Re: [Boost-users] Automate call with n template parameters

Thanks! Jeremy Pack wrote:

Hi Kevin!

On Mon, Jul 21, 2008 at 9:03 PM, Kevin Jenkins mailto:gameprogrammer@rakkar.org> wrote:

...

Is there any way to automate this, to support from 0 to n parameters?

template bool DoIt(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5) {

Boost.Preprocessor would do that.

Create two files, which I'll call:

main.hpp implementation.hpp

In main.hpp:

#include #include

#define NUM_FUNCTION_PARAMS 8 // Or however many you need.

// Define the function for 1 to 8 arguments. #define BOOST_PP_ITERATION_LIMITS(1, NUM_FUNCTION_PARAMS); #define BOOST_PP_FILENAME_1 "implementation.hpp" #include BOOST_PP_ITERATE()

And then in implementation.hpp:

// Note: If you want to support 0 arguments, you'll need to use BOOST_PP_IF // to only optionally include the template declaration. I'd recommend just putting the // argless version into main.hpp, unless the function is quite complex. template inline void MyFunc(BOST_PP_ENUM_BINARY_PARAMS(N, Param, p)) { #define DO_THAT(n) DoThat(BOOST_PP_CAT(p, n)); BOOST_PP_REPEAT(N, DO_THAT,) #undef DO_THAT }

Hope that helps - and can't promise it will immediately compile!

I do this in the proposed Extension and Reflection libraries a few times. The best example is probably in the adaptable_factory class, where I wanted to support calling a factory function without knowing its arguments:

http://svn.boost.org/trac/boost/browser/sandbox/boost/extension/impl/adaptab... http://svn.boost.org/trac/boost/browser/sandbox/boost/extension/adaptable_fa...

Let me know if you have problems getting your function to compile. Also, with Boost.Preprocessor, "gcc -E" is your best friend.

Good luck!

Jeremy Pack http://boost-extension.blogspot.com /boost-users