Hello all, I asked this question before but received no answer: Is there any problem in using `BOOST_PP_UNARY()` to check if a token matches a predefined keyword as indicated by the code below? The following `IS_PUBLIC(token)` macro expands to 1 if `token` is `public`, to 0 otherwise: #define PUBLIC_public (1) #define IS_PUBLIC(token) BOOST_PP_IS_UNARY(BOOST_PP_CAT(PUBLIC_, token)) IS_PUBLIC(public) // Expand to 1. IS_PUBLIC(abc) // Expand to 0. This works just fine on both GCC and MSVC. However, `BOOST_PP_UNARY()` is only part of Boost.Preprocessor private API because: Paul Mensonides mentioned in http://lists.boost.org/Archives/boost/2004/08/70238.php
Paul Mensonides wrote: I know. They (and other types of detection macros) are very useful. Right now, the Borland configuration is used by the IBM preprocessor and the Sun preprocessor also. I'd like to know whether or not those macro definitions work correctly on those preprocessors before I add it. Though those macros aren't part of the public interface, they are part of the internal interface. I.e. they are used internally as if they were a public interface (though they are used carefully on some preprocessors). They are stable, and the worst thing that might happen in the future is that they will be moved to a different directory. Thus, you can use them, but beware of VC and versions of MWCW prior to v9. They in particular have severe problems with expansion order. E.g. VC will even fail this test:
(Boost.Preprocessor, Boost.Typeof, and Boost.Spirit already use `BOOST_PP_UNARY()` internally.) Thank you very much. -- Lorenzo