https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116342
--- Comment #4 from Zhao Dai <daidodo at gmail dot com> --- > floating point is a fundamental types so there is no ADL involved ... Thanks for pointing out! I checked other types (int/bool/nullptr_t/type alias/...), and it seems all builtin types and their alias are excluded by ADL thus cannot have customised weak/strong_order. > IIUC GCC and libstdc++ are doing the right thing - you're just not allowed to > customize comparison for float. I don't know if C++ Standard says `strong/weak_order` are customisable only for user-defined types. If yes, I'm happy to know. Otherwise, since libstdc++ is customising float comparison with assumptions, e.g -NaN < -INF < 0 < +INF < +NaN, it sounds like a defect to me if libstdc++ doesn't allow any other assumptions and use cases. Another angle is the original intention of partial/weak/strong_order customisation points. My understanding is that they "promote" order categories when needed, like from partial_ordering to weak/strong_ordering for floating point types. If it's one of the intentions, I don't see why builtin types and their alias should be excluded.
