嵌套的演员

也可以创建嵌套的 actor，即 grand-children，如下所示：

// here we pass in the ActorRefFactory explicitly as an example
val a = actor(system, "fred")(new Act {
  val b = actor("barney")(new Act {
    whenStarting { context.parent ! ("hello from " + self.path) }
  })
  become {
    case x ⇒ testActor ! x
  }
})