http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57049
--- Comment #1 from Tudor Bosman <tudorb at fb dot com> 2013-04-23 15:54:18 UTC --- Actually, I'll take this back. I don't believe this is a bug. 17.6.4.9 constraints arguments passed to STL functions. So if there is a library function that takes a rvalue argument (such as string::operator=(string&& other)), then the library is free to assume that the argument doesn't alias (so &other != this). So the assertion in basic_fbstring is correct. The default implementation of swap() does self-move assignment. That would be illegal if the types were MoveAssignable STL types (because then they'd call T::operator=(T&&) which would be illegal according to 17.6.4.9) BUT ALL STL TYPES HAVE SPECIALIZED IMPLEMENTATIONS OF SWAP which don't do self move assignment. So the default swap() will do self-move-assignment on user types, but there's no language in the standard that bans self-move-assignment there.
