* doc/xml/manual/intro.xml: Document LWG 2993 change.
* include/bits/refwrap.h (reference_wrapper(_Tp&)): Remove.
(reference_wrapper(_Tp&&)): Remove.
(reference_wrapper<_Up>(_Up&&)): Define new constructor as constrained
template.
(reference_wrapper): Add deduction guide.
* testsuite/20_util/reference_wrapper/deduction.cc: New.
* testsuite/20_util/reference_wrapper/lwg2993.cc: New.
From-SVN: r261632
2018-06-15 Jonathan Wakely <jwakely@redhat.com>
+ LWG 2993 reference_wrapper<T> conversion from T&&
+ * doc/xml/manual/intro.xml: Document LWG 2993 change.
+ * include/bits/refwrap.h (reference_wrapper(_Tp&)): Remove.
+ (reference_wrapper(_Tp&&)): Remove.
+ (reference_wrapper<_Up>(_Up&&)): Define new constructor as constrained
+ template.
+ (reference_wrapper): Add deduction guide.
+ * testsuite/20_util/reference_wrapper/deduction.cc: New.
+ * testsuite/20_util/reference_wrapper/lwg2993.cc: New.
+
LWG 3039 Unnecessary decay in thread and packaged_task
* include/std/future (__constrain_pkgdtask): Replace with ...
(packaged_task::__not_same): New alias template, using
<listitem><para>Add noexcept.
</para></listitem></varlistentry>
+ <varlistentry xml:id="manual.bugs.dr2993"><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="&DR;#2993">2993</link>:
+ <emphasis><code>reference_wrapper<T></code> conversion from <code>T&&</code>
+ </emphasis>
+ </term>
+ <listitem><para>Replaced the constructors with a constrained template,
+ to prevent participation in overload resolution when not valid.
+ </para></listitem></varlistentry>
+
<varlistentry xml:id="manual.bugs.dr3074"><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="&DR;#3074">3074</link>:
<emphasis>Non-member functions for <code>valarray</code> should only deduce from the <code>valarray</code>
</emphasis>
{
_Tp* _M_data;
+ static _Tp* _S_fun(_Tp& __r) noexcept { return std::__addressof(__r); }
+ static void _S_fun(_Tp&&) = delete;
+
+ template<typename _Up, typename _Up2 = __remove_cvref_t<_Up>>
+ using __not_same
+ = typename enable_if<!is_same<reference_wrapper, _Up2>::value>::type;
+
public:
typedef _Tp type;
- reference_wrapper(_Tp& __indata) noexcept
- : _M_data(std::__addressof(__indata))
- { }
-
- reference_wrapper(_Tp&&) = delete;
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 2993. reference_wrapper<T> conversion from T&&
+ // 3041. Unnecessary decay in reference_wrapper
+ template<typename _Up, typename = __not_same<_Up>, typename
+ = decltype(reference_wrapper::_S_fun(std::declval<_Up>()))>
+ reference_wrapper(_Up&& __uref)
+ noexcept(noexcept(reference_wrapper::_S_fun(std::declval<_Up>())))
+ : _M_data(reference_wrapper::_S_fun(std::forward<_Up>(__uref)))
+ { }
reference_wrapper(const reference_wrapper&) = default;
}
};
+#if __cpp_deduction_guides
+ template<typename _Tp>
+ reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
+#endif
/// Denotes a reference should be taken to a variable.
template<typename _Tp>
--- /dev/null
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do compile { target c++17 } }
+
+#include <functional>
+
+void
+test01()
+{
+ int i = 0;
+ std::reference_wrapper rw0(i);
+ [[maybe_unused]] std::reference_wrapper<int>* p0 = &rw0;
+ [[maybe_unused]] int& r0 = rw0;
+
+ std::reference_wrapper rw1(rw0);
+ [[maybe_unused]] std::reference_wrapper<int>* p1 = &rw1;
+ [[maybe_unused]] int& r1 = rw1;
+}
+
+void
+test02()
+{
+ const int i = 0;
+ std::reference_wrapper rw0(i);
+ [[maybe_unused]] std::reference_wrapper<const int>* p0 = &rw0;
+
+ std::reference_wrapper rw1(rw0);
+ [[maybe_unused]] std::reference_wrapper<const int>* p1 = &rw1;
+}
--- /dev/null
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do compile { target c++11 } }
+
+#include <functional>
+
+// LWG 2993. reference_wrapper<T> conversion from T&&
+
+static_assert(std::is_convertible<std::reference_wrapper<int>,
+ std::reference_wrapper<const int>>::value,
+ "LWG 2993 enables qualification conversions");
+
+// The comments below are taken from the issue discussion and describe the
+// behaviour before the resolution of LWG 2993. There should be no errors now.
+
+struct convertible_from_int { convertible_from_int(int) { } };
+
+void
+test01()
+{
+
+ void meow(std::reference_wrapper<int>); //#1
+ void meow(convertible_from_int); //#2
+ // error, ambiguous; would unambiguously call #2 if #1 instead took int&
+ meow(0);
+}
+
+void
+test02()
+{
+ std::reference_wrapper<int> purr();
+
+ // error, ambiguous: ICS exists from int prvalue to
+ // reference_wrapper<int> and from reference_wrapper<int> to int
+ auto x = true ? purr() : 0;
+
+ // error: no member 'type' because the conditional
+ // expression is ill-formed
+ using t = std::common_type_t<std::reference_wrapper<int>, int>;
+}
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