Using Props.create with arguments that are injected

[steven richardson]

I am running into an issue using Props.create when providing a class and its arguments. The example below is contrived but will hopefully serve its purpose.

trait Provider {}


class DefaultProvider extends Provider {}

class MyActor(provider: Provider) extends Actor {
  def receive = ...
}

Then let's say I am injecting the provider using Guice or another container:

class ProviderPropsFactory @Inject()(protected val provider: Provider) {
  def buildProps: Props = Props.create(classOf[MyActor], provider)
}

At runtime if I try to start an actor using these props as shown here, I get an IllegalArgumentException when Akka attempts to find the matching constructor for the actor since it is only seems to match on the concrete type rather than allowing a compatible trait or an abstract type from the instance's hierarchy. 

system.actorOf(factory.buildProps)
java.lang.IllegalArgumentException: no matching constructor found on class com.sample.MyActor for arguments [class com.sample.DefaultProvider]
 at akka.util.Reflect$.error$1(Reflect.scala:82) ~[akka-actor_2.11-2.3-bin-rp-15v01p06.jar:na]
 at akka.util.Reflect$.findConstructor(Reflect.scala:106) ~[akka-actor_2.11-2.3-bin-rp-15v01p06.jar:na]
 at akka.actor.ArgsReflectConstructor.<init>(Props.scala:353) ~[akka-actor_2.11-2.3-bin-rp-15v01p06.jar:na]
 at akka.actor.IndirectActorProducer$.apply(Props.scala:312) ~[akka-actor_2.11-2.3-bin-rp-15v01p06.jar:na]
 at akka.actor.Props.producer(Props.scala:179) ~[akka-actor_2.11-2.3-bin-rp-15v01p06.jar:na]
 at akka.actor.Props.<init>(Props.scala:192) ~[akka-actor_2.11-2.3-bin-rp-15v01p06.jar:na]
 at akka.actor.Props$.create(Props.scala:99) ~[akka-actor_2.11-2.3-bin-rp-15v01p06.jar:na]

I could use this snippet  below instead which I know would work, but this type of approach is discouraged/deprecated and I would like to be doing things the recommended way. Do you have any suggestions?

class ProviderPropsFactory @Inject()(protected val provider: Provider) {
  def buildProps: Props = Props(new MyActor(provider))
}

Any and all help is appreciated.

Thanks,

Steve

[Heiko Seeberger]

Why do you think that the `Props` factory taking the actor constructor by name is discouraged? It’s the opposite: You definitely SHOULD use it, the other approach is using reflection at runtime and is not refactoring safe.

Cheers

Heiko

--

Heiko Seeberger

Home: heikoseeberger.de

Twitter: @hseeberger

Public key: keybase.io/hseeberger

--
>>>>>>>>>> Read the docs: http://akka.io/docs/
>>>>>>>>>> Check the FAQ: http://doc.akka.io/docs/akka/current/additional/faq.html
>>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user
---
You received this message because you are subscribed to the Google Groups "Akka User List" group.
To unsubscribe from this group and stop receiving emails from it, send an email to akka-user+...@googlegroups.com.
To post to this group, send email to akka...@googlegroups.com.
Visit this group at https://groups.google.com/group/akka-user.
For more options, visit https://groups.google.com/d/optout.

[sti...@intelli-vision.com]

I agree to use constructor by name approach. But what's wrong with classOf approach?
I have upgraded microservice from play 2.4 to play 2.5 and observed same issue. I fixed 1st error bu using constructor by name approach, but later another same issue observed. As this error pops runtime, there is no way to be sure if migration is successful. Only option I have is to replace all the classOf occurrences  with constructor by name.