https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77528
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to TC from comment #2) > This makes the default constructor implicit, Yes, that was intentional :-) > though that's probably how it > should be anyway. Yes, we missed the container adaptors when fixing https://wg21.link/lwg2193