How to create the Cartesian product of a type list?

Question

I\'d like to create the cross product of a list of types using variadic templates.

Here\'s what I have so far:

#include 
#include <         


        

Answer 1

Maybe something like this:

template  struct typelist { };

template  struct typelist_cat;

template 
struct typelist_cat, typelist>
{
    typedef typelist type;
};


template  struct product;

template 
struct product, typelist>
{
    // the cartesian product of {S} and {Ts...}
    // is a list of pairs -- here: a typelist of 2-element typelists
    typedef typelist...> S_cross_Ts;

    // the cartesian product of {Ss...} and {Ts...} (computed recursively)
    typedef typename product, typelist>::type
        Ss_cross_Ts;

    // concatenate both products
    typedef typename typelist_cat::type type;
};

// end the recursion
template 
struct product, typelist>
{
    typedef typelist<> type;
};

Now you should be able to use product, typelist>::type.