https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95322
--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:6c2582c0406250c66e2eb3651f8e8638796b7f53 commit r11-673-g6c2582c0406250c66e2eb3651f8e8638796b7f53 Author: Jonathan Wakely <jwak...@redhat.com> Date: Wed May 27 22:08:15 2020 +0100 libstdc++: Fix view adaptors for mixed-const sentinels and iterators (PR 95322) The bug report is that transform_view's sentinel<false> cannot be compared to its iterator<true>. The comparison is supposed to use operator==(iterator<Const>, sentinel<Const>) after converting sentinel<false> to sentinel<true>. However, the operator== is a hidden friend so is not a candidate when comparing iterator<true> with sentinel<false>. The required conversion would only happen if we'd found the operator, but we can't find the operator until after the conversion happens. A new LWG issue has been reported, but not yet assigned a number. The solution suggested by Casey Carter is to make the hidden friends of the sentinel types work with iterators of any const-ness, so that no conversions are required. Patrick Palka observed that join_view has a similar problem and a similar fix is used for its sentinel. PR libstdc++/95322 * include/std/ranges (transform_view::_Sentinel): Allow hidden friends to work with _Iterator<true> and _Iterator<false>. (join_view::_Sentinel): Likewise. * testsuite/std/ranges/adaptors/95322.cc: New test.
