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This is the next part of the library changes from P2255R2. This makes INVOKE<R> ill-formed if converting the INVOKE expression to R would bind a reference to a temporary object. The is_invocable_r trait is now false if the invocation would create a dangling reference. This is done by adding the dangling check to the __is_invocable_impl partial specialization used for INVOKE<R> expressions. This change also slightly simplifies the nothrow checking recently added to that partial specialization. This change also removes the is_invocable_r checks from the pre-C++17 implementation of std::__invoke_r, because there is no need for it to be SFINAE-friendly. None of our C++11 and C++14 uses of INVOKE<R> require those constraints. The std::function constructor needs to check is_invocable_r, but that's already done explicitly, so we don't need to recheck when calling __is_invoke_r in std::function::operator(). The other uses of std::__is_invoke_r do not need to be constrained and can just be ill-formed if the INVOKE<R> expression is ill-formed. libstdc++-v3/ChangeLog: PR libstdc++/70692 * include/bits/invoke.h [__cplusplus < 201703] (__invoke_r): Remove is_invocable and is_convertible constraints. * include/std/type_traits (__is_invocable_impl::_S_conv): Use non-deduced context for parameter. (__is_invocable_impl::_S_test): Remove _Check_noex template parameter and use deduced noexcept value in its place. Add bool parameter to detect dangling references. (__is_invocable_impl::type): Adjust call to _S_test to avoid deducing unnecessary noexcept property.. (__is_invocable_impl::__nothrow_type): Rename to ... (__is_invocable_impl::__nothrow_conv): ... this. Adjust call to _S_test to deduce noexcept property. * testsuite/20_util/bind/dangling_ref.cc: New test. * testsuite/20_util/function/cons/70692.cc: New test. * testsuite/20_util/function_objects/invoke/dangling_ref.cc: New test. * testsuite/20_util/is_invocable/dangling_ref.cc: New test. * testsuite/30_threads/packaged_task/cons/dangling_ref.cc: New test.
159 lines
6.0 KiB
C++
159 lines
6.0 KiB
C++
// Implementation of INVOKE -*- C++ -*-
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// Copyright (C) 2016-2022 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file include/bits/invoke.h
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* This is an internal header file, included by other library headers.
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* Do not attempt to use it directly. @headername{functional}
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*/
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#ifndef _GLIBCXX_INVOKE_H
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#define _GLIBCXX_INVOKE_H 1
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#pragma GCC system_header
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#if __cplusplus < 201103L
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# include <bits/c++0x_warning.h>
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#else
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#include <type_traits>
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#include <bits/move.h> // forward
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namespace std _GLIBCXX_VISIBILITY(default)
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{
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_GLIBCXX_BEGIN_NAMESPACE_VERSION
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/**
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* @addtogroup utilities
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* @{
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*/
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// Used by __invoke_impl instead of std::forward<_Tp> so that a
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// reference_wrapper is converted to an lvalue-reference.
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template<typename _Tp, typename _Up = typename __inv_unwrap<_Tp>::type>
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constexpr _Up&&
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__invfwd(typename remove_reference<_Tp>::type& __t) noexcept
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{ return static_cast<_Up&&>(__t); }
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template<typename _Res, typename _Fn, typename... _Args>
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constexpr _Res
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__invoke_impl(__invoke_other, _Fn&& __f, _Args&&... __args)
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{ return std::forward<_Fn>(__f)(std::forward<_Args>(__args)...); }
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template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
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constexpr _Res
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__invoke_impl(__invoke_memfun_ref, _MemFun&& __f, _Tp&& __t,
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_Args&&... __args)
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{ return (__invfwd<_Tp>(__t).*__f)(std::forward<_Args>(__args)...); }
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template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
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constexpr _Res
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__invoke_impl(__invoke_memfun_deref, _MemFun&& __f, _Tp&& __t,
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_Args&&... __args)
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{
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return ((*std::forward<_Tp>(__t)).*__f)(std::forward<_Args>(__args)...);
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}
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template<typename _Res, typename _MemPtr, typename _Tp>
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constexpr _Res
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__invoke_impl(__invoke_memobj_ref, _MemPtr&& __f, _Tp&& __t)
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{ return __invfwd<_Tp>(__t).*__f; }
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template<typename _Res, typename _MemPtr, typename _Tp>
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constexpr _Res
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__invoke_impl(__invoke_memobj_deref, _MemPtr&& __f, _Tp&& __t)
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{ return (*std::forward<_Tp>(__t)).*__f; }
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/// Invoke a callable object.
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template<typename _Callable, typename... _Args>
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constexpr typename __invoke_result<_Callable, _Args...>::type
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__invoke(_Callable&& __fn, _Args&&... __args)
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noexcept(__is_nothrow_invocable<_Callable, _Args...>::value)
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{
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using __result = __invoke_result<_Callable, _Args...>;
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using __type = typename __result::type;
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using __tag = typename __result::__invoke_type;
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return std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
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std::forward<_Args>(__args)...);
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}
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#if __cplusplus >= 201703L
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// INVOKE<R>: Invoke a callable object and convert the result to R.
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template<typename _Res, typename _Callable, typename... _Args>
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constexpr enable_if_t<is_invocable_r_v<_Res, _Callable, _Args...>, _Res>
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__invoke_r(_Callable&& __fn, _Args&&... __args)
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noexcept(is_nothrow_invocable_r_v<_Res, _Callable, _Args...>)
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{
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using __result = __invoke_result<_Callable, _Args...>;
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using __type = typename __result::type;
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using __tag = typename __result::__invoke_type;
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if constexpr (is_void_v<_Res>)
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std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
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std::forward<_Args>(__args)...);
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else
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return std::__invoke_impl<__type>(__tag{},
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std::forward<_Callable>(__fn),
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std::forward<_Args>(__args)...);
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}
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#else // C++11 or C++14
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// This is a non-SFINAE-friendly std::invoke_r<R>(fn, args...) for C++11/14.
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// It's used in std::function, std::bind, and std::packaged_task. Only
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// std::function is constrained on is_invocable_r, but that is checked on
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// construction so doesn't need to be checked again when calling __invoke_r.
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// Consequently, these __invoke_r overloads do not check for invocable
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// arguments, nor check that the invoke result is convertible to R.
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// INVOKE<R>: Invoke a callable object and convert the result to R.
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template<typename _Res, typename _Callable, typename... _Args>
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constexpr __enable_if_t<!is_void<_Res>::value, _Res>
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__invoke_r(_Callable&& __fn, _Args&&... __args)
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{
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using __result = __invoke_result<_Callable, _Args...>;
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using __type = typename __result::type;
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static_assert(!__reference_converts_from_temporary(_Res, __type),
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"INVOKE<R> must not create a dangling reference");
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using __tag = typename __result::__invoke_type;
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return std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
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std::forward<_Args>(__args)...);
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}
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// INVOKE<R> when R is cv void
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template<typename _Res, typename _Callable, typename... _Args>
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_GLIBCXX14_CONSTEXPR __enable_if_t<is_void<_Res>::value, _Res>
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__invoke_r(_Callable&& __fn, _Args&&... __args)
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{
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using __result = __invoke_result<_Callable, _Args...>;
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using __type = typename __result::type;
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using __tag = typename __result::__invoke_type;
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std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
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std::forward<_Args>(__args)...);
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}
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#endif // C++11 or C++14
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_GLIBCXX_END_NAMESPACE_VERSION
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} // namespace std
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#endif // C++11
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#endif // _GLIBCXX_INVOKE_H
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