https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88595
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- This part of the error is no longer produced in GCC 10+: b.cc: In constructor ‘constexpr Container::Container(int)’: b.cc:12:44: error: member ‘Container::car’ must be initialized by mem-initializer in ‘constexpr’ constructor constexpr Container (int car) :car(car) {} ^