return equal_to<array<T, D> >()(lhs.elts, rhs.elts);

    // This is not yet constexpr in C++17
    // return equal_to<array<T, D> >()(lhs.elts, rhs.elts);
    for (int d = 0; d < D; ++d)
      if (!equal_to<T>()(lhs.elts[d], rhs.elts[d]))
        return false;
    return true;