https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78470
Markus Trippelsdorf <trippels at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED CC| |trippels at gcc dot gnu.org Resolution|--- |INVALID --- Comment #1 from Markus Trippelsdorf <trippels at gcc dot gnu.org> --- Yes, this is expected. You can either use -std=c++1z. Otherwise, if a constexpr static data member is odr-used, a definition at namespace scope is required.