https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83000
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to Andrew Pinski from comment #4) > (In reply to Martin Liška from comment #3) > > (In reply to Andrew Pinski from comment #2) > > > Seems fixed in GCC 10. > > > > Are you sure, all releases I have reject the code. > > You need -std=c++2a or -std=c++20 or -fconcepts to support concepts :). GCC 9 does not enable concepts for -std=c++2a so you need -fconcepts really.
