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
58 lines
2.0 KiB
C++
58 lines
2.0 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_FRONT_H
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#define _LIBCPP___FUNCTIONAL_BIND_FRONT_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/conjunction.h>
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#include <__type_traits/decay.h>
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#include <__type_traits/enable_if.h>
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#include <__type_traits/is_constructible.h>
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#include <__type_traits/is_move_constructible.h>
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#include <__utility/forward.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 >= 20
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struct __bind_front_op {
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template <class ..._Args>
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_LIBCPP_HIDE_FROM_ABI
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constexpr auto operator()(_Args&& ...__args) const
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noexcept(noexcept(_VSTD::invoke(_VSTD::forward<_Args>(__args)...)))
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-> decltype( _VSTD::invoke(_VSTD::forward<_Args>(__args)...))
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{ return _VSTD::invoke(_VSTD::forward<_Args>(__args)...); }
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};
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template <class _Fn, class ..._BoundArgs>
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struct __bind_front_t : __perfect_forward<__bind_front_op, _Fn, _BoundArgs...> {
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using __perfect_forward<__bind_front_op, _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_front(_Fn&& __f, _Args&&... __args) {
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return __bind_front_t<decay_t<_Fn>, decay_t<_Args>...>(_VSTD::forward<_Fn>(__f), _VSTD::forward<_Args>(__args)...);
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}
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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_FRONT_H
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