Why aren't container move assignment operators noexcept?

Question

I noticed that std::string\'s (really std::basic_string\'s) move assignment operator is noexcept. That makes sense to me. But then I

Answer 1

The move assignment operator in container classes is defined to be noexcept because many containers are designed to implement the strong exception safety guarantee. Containers implement the strong exception safety guarantee because back before there were move assignment operators, the container had to be copied. If anything went wrong with the copy, the new storage was deleted and the container remained unchanged. Now we're stuck with that behavior. If the move assignment op is not noexcept, the slower copy assignment operator is invoked instead.