, T &>' evaluated to false ``` Pull request: #68249
60 lines
2.8 KiB
C++
60 lines
2.8 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___FUNCTIONAL_BIND_BACK_H
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#define _LIBCPP___FUNCTIONAL_BIND_BACK_H
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#include <__config>
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#include <__functional/invoke.h>
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#include <__functional/perfect_forward.h>
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#include <__type_traits/decay.h>
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#include <__utility/forward.h>
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#include <__utility/integer_sequence.h>
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#include <tuple>
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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 >= 20
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template <size_t _NBound, class = make_index_sequence<_NBound>>
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struct __bind_back_op;
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template <size_t _NBound, size_t ..._Ip>
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struct __bind_back_op<_NBound, index_sequence<_Ip...>> {
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template <class _Fn, class _BoundArgs, class... _Args>
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_LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Fn&& __f, _BoundArgs&& __bound_args, _Args&&... __args) const
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noexcept(noexcept(_VSTD::invoke(_VSTD::forward<_Fn>(__f), _VSTD::forward<_Args>(__args)..., _VSTD::get<_Ip>(_VSTD::forward<_BoundArgs>(__bound_args))...)))
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-> decltype( _VSTD::invoke(_VSTD::forward<_Fn>(__f), _VSTD::forward<_Args>(__args)..., _VSTD::get<_Ip>(_VSTD::forward<_BoundArgs>(__bound_args))...))
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{ return _VSTD::invoke(_VSTD::forward<_Fn>(__f), _VSTD::forward<_Args>(__args)..., _VSTD::get<_Ip>(_VSTD::forward<_BoundArgs>(__bound_args))...); }
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};
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template <class _Fn, class _BoundArgs>
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struct __bind_back_t : __perfect_forward<__bind_back_op<tuple_size_v<_BoundArgs>>, _Fn, _BoundArgs> {
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using __perfect_forward<__bind_back_op<tuple_size_v<_BoundArgs>>, _Fn, _BoundArgs>::__perfect_forward;
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};
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template <class _Fn, class... _Args>
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requires is_constructible_v<decay_t<_Fn>, _Fn> && is_move_constructible_v<decay_t<_Fn>> &&
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(is_constructible_v<decay_t<_Args>, _Args> && ...) && (is_move_constructible_v<decay_t<_Args>> && ...)
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_LIBCPP_HIDE_FROM_ABI
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constexpr auto __bind_back(_Fn&& __f, _Args&&... __args)
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noexcept(noexcept(__bind_back_t<decay_t<_Fn>, tuple<decay_t<_Args>...>>(_VSTD::forward<_Fn>(__f), _VSTD::forward_as_tuple(_VSTD::forward<_Args>(__args)...))))
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-> decltype( __bind_back_t<decay_t<_Fn>, tuple<decay_t<_Args>...>>(_VSTD::forward<_Fn>(__f), _VSTD::forward_as_tuple(_VSTD::forward<_Args>(__args)...)))
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{ return __bind_back_t<decay_t<_Fn>, tuple<decay_t<_Args>...>>(_VSTD::forward<_Fn>(__f), _VSTD::forward_as_tuple(_VSTD::forward<_Args>(__args)...)); }
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#endif // _LIBCPP_STD_VER >= 20
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___FUNCTIONAL_BIND_BACK_H
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