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

With Boost.Mp11, this is a short one-liner (as always):

using input = type_list;
using result = mp_product<
    type_pair,
    input, input>;

Demo.

---

We can generalize this to picking N things, with repetition, from that input. We can't use type_pair anymore to group our elements, so we'll just have a list of type_list of elements. To do that, we basically need to write:

mp_product
//                    ~~~~~~~ N times ~~~~~~~~

Which is also the same as:

mp_product_q, input, input, ..., input>
//                                ~~~~~~~ N times ~~~~~~~~

One way to do that is:

template 
using product = mp_apply<
    mp_product_q,
    mp_append<
        mp_list>, 
        mp_repeat_c, N>
        >>;

Demo.