On 11 January 2018 at 11:28, David Brown wrote: > On 11/01/18 11:13, Jonathan Wakely wrote: >> 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. >> > > Surely you can get very close by simply returning an int, value -1, 0 or > 1? That is what other languages (like PHP) do for their <=> operator. > There are complications - such as for floating point when you have NaNs. > But I think you could have a very successful operator if you defined "a > <=> b" to be the same as "(a > b) - (a < b)". > > Whether it would be particularly /useful/ or not is another matter. I > was thinking mainly in terms of saving effort when making C++2a support > - rather than having to making the new operator conditional on a > particular version of the standards, it could be accepted in any version.
It seems like the wrong trade-off. We have dozens of features that depend on the standards mode, we know how to do that. Simply slamming a new language feature in all modes (*and* in a different language with a different front-end!) to save a small amount of effort doesn't seem like a good idea to me. Especially if it then doesn't even work the same pre-C++2a, as know we need to test it in additional ways.
