Original Post
Okay, I'm having a little bit of trouble with template parameters. Take a little looksee, focusing mostly on the CFuntionWrapper template params My trouble is that I can't figure out how I'm going to be able to pass in the number 'N'. I'm not looking to do that at runtime, I'm sure that it needs to be done at compile time, and that's fine, no problem there. I just can't figure out how I'm going to be able to do it.
/* Use boost pre-processor stuff to generate the elements of an array, because we'll only know
at compile time how many params are needed. This is because I'm using boost::function which uses
templates and it's easier to work like this than just put in 30 template parameters, most of which
will end up as nothing.
When the macro "WRITE_ARR_ELEMENTS" is called, depending on the input it will print
array elements. Eg. an input of (4,vertex) will expand to
"vertex[0] , vertex[1] , vertex[2] , vertex[3]" during the preprocessor stage.
*/
#define WRITE_ELEMENT(z, n, arr) BOOST_PP_COMMA_IF(n) BOOST_PP_CAT(arr[, BOOST_PP_CAT(n, ]))
#define WRITE_ARR_ELEMENTS(n, input) BOOST_PP_REPEAT(n, WRITE_ELEMENT, input )
/**
* Concrete class for the function wrapper.
* NOTE:: the "BOOST_PP_ENUM_PARAMS(N, T)" preprocessor macro will insert T0, T1, T2, etc, up to the
* limit 'N', using the preprocessor ## to stick stuff together.
*/
template < BOOST_PP_ENUM_PARAMS(N, class T) >
class CFunctionWrapper : public IFunctionWrapper
{
private:
/** Boost function wrapper
* Note: to use the <T0,T1,T2,T3> we need to use boost::function2.
* If we want to use the < int (float i, char c) > form, we need boost::function
*/
boost::function2< BOOST_PP_ENUM_PARAMS(N, T) > m_function;
public:
/**
* Call the function.
* \param s A reference to a std::string object to store in any error messages
* caused when calling the function
* \param input A const reference to a util::array<boost::variant> object to store the input arguments.
* \param output A reference to a variant that will store the return value.
* \return 'true' if the call was successful, else 'false'
*/
bool call( std::string& s,
const echo::util::array< console_variant_type >& input,
console_variant_type& output )
{
// not enough function arguments
if( input.getSize() != N ){
s = "Error: not enough function arguments."; // assign error message
return false; // return error
}
// call the function
output = m_function( WRITE_ARR_ELEMENTS(N, input) );
return true;
}
};
