passing comma to preprocessor

[Christof Warlich]

Hi,

I need to use boost's BOOST_PP_IF(condition, then, else) macro, with "condition" being evaluated
from a template, e.g. is_convertible<typename A, typename B>.

Thus, with two classes A and B, I'd like to write:

BOOST_PP_IF(is_convertible<A, B>::value, std::cout << "if\n", std::cout << "else\n");

Unfortunately, the preprocessor complains because it sees 4 parameters instead of 3 due to the comma
between the template parameters.

To make my question independent from boost, having a macro like

#define M(x) x

how do I pass something like

someTemplate<x, y> to M(x)?

Thanks for any ideas,

Christof

P.S.: I already tried boost's BOOST_PP_COMMA() macro, but this did not solve the problem.

 

[Micah Cowan]

BOOST_PP_IF(is_convertible<A, B>::value, std::cout << "if\n", std::cout << "else\n");

Try:

BOOST_PP_IF((is_convertible<A, B>::value), std::cout << "if\n", std::cout << "else\n");

 

[Christof Warlich]

Try:

BOOST_PP_IF((is_convertible<A, B>::value), std::cout << "if\n", std::cout << "else\n");

Oh, yeah, thanks, this is it. But anyway, I misinterpreted BOOST_PP_IF
to be a macro wrapper for some template "if" implementation, which it
doesn't seem to be. Instead, it looks like just being some preprocessor
code, so my construct would not have worked even without my comma-problem.