Hi, Chris Lattner <clatt...@apple.com> skribis:
> On Jan 31, 2012, at 5:15 AM, Ludovic Courtès wrote: > >>> >>> Interestingly enough: >>> $ cat q.c >>> __has_builtin >>> $ clang -E q.c >>> <segfault> >> >> Yes, that’s what I was asking. >> >> It makes me think that the old CPP predicates (info "(gcc) Obsolete >> Features") would be more appropriate than compiler magic, with the >> caveat that they’re presumably not widely supported. > > They are similar in spirit. The major difference between the two is that it > is easy for __has_feature and friends gracefully degrade when a compiler > doesn't support them, because you can do: > > #ifndef __has_builtin > #define __has_builtin(x) 0 > #endif > > in your code, but you can't do anything like this for #assertion. That and > assertions don't have any coverage over the features that you're interested > in, and the grammar doesn't have a good way to handle multiple cases like > features/attributes/extensions/etc. Rather than assertions, one could use predicates: #if #has_builtin(foo) && #has_attribute(bar) ... #endif The difference being that (1) predicates were designed specifically for this purpose, and (2) there’s no magic involved. Thanks, Ludo’.
