From f13f9c99dbee9c495955a430dd10bdb24a16f24a Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Thu, 19 May 2022 13:26:49 +0100
Subject: [PATCH] libstdc++: Implement LWG 3683 for pmr::polymorphic_allocator
This issue has recently been moved to Tentatively Ready, and seems
uncontroversial. This allows equality comparison with types that are
convertible to pmr::polymorphic_allocator, which fail deduction for the
existing equality operator.
libstdc++-v3/ChangeLog:
* include/std/memory_resource (polymorphic_allocator): Add
non-template equality operator, as proposed for LWG 3683.
* testsuite/20_util/polymorphic_allocator/lwg3683.cc: New test.
---
libstdc++-v3/include/std/memory_resource | 16 ++++++++++++++++
.../20_util/polymorphic_allocator/lwg3683.cc | 13 +++++++++++++
2 files changed, 29 insertions(+)
create mode 100644 libstdc++-v3/testsuite/20_util/polymorphic_allocator/lwg3683.cc
diff --git a/libstdc++-v3/include/std/memory_resource b/libstdc++-v3/include/std/memory_resource
index 88e8abd60fad..745422ad5eba 100644
--- a/libstdc++-v3/include/std/memory_resource
+++ b/libstdc++-v3/include/std/memory_resource
@@ -356,6 +356,22 @@ namespace pmr
__attribute__((__returns_nonnull__))
{ return _M_resource; }
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 3683. operator== for polymorphic_allocator cannot deduce template arg
+ [[nodiscard]]
+ friend bool
+ operator==(const polymorphic_allocator& __a,
+ const polymorphic_allocator& __b) noexcept
+ { return *__a.resource() == *__b.resource(); }
+
+#if __cpp_impl_three_way_comparison < 201907L
+ [[nodiscard]]
+ friend bool
+ operator!=(const polymorphic_allocator& __a,
+ const polymorphic_allocator& __b) noexcept
+ { return !(__a == __b); }
+#endif
+
private:
#if ! __cpp_lib_make_obj_using_allocator
using __uses_alloc1_ = __uses_alloc1<polymorphic_allocator>;
diff --git a/libstdc++-v3/testsuite/20_util/polymorphic_allocator/lwg3683.cc b/libstdc++-v3/testsuite/20_util/polymorphic_allocator/lwg3683.cc
new file mode 100644
index 000000000000..acc91f540b5e
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/polymorphic_allocator/lwg3683.cc
@@ -0,0 +1,13 @@
+// { dg-do compile { target c++17 } }
+
+#include <memory_resource>
+
+bool
+test_lwg3683(const std::pmr::polymorphic_allocator<int>& a)
+{
+ if (a == std::pmr::get_default_resource())
+ return true;
+ if (std::pmr::get_default_resource() != a)
+ return false;
+ throw a;
+}
--
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