https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99160
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jonathan Wakely from comment #2) > he using-declaration finds a class and a function, and ignores the class, See [namepace.udecl] p1 and [basic.lookup.general] p4.