https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79290
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- I forgot to provide the error. For completeness, it's: s.cc: In member function ‘bool Printer<T>::operator()(SongTag)’: s.cc:16:36: error: request for member ‘int (Song::*)(unsigned int) const::__pfn’ in ‘st.SongTag::function()’, which is of non-class type ‘Song::GetFunction {aka int (Song::*)(unsigned int) const}’ return st.function() == &Song::get; ^~~