Akka Streams -如何生成列表的大小，然后是整个列表

import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import akka.stream.scaladsl._

object ListSizeExample extends App {
  implicit val system = ActorSystem("ListSizeExample")
  implicit val materializer = ActorMaterializer()

  val list = List(1, 2, 3, 4, 5)

  val source = Source(list)
  val sizeFlow = Flow[Int].fold(0)((acc, _) => acc + 1)
  val sink = Sink.head[Int]

  val listSizeFuture = source.via(sizeFlow).runWith(sink)

  listSizeFuture.foreach { size =>
    println(s"List size: $size")
    system.terminate()
  }
}