scala - 如何与 Akka Actor 一起使用可堆叠特征模式？

Question

我正在尝试实现一个 Pub/Sub 特征，以使用可堆叠特征混合到其他 akka actor 中。

这是我的想法:

trait PubSubActor extends Actor {
  abstract override def receive = 
    super.receive orElse {
      case Subscribe(topic) => /* ... */
      case Publish(topic, msg) => /* ... */
    }
}

class MyActor extends Actor with PubSubActor {
  override def receive = {
    case SomeMessage(a, b, c) => /* ... */
  }
}

此时，编译器会抛出一个错误: 错误:在特征 MyActor 中重写方法接收...方法接收需要“抽象重写”修饰符。

你能向我解释一下为什么这不起作用吗？我该如何修复它才能正常工作？

谢谢!

更新

以下作品:

trait PubSubActor extends Actor {
  abstract override def receive = 
    super.receive orElse {
      case Subscribe(topic) => /* ... */
      case Publish(topic, msg) => /* ... */
    }
}

class MyActor extends Actor {
  override def receive = {
    case SomeMessage(a, b, c) => /* ... */
  }
}

class MyActorImpl extends MyActor with PubSubActor

但是为什么呢？为什么我可以通过这种方式获得我想要的行为，而不能通过其他方式获得？有什么理由吗？我似乎无法弄清楚这两个样本之间造成差异的根本区别。

Answer 1

有一个简单而简洁的解决方案:

使用 orElse 定义链接多个接收函数的接收特征:

trait Receiving { 
  var receivers: Receive = Actor.emptyBehavior 
  def receiver(next: Actor.Receive) { receivers = receivers orElse next }
  def receive = receivers // Actor.receive definition
}

在 Actor 中使用它很容易:

trait PubSubActor extends Receiving {
  receiver {
    case Publish => /* I'm the first to handle messages */
  }
}

class MyActor extends PubSubActor with Receiving {
  receiver {
    case SomeMessage => /* PubSubActor didn't handle, I receive the message */ 
  }
}

第一个 PubSubActor 的接收将被调用。如果消息未被处理，它将被传递到 MyActor 的接收。