https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109863
--- Comment #2 from Xi Ruoyao <xry111 at gcc dot gnu.org> --- (In reply to Xi Ruoyao from comment #1) > Note that the entire "initializing a flexible array member" thing is a GNU > extension and not supported by the standard. So GCC is free to support the > constexpr case but reject other non-static cases. Or, "it's an extension after all, so it's not related to if the standard say constexpr implies static or not".