* [committed] libstdc++: Use emplace in std::variant::operator=(T&&) as per LWG 3585
@ 2023-02-02 16:48 Jonathan Wakely
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From: Jonathan Wakely @ 2023-02-02 16:48 UTC (permalink / raw)
To: libstdc++, gcc-patches
Tested powerpc64le-linux. Pushed to trunk.
-- >8 --
This was approved at the October 2021 plenary.
libstdc++-v3/ChangeLog:
* include/std/variant (variant::operator=): Implement resolution
of LWG 3585.
* testsuite/20_util/variant/lwg3585.cc: New test.
---
libstdc++-v3/include/std/variant | 4 +++-
.../testsuite/20_util/variant/lwg3585.cc | 16 ++++++++++++++++
2 files changed, 19 insertions(+), 1 deletion(-)
create mode 100644 libstdc++-v3/testsuite/20_util/variant/lwg3585.cc
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 35781495e31..5155124522f 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1481,7 +1481,9 @@ namespace __variant
|| !is_nothrow_move_constructible_v<_Tj>)
this->emplace<__index>(std::forward<_Tp>(__rhs));
else
- operator=(variant(std::forward<_Tp>(__rhs)));
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 3585. converting assignment with immovable alternative
+ this->emplace<__index>(_Tj(std::forward<_Tp>(__rhs)));
}
return *this;
}
diff --git a/libstdc++-v3/testsuite/20_util/variant/lwg3585.cc b/libstdc++-v3/testsuite/20_util/variant/lwg3585.cc
new file mode 100644
index 00000000000..0cbfc0db7f5
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/variant/lwg3585.cc
@@ -0,0 +1,16 @@
+// { dg-do compile { target c++17 } }
+
+// LWG 3585. Variant converting assignment with immovable alternative
+
+#include <variant>
+#include <string>
+
+struct A {
+ A() = default;
+ A(A&&) = delete;
+};
+
+int main() {
+ std::variant<A, std::string> v;
+ v = "hello";
+}
--
2.39.1
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2023-02-02 16:48 [committed] libstdc++: Use emplace in std::variant::operator=(T&&) as per LWG 3585 Jonathan Wakely
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