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* [gcc/devel/gccgo] libstdc++: Fix constraints on std::compare_three_way
@ 2020-07-12 17:13 Ian Lance Taylor
0 siblings, 0 replies; only message in thread
From: Ian Lance Taylor @ 2020-07-12 17:13 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:e1e9e8d7aa7bf1b0d3de34345b6c649e07da7a1e
commit e1e9e8d7aa7bf1b0d3de34345b6c649e07da7a1e
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Apr 14 21:58:03 2020 +0100
libstdc++: Fix constraints on std::compare_three_way
My "simplification" of std::compare_three_way's constraints in commit
f214ffb336d582a66149068a2a96b7fcf395b5de was incorrect, because
std::three_way_comparable_with imposes additional restrictions beyond
the <=> expression being valid.
* libsupc++/compare (compare_three_way): Fix constraint so that
BUILTIN-PTR-THREE-WAY does not require three_way_comparable_with.
* testsuite/18_support/comparisons/object/builtin-ptr-three-way.cc:
New test.
Diff:
---
libstdc++-v3/ChangeLog | 5 +++
libstdc++-v3/libsupc++/compare | 8 ++--
.../comparisons/object/builtin-ptr-three-way.cc | 45 ++++++++++++++++++++++
3 files changed, 55 insertions(+), 3 deletions(-)
diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 417c8c440c6..0283cf313f0 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,10 @@
2020-04-14 Jonathan Wakely <jwakely@redhat.com>
+ * libsupc++/compare (compare_three_way): Fix constraint so that
+ BUILTIN-PTR-THREE-WAY does not require three_way_comparable_with.
+ * testsuite/18_support/comparisons/object/builtin-ptr-three-way.cc:
+ New test.
+
PR libstdc++/94562
* include/bits/shared_ptr.h (operator<=>): Define for C++20.
* include/bits/shared_ptr_base.h (operator<=>): Likewise.
diff --git a/libstdc++-v3/libsupc++/compare b/libstdc++-v3/libsupc++/compare
index 5f1df19e445..e5fb322ed9e 100644
--- a/libstdc++-v3/libsupc++/compare
+++ b/libstdc++-v3/libsupc++/compare
@@ -481,13 +481,14 @@ namespace std
// BUILTIN-PTR-THREE-WAY(T, U)
template<typename _Tp, typename _Up>
concept __3way_builtin_ptr_cmp
- = three_way_comparable_with<_Tp, _Up>
+ = requires(_Tp&& __t, _Up&& __u)
+ { static_cast<_Tp&&>(__t) <=> static_cast<_Up&&>(__u); }
&& convertible_to<_Tp, const volatile void*>
&& convertible_to<_Up, const volatile void*>
&& ! requires(_Tp&& __t, _Up&& __u)
- { operator<=>(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u)); }
+ { operator<=>(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u)); }
&& ! requires(_Tp&& __t, _Up&& __u)
- { static_cast<_Tp&&>(__t).operator<=>(static_cast<_Up&&>(__u)); };
+ { static_cast<_Tp&&>(__t).operator<=>(static_cast<_Up&&>(__u)); };
} // namespace __detail
// [cmp.object], typename compare_three_way
@@ -495,6 +496,7 @@ namespace std
{
template<typename _Tp, typename _Up>
requires three_way_comparable_with<_Tp, _Up>
+ || __detail::__3way_builtin_ptr_cmp<_Tp, _Up>
constexpr auto
operator()(_Tp&& __t, _Up&& __u) const
noexcept(noexcept(std::declval<_Tp>() <=> std::declval<_Up>()))
diff --git a/libstdc++-v3/testsuite/18_support/comparisons/object/builtin-ptr-three-way.cc b/libstdc++-v3/testsuite/18_support/comparisons/object/builtin-ptr-three-way.cc
new file mode 100644
index 00000000000..38b3c6e3211
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/comparisons/object/builtin-ptr-three-way.cc
@@ -0,0 +1,45 @@
+// Copyright (C) 2020 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++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <compare>
+
+void
+test01()
+{
+ struct X
+ {
+ operator int() const { return 0; }
+ operator long*() const { return nullptr; }
+ } x;
+
+ // Not three-way-comparable because of ambiguous conversion to int or long*:
+ static_assert( ! std::three_way_comparable<X> );
+
+ // And therefore X is not three-way-comparable-with anything else
+ // (because std::three_way_comparable_with<X, Y> requires that both
+ // three_way_comparable<X> and three_way_comparable<Y> are true).
+ static_assert( ! std::three_way_comparable_with<X, long*> );
+
+ long l;
+ // But <=> is valid and resolves to a builtin operator comparing pointers:
+ auto c = &l <=> x;
+ // So std::compare_three_way should be usable:
+ auto c2 = std::compare_three_way()(&l, x);
+}
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