Chapter 12

1. Encapsulation with Actors—mutable state is only accessible from one actor, one thread. Actors are organized in hierarchies, and parents supervise children to achieve fault tolerance.
2. We do so by extending the Actor class and implementing the receive method.
3. We do so by calling the actorOf method on ActorSystem or ActorContext.
4. Using the ! operator on an ActorRef—targetActor ! message.
5. The ! operator implements a fire-and-forget type of message sending. It sends a message and returns immediately. Ask pattern involves sending a message using ? operator instead, which returns a Future[Any] which will complete once the target actor responds—val futureMessage: Future[Any] = targetActor ? message.
6. The Pipe pattern instructs a Future to send a message to an actor upon completion of the Future's computation—future pipeTo targetActor.