[libcxx-commits] [libcxx] [libc++] Fix UB in <expected> related to "has value" flag (#68552) (PR #68733)

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@@ -440,9 +399,10 @@ class expected {
       std::destroy_at(std::addressof(__union_.__val_));
     } else {
       std::destroy_at(std::addressof(__union_.__unex_));
-      __has_val_ = true;
     }
-    return *std::construct_at(std::addressof(__union_.__val_), std::forward<_Args>(__args)...);
+    std::construct_at(std::addressof(__union_.__val_), std::forward<_Args>(__args)...);
+    __has_val_ = true;
+    return *std::addressof(__union_.__val_);
----------------
huixie90 wrote:

what is the difference between this and just `return __union_.__val_;` ?
(same question in other places)

https://github.com/llvm/llvm-project/pull/68733