From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2007-06-18 07:51:56
Roman Perepelitsa wrote:
> Tobias Schwinger <tschwinger <at> isonews2.com> writes:
>
>> Yep, here's another dirty trick :
>>
>> #include <boost/preprocessor/detail/is_unary.hpp>
>>
>> #define SPECIAL (whatever)
>> #define IS_SPECIAL BOOST_PP_IS_UNARY
>>
>> IS_SPECIAL(a) // 0
>> IS_SPECIAL(b) // 0
>> IS_SPECIAL(SPECIAL) // 1
>>
>> It isn't entirely portable to older preprocessors (that's why this code
>> lives in preprocessor/detail) but should work with latest versions of
>> the widely-used compilers.
>
> This also works:
>
> #include <boost/preprocessor/facilities/is_empty.hpp>
> #include <boost/preprocessor/empty.hpp>
>
> #define SPECIAL
> #define IS_SPECIAL(x) BOOST_PP_IS_EMPTY(BOOST_PP_EMPTY() x)
>
Yep, that's even better as it allows x to be anything. Got some idea how
portable it is?
Regards,
Tobias