https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108543
--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> --- struct _Bit_iterator_base { long _M_p; friend bool operator<(_Bit_iterator_base __x, _Bit_iterator_base __y) { return &__x._M_p - &__y._M_p; } };