https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69098
--- Comment #1 from hir...@trash-mail.com --- The error message I got, copied from Wandbox: prog.cc: In instantiation of 'static void Specializer::InnerClassTempl<<anonymous> >::InnerMemberFn() [with unsigned int <anonymous> = 0u]': prog.cc:16:24: required from here prog.cc:33:36: error: 'template<bool P> constexpr void (Specializer::* const SpecPerType<Specializer>::SpecMbrFnPtr)()<<anonymous> >' is not a function template typename Spec::FnType ErrorSite = Spec::template SpecMbrFnPtr<true>; ^~~~ prog.cc:33:36: error: 'SpecMbrFnPtr<true>' is not a member of 'Spec {aka SpecPerType<Specializer>}'