How to instantiate a materializer for AkkaStreams when I have a reference to the typed actor system?

Question

The code below does not compile, it says that ActorMaterializer is missing an implicit ActorRefFactory. How should I provide one?

val guardian: Behavior[Done] = Behaviors.setup(_ => {
  Behaviors.receiveMessage{
    case Done => Behaviors.stopped
  }
})
implicit val sys = ActorSystem(guardian, "sys")
implicit val materializer: Materializer = ActorMaterializer()

Answer 1

Akka Streams at this point requires a "classic" (untyped) ActorSystem which can be implicitly converted into a materializer.

So if materializing a stream inside an Akka Typed Behavior, one would

implicit val materializer = context.classicActorContext.system

And if materializing a stream outside of an actor but where you have a typed ActorSystem:

implicit val materializer = typedActorSystem.classicSystem

As mentioned by @johanandren, one can also put the Typed ActorSystem in the implicit scope, which will allow the implicit conversion to Materializer to take effect.

implicit val system = context.system