From: Toon Knapen (toon.knapen_at_[hidden])
Date: 2004-09-03 00:22:27
Daniel James wrote:
> Well, it's almost worked, but those BOOST_PP_TUPLE_EAT_2's should expand
> to nothing. I guess it needs another expansion. The following might
> work. Please can you try it out?
results in attachment.
>
> In practice these macros will only get called from the other boost
> macros which might cause these macros to expand fully? Paul will
> understand this a lot better than me.
>
> #include <boost/preprocessor/detail/split.hpp>
> #include <boost/preprocessor/punctuation/comma.hpp>
> #include <boost/preprocessor/punctuation/paren.hpp>
> #include <boost/preprocessor/tuple/eat.hpp>
>
> #define IS_NULLARY(x) \
> IS_NULLARY_2(BOOST_PP_SPLIT(1, IS_NULLARY_C x BOOST_PP_COMMA() 0)) \
> /**/
> #define IS_NULLARY_2(x) x
> #define IS_NULLARY_C() \
> ~, 1 BOOST_PP_RPAREN() \
> BOOST_PP_TUPLE_EAT(2) BOOST_PP_LPAREN() ~ \
> /**/
>
> IS_NULLARY(()) // 1
> IS_NULLARY(()abc) // 1
> IS_NULLARY(+) // 0
> IS_NULLARY(xyz) // 0
>
> #define IS_UNARY(x) IS_NULLARY(IS_UNARY_C x)
> #define IS_UNARY_C(a) ()
>
> IS_UNARY((a)) // 1
> IS_UNARY((a)abc) // 1
> IS_UNARY(+) // 0
> IS_UNARY(xyz) // 0
>
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#line 15 "pp.cpp"
1 BOOST_PP_TUPLE_EAT_2 ( ~ , 0)
1 BOOST_PP_TUPLE_EAT_2 ( ~abc , 0)
0
0
#line 23
1 BOOST_PP_TUPLE_EAT_2 ( ~ , 0)
1 BOOST_PP_TUPLE_EAT_2 ( ~abc , 0)
0
0