https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115209
--- Comment #8 from Patrick Palka <ppalka at gcc dot gnu.org> --- (In reply to 康桓瑋 from comment #7) > (In reply to 康桓瑋 from comment #6) > > (In reply to Patrick Palka from comment #5) > > > (In reply to 康桓瑋 from comment #4) > > > > > Our concat_view implementation is accidentally based off of an > > > > > older > > > > > revision of the paper, P2542R7 instead of R8. As far as I can > > > > > tell the > > > > > only semantic change in the final revision is the relaxed > > > > > constraints on > > > > > the iterator's iter/sent operator- overloads, which this patch > > > > > updates. > > > > > > > > But the end() does not have the std::semiregular constraint so far as I > > > > can > > > > tell. > > > That comes from the original P/R for LWG 4166 which we proactively > > > implemented. > > > > But that resolution is *not quite right* and is not set for WP. > > testcase: > https://godbolt.org/z/Tfr4rPbc7 fixed by r16-1986
