zip8<A, B, C, D, E, F, G, H, R>  static method 
Constructs a Stream which merges the specified Streams into a sequence using the given
zipper Function, whenever all of the provided Streams have produced
an element at a corresponding index.
Implementation
static ZipStream<dynamic, R> zip8<A, B, C, D, E, F, G, H, R>(
  Stream<A> streamA,
  Stream<B> streamB,
  Stream<C> streamC,
  Stream<D> streamD,
  Stream<E> streamE,
  Stream<F> streamF,
  Stream<G> streamG,
  Stream<H> streamH,
  R Function(A a, B b, C c, D d, E e, F f, G g, H h) zipper,
) {
  return ZipStream<dynamic, R>(
    [streamA, streamB, streamC, streamD, streamE, streamF, streamG, streamH],
    (List<dynamic> values) {
      return zipper(
        values[0] as A,
        values[1] as B,
        values[2] as C,
        values[3] as D,
        values[4] as E,
        values[5] as F,
        values[6] as G,
        values[7] as H,
      );
    },
  );
}