Last Updated: October 28, 2018
· ajermakovics

Chaining Akka actor receive() methods

Sometimes when writing Akka actors you want to mix in traits that also handle incoming messages. The problem is that if you define Actor.receive in a trait you can no longer define it in traits.

To solve this one can define a Receiving trait that chains multiple receive functions using orElse :

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

Using this in actors with traits is easy:

trait Handler extends Receiving {
  receiver {
    case Handle => /* I'm the first to handle messages */

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

Alternative solutions available in the docs