https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111351
--- Comment #6 from Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> --- (In reply to James Y Knight from comment #5) > > Does using __builtin_is_constant_p on the union member not work? > > I've created a proof-of-concept patch for libc++ to support SSO strings > during constant evaluation. It works. > > If everyone disagrees with me and believes that this is a really awesome > foot-gun to give to users, I will go ahead and propose that patch to libc++ > maintainers. (As mentioned, that'll cause more code to be compilable under > libc++ than is possible to permit under libstdc++/MSVC implementations). FWIW #1: Personally I would be weakly in favor of that patch, but I would also be pessimistic about its chances of getting accepted in the current libc++ climate. FWIW #2: A worst-of-both-worlds option ;) would be for your patch to `if consteval` the SSO buffer size so that it would be 24 at runtime (matching libc++'s current behavior) but 16 at compile time (matching libstdc++ and Microsoft if I'm not mistaken, so you'd get your cross-vendor portability at compile time). *I* would still consider that an unnecessary-and-thus-bad crippling of libc++ string's cool 24-byte-SSO feature; but I could imagine someone else finding it more palatable than any other alternative. ["Worst-of-both-worlds" in the sense that you're paying to change the code at all, but the end result still has two codepaths that both need to be maintained, and divergence between compile-time and runtime SSO behavior.]
