Comment by LexiMax

groan

> When dealing with class hierarchies, destructive move semantics becomes problematic. If you move the base first, then the source has a constructed derived part and a destructed base part. If you move the derived part first then the target has a constructed derived part and a not-yet-constructed base part. Neither option seems viable. Several solutions to this dilemma have been explored.

Add this to my "C++ chose the wrong kind of polymorphism to make first-class" tally.