Re: [boost] [preprocessor] help generating create functions

From: Peder Holt (peder.holt_at_[hidden])
Date: 2005-09-14 05:22:34

On 9/14/05, Jason Hise <chaos_at_[hidden]> wrote:
> Background: I am using a few functions which have the following form:
> 
> void create (  );
> 
> template < typename P1 >
> void create ( P1 p1 );
> 
> template < typename P1, typename P2 >
> void create ( P1 p1, P2 p2 );
> [...]
> 
> I am trying to generate these using the boost preprocessor library, but
> I am getting an error.  This is probably because I do not fully
> understand how the order of expansion of function-like macros works.
> The error is:
> warning C4002: too many actual parameters for macro 'BOOST_PP_IIF_1'
> 
> My code is as follows:
> 
> #define BOOST_PP_LOCAL_LIMITS (0,
> BOOST_SINGLETON_PTR_MAX_CONSTRUCTOR_PARAMS)
> #define BOOST_PP_LOCAL_MACRO(n)                                         \
> BOOST_PP_IF(n, template < BOOST_PP_ENUM_PARAMS(n, typename P) >,        \
> BOOST_PP_EMPTY()) void create ( BOOST_PP_ENUM_BINARY_PARAMS(n,          \
>     typename ::boost::call_traits < P, >::param_type p ) )              \
> {                                                                       \
>     policy_ptr->get_creator (  )->create                                \
>         ( BOOST_PP_ENUM_PARAMS(n, p) );                                 \
> }
> #include BOOST_PP_LOCAL_ITERATE()
> 
> What am I doing wrong?

Try replacing
BOOST_PP_IF with BOOST_PP_EXPR_IF:

BOOST_PP_EXPR_IF(n, template < BOOST_PP_ENUM_PARAMS(n, typename P) >)\

If I understand it correctly,
BOOST_PP_EMPTY() expands to nothing before BOOST_PP_IF is called,
causing BOOST_PP_IF to be called with:
BOOST_PP_IF(n, template < BOOST_PP_ENUM_PARAMS(n, typename P) >,)

Regards,
Peder

> 
> -Jason
> 
> _______________________________________________
> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
>