scala中的self type

private[spark] trait ActorLogReceive {
  self: Actor =>

  override def receive: Actor.Receive = new Actor.Receive {

    private val _receiveWithLogging = receiveWithLogging

    override def isDefinedAt(o: Any): Boolean = {
      val handled = _receiveWithLogging.isDefinedAt(o)
      if (!handled) {
        log.debug(s"Received unexpected actor system event: $o")
      }
      handled
    }

    override def apply(o: Any): Unit = {
      if (log.isDebugEnabled) {
        log.debug(s"[actor] received message $o from ${self.sender}")
      }
      val start = System.nanoTime
      _receiveWithLogging.apply(o)
      val timeTaken = (System.nanoTime - start).toDouble / 1000000
      if (log.isDebugEnabled) {
        log.debug(s"[actor] handled message ($timeTaken ms) $o from ${self.sender}")
      }
    }
  }

  def receiveWithLogging: Actor.Receive

  protected def log: Logger
}

    lazy val actorRef = actorSystem.actorOf(Props(new Actor with ActorLogReceive with Logging{
      override def receiveWithLogging: Receive = ???
    }))