https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101937
--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to Jonathan Wakely from comment #6) > The problem is that ctx._M_indent is a member access expression through a > reference, which is not allowed in constant expressions. This is a silly > restriction that https://wg21.link/p2280r2 aims to change. Just FYI the GCC bug accepting this code is PR 72756.
