t all cleaOn 11 January 2018 at 10:05, David Brown wrote: > Maybe it is easier to say "gcc supports <=> in C++2a, and as an > extension also supports it in C and C++ of any standard" ? I don't > believe there is any way for it to conflict with existing valid code, so > it would do no harm as a gcc extension like that - and C users can then > use it too.
It's not very useful in C because you need the comparison category types, which are classes defined in <compare> (see http://en.cppreference.com/w/cpp/header/compare) C doesn't have those types, and can't define anything close. And it's non-conforming to declare those types in pre-C++2a, because the names could be used by user programs. Potentially the types could be defined with reserved names like __strong_ordering, and then make std::strong_ordering a typedef for that, but there are also changes to the language spec that go with the new operator, and enabling those pre-C++2a could change the meaning of valid code. So it's not ar it does no harm.
