泛型函数

def receiverStream[T: ClassTag](receiver: Receiver[T]): ReceiverInputDStream[T] = {
  withNamedScope("receiver stream") {
    new PluggableInputDStream[T](this, receiver)
  }
}

T: ClassTag 约束了类型是ClassTag

如何优雅的使用ClassTag,这篇文章可能对你有帮助:https://zhuanlan.zhihu.com/p/69792401
(我还没认真看…)