How to zip vectors using template metaprogramming

Question

I am practicing on template meta-programming and wanted to implement a simple trivial meta-function. I wonder how one can implement zip functionality on custom vectors. What I have in my mind is as follows:

Here is how the zip operation for this custom vector look like:

Inputs:

Vector<1, 2, 3>
Vector<2, 3, 4>
Vector<3, 4, 5>

Output:

Vector<6, 24, 60>

I believe my Vector class should be declared like:

template<int... vals>
struct Vector;

zip meta-function should have the signature:

template<typename... Vectors>
struct zip
{
    ///
}

I cannot figure out how to multiply values in the input vectors that happen to be in the same index via template meta-programming?

Answer 1

You can partially specialise zip in order to expose the template parameters of the Vectors you pass.

template<typename...>
struct zip;

template<int... Us, int... Vs, typename... Tail>
struct zip<Vector<Us...>, Vector<Vs...>, Tail...> {
    using type = typename zip<Vector<(Us * Vs)...>, Tail...>::type;
};

template<typename T>
struct zip<T> {
    using type = T;
};

static_assert(std::is_same<zip<Vector<2, 4, 6>, 
                               Vector<1, 2, 3>, 
                               Vector<3, 6, 9>>::type, 
                               /* == */ Vector<6, 48, 162>>::value);