Defining receive method for Akka actor

Question

Actors are implemented by extending the Actor base trait and implementing the receive method. The receive method should define a series of case statements (which has the type PartialFunction[Any, Unit]) that defines which messages your Actor can handle, using standard Scala pattern matching, along with the implementation of how the messages should be processed.

Code:

class MyActor extends Actor {
  val log = Logging(context.system, this)

  def receive = {
    case "test" ⇒ log.info("received test")
    case _      ⇒ log.info("received unknown message")
  }
}

There is no input to receive, so what is being matched in the case statements? Also, how does PartialFunction[Any, Unit] come into the picture here?

Leo C Leo C · Accepted Answer · 2018-05-14T00:22:09

Actors are message-driven and input is fed to an actor like messages sent to a mailbox. Messages are most commonly sent to an actor via the fire-and-forget tell (i.e. !), like:

myActor ! "test"

The receive method in an actor allows one to pattern-match the messages (generally by type) to process them accordingly. The method has type PartialFunction[Any, Unit] so that:

case pattern-matching, which is a partial function, fits well as a screening tool to effectively handle various types of incoming messages
it can take messages of any type, process them in any way necessary and doesn't need to return anything, like:
```
case i: Int => // do something with i
case s: String => // do something with s
// ...
```

Note that in the case of unhandled messages, under the hood an UnhandledMessage() will be published to the ActorSystem.

Defining receive method for Akka actor

2 Answers