return r;
  }
  static constexpr CCTK_ATTRIBUTE_ALWAYS_INLINE vect iota() {
    vect r;
    for (int d = 0; d < D; ++d)
      r.elts[d] = d;

  }
  template <typename F>
  static constexpr CCTK_ATTRIBUTE_ALWAYS_INLINE vect make(const F &f) {
    return vect<int, D>::iota().map(f);