http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57684
--- Comment #2 from Francesco Biscani <bluescarni at gmail dot com> --- (In reply to Jonathan Wakely from comment #1) > I think the problem is that unordered_map requires its template arguments to > be complete at the time of instantiation, otherwise it's undefined behaviour. > > When the static member is instantiated the type Derived is not complete, > because base<derived> is instantiated before the body of derived. > > So although it would be nice if this worked, I think it technically relies > on undefined behaviour. Thanks for the quick reply! I understand this might be a bit OT here, but would wrapping the static member in an std::unique_ptr avoid UB?
