[libcxx-commits] [libcxx] [libc++] Avoid type-punning between __value_type and pair (PR #134819)

[Nikolas Klauser via libcxx-commits]

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@@ -1276,6 +1267,32 @@ private:
   }
   _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__tree&, false_type) _NOEXCEPT {}
 
+  template <class _From, __enable_if_t<__is_pair_v<__remove_cvref_t<_From> >, int> = 0>
+  _LIBCPP_HIDE_FROM_ABI static void __assign_value(__get_node_value_type_t<value_type>& __lhs, _From&& __rhs) {
+    using __punned_type = pair<typename _NodeTypes::key_type, typename _NodeTypes::mapped_type>;
+
+    reinterpret_cast<__punned_type&>(__lhs) = reinterpret_cast<__copy_cvref_t<_From, __punned_type>&&>(__rhs);
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philnik777 wrote:

Sorry, I might have misunderstood you. Are you suggesting that I should assign the values individually instead of doing the `reinterpret_cast`?

https://github.com/llvm/llvm-project/pull/134819