Re: [boost] BOOST_PP_ENUM_PARAMS can't be nested inside BOOST_PP_IF?

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2006-01-28 10:38:03

Arkadiy Vertleyb wrote:
> Hi,
> 
> The following code:
> 
> #include <boost/preprocessor/control/if.hpp>
> #include <boost/preprocessor/enum_params.hpp>
> BOOST_PP_ENUM_PARAMS(3, p)
> BOOST_PP_IF(1, BOOST_PP_ENUM_PARAMS(3, p), blah)
> 
> results in the following text (vc71, main CVS):
> 
> p0 , p1 , p2
> p0
> 
> and a warning:
> 
> to many parameters for BOOST_PP_IIF_1.
> 
> What's wrong?

"Being lazy" solves the problem:

  #include <boost/preprocessor/control/if.hpp>
  #include <boost/preprocessor/enum_params.hpp>
  #include <boost/preprocessor/tuple/eat.hpp>

  BOOST_PP_ENUM_PARAMS(3, p)
  BOOST_PP_IF(1, BOOST_PP_ENUM_PARAMS, blah BOOST_PP_TUPLE_EAT(2))(3,p)

Note: 
- BOOST_PP_IF does not get disabled  
- lazy invocation => no repetition in the "else-case".

Regards,

Tobias