Function cartesian_power 

pub fn cartesian_power<T, const N: usize>(
    items: &[T],
) -> impl ExactSizeIterator<Item = [&T; N]> + Clone

Returns an iterator of N-length arrays containing all permutations of items (with replacement).

I.e. the Nth cartesian power of items. I.e. the cartesian product of items with itself N times.