[boost] [config] defining __has_extension in suffix.hpp?

Subject: [boost] [config] defining __has_extension in suffix.hpp?
From: Peter Dimov (lists_at_[hidden])
Date: 2015-01-21 21:21:31

It's useful to have

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

#ifndef __has_extension
#define __has_extension __has_feature
#endif

in suffix.hpp so that one can then use __has_extension(foo) everywhere 
without fear. Otherwise, even

#if defined(__clang__) && defined(__has_extension) && __has_extension(foo)

is a preprocessor error when __has_extension is not defined (which it isn't 
when not on Clang.)