[cfe-dev] magic __has_feature macro

[Chris Lattner]

On Jun 12, 2009, at 6:18 PM, Eli Friedman wrote:

> On Fri, Jun 12, 2009 at 6:03 PM, Chris Lattner<clattner at apple.com>  
> wrote:
>> Hi All,
>>
>> As Clang "grows up", it will continue to get more features.  I'd like
>> to add new "__has_feature" builtin function-like macro that evaluates
>> to 0 or 1 if clang has a specified feature.
>
> What does it evaluate to if clang doesn't have the specified  
> feature? :)

haha. :)

> Sounds like a good idea.

Ok, my proposed use of if defined won't work because of the parsing  
structure of pp conditionals.  However, something like this will work:

#ifndef __has_feature
#define __has_feature(x) 0
#endif

// ...

#if __has_feature(x)
  ... whatever ...
#endif


I also plan to add a __has_builtin(x) as well, so that we can write  
things like:

#if __has_builtin(__builtin_trap)
   __builtin_trap();
#else
   abort();
#endif

Look, no autoconf, and no fragile compiler version checks! :)

I'll start working on this.

-Chris