Re: [Boost-users] [preprocessor] Argument list conversion

18 Jun 2007


      Server Levent Yilmaz wrote:
...
On 6/18/07, *Tobias Schwinger* mailto:tschwinger@isonews2.com> wrote:
Roman Perepelitsa wrote:
     > Tobias Schwinger http://isonews2.com> writes:
     >
     >> Yep, here's another dirty trick :
     >>
     >>      #include 
     >>
     >>      #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 
     > #include 
     >
     > #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?
Well, IS_UNARY trick also works for pretty much anything except maybe 
another non-SPECIAL unary.
Or a non-SPECIAL non-unary tuple, e.g. (foo,bar).
...
What exactly is the offending code in BOOST_PP_IS_UNARY that makes it 
non-portable?
IIRC, there is no offending code - just some deficient preprocessor 
implementations around that can't handle it...


Regards,
Tobias