Pass an actor as parameter

Question

For example, I have

trait Logger { 
  def log(m: Message) = ??? 
}

If I want to pass a Logger as parameter I would simple call def foo(l: Logger).

But if I have

trait Logger { 
  def log(m: Message) = ??? 
  def receive = {
    case m: Message = log(m)
  }
}

,I must pass an ActorRef to be able to call !/? etc on it. But that completely breaks type safety - def log(ar: ActorRef), and nothing says that it should be an Logger underneath.

So, in the end I'd like to call

class Foo(logger: Logger) {
  def foo(m: Message) = logger ! message
}

score 4 · Accepted Answer · answered Dec 27 '15 at 17:32

Well, yes. That's just how Akka works, because actors can change behavior. See How to restrict actor messages to specific types?.

Solution 1: define a wrapper class like

case class LoggerActor(ar: ActorRef) {
  def log(m: Message) = ar ! m
}

And then use LoggerActor where you want to make sure you have a Logger. Of course, if you want to do it everywhere, you'll probably want to automate creation of these classes somehow.

Solution 2: Use Akka Typed. Note it's experimental. I won't copy the documentation from there.

Solution 3: Use Scalaz actors instead, which were typed from the beginning. See https://github.com/scalaz/scalaz/blob/series/7.3.x/tests/src/test/scala/scalaz/concurrent/ActorTest.scala for usage examples. For your case it could be

val logger = new Logger { ... }
val loggerActor = new Actor[Message](logger.log)

score -1 · Answer 2 · answered Dec 27 '15 at 16:32

-1

You can specify that your ActorRef should implement Logger too:

def log(ar: ActorRef with Logger)

answered Dec 27 '15 at 16:32

jopasserat

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I'm still not sure to understand your porblem... Can't you apply the same thing I state in my answer to this logger that comes as a parameter to your class Foo? `class Foo(logger: ActorRef with Logger)`?? – jopasserat Dec 27 '15 at 17:12
Then `logger: ActorRef with Logger` would get method `log`, but it won't use `Logger`'s `receive`. So `logger ! message` would do nothing. – dveim Dec 27 '15 at 17:16
This answer will not work. User code never extends `ActorRef`. – Ryan Dec 28 '15 at 02:18
was suggesting for him to do so. but the wrapper or Scalaz version looks better – jopasserat Dec 28 '15 at 11:59
There's no way to extend `ActorRef` in a way that makes sense. – Ryan Dec 28 '15 at 17:09

Pass an actor as parameter

2 Answers2