C++ compile time dot product using template metaprogramming

dotprod.cpp

#include <array>
#include <cstddef>  // std::size_t

template <std::size_t N, std::size_t M = 0U>
struct dotprod {
    template <typename InputIt1, typename InputIt2, typename T>
    constexpr static T sum(InputIt1 u, InputIt2 v, T init) {
        const T uv_m{*(u + M) * T{*(v + M)}};
        return uv_m + dotprod<N, M + 1U>::sum(u, v, init);
    }
};

template <std::size_t N>
struct dotprod<N, N> {
    template <typename InputIt1, typename InputIt2, typename T>
    constexpr static T sum(InputIt1, InputIt2, T init) {
        return init;
    }
};

int main() {
    constexpr std::array u{1U, 2U, 3U};
    constexpr std::array v{4U, 5U, 6U};
    static_assert(dotprod<3U>::sum(begin(u), begin(v), 3U) == 35U);
    static_assert(dotprod<3U, 1U>::sum(begin(u), begin(v), 3U) == 31U);
    static_assert(dotprod<3U, 2U>::sum(begin(u), begin(v), 3U) == 21U);
    static_assert(dotprod<3U, 3U>::sum(begin(u), begin(v), 3U) == 3U);
}