[Bug libstdc++/51558] Declaration of unspecialized std::hash<_Tp>::operator()(_Tp) turns compile-time errors into link-time errors

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51558

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-12-14 
22:57:11 UTC ---
Could we put a static_assert in the default operator() definition?