Avoid exposing internal Message type to public interface

[hirschenberger]

Hey, I have an actor with an OutputPort based subscription mechanism. But I need to spawn another thread inside to blockingly poll for a resource and notify my actor with a message, which then notifies my subscribers.

As actors can only handle one message type, is it possible to hide that internal message and not expose it along the public Subscribe message type?

[hirschenberger]

Another Question:

In Erlang/Elixir it is a common pattern to provide API functions that call or cast into the actors to make using actors look more like normal procedural code and as there's no typechecks for messages, hide the message type for error safety.

Is this also a thing for Ractor. What can be the benefit of doing so?

[slawlor]

As actors can only handle one message type, is it possible to hide that internal message and not expose it along the public Subscribe message type?

You might be able to derive something with DerivedActorRef which can use a message structure that's convertible to the actor's true message type. But without a code sample or pointer to what you're trying to do exactly, it's somewhat hard for me to say.

In Erlang/Elixir it is a common pattern to provide API functions that call or cast into the actors to make using actors look more like normal procedural code and as there's no typechecks for messages, hide the message type for error safety. Is this also a thing for Ractor. What can be the benefit of doing so?

For this part, yes it should be possible by doing the following

1. Define a custom trait which adds the methods you specifically want

trait MyMethods {
  fn send_something(&self);
}

2. Implement your trait specifically for an ActorRef<TMessage> of a given message type

impl MyMethods for ActorRef<String> {
  fn send_something(&self) {
    self.cast("Hello".to_string()).expect("Cast failed");
  }
}

or something like that ^

[hirschenberger]

As actors can only handle one message type, is it possible to hide that internal message and not expose it along the public Subscribe message type?

You might be able to derive something with DerivedActorRef which can use a message structure that's convertible to the actor's true message type. But without a code sample or pointer to what you're trying to do exactly, it's somewhat hard for me to say.

What I mean is:

For example in your filewatcher Actor, the FileWatcherMessage::Event Message is an internal message and should not be exposed to the actor's client because it's an implementation detail and may also be misused by the client which may send fake-Events to the actor.

[slawlor]

In that case you'd want to wrap that actor in another actor "parent" which exposes a subset of the messages. What you're referring to isn't directly supported unfortunately

[slawlor]

Thinking a bit more about this you could expose a DerivedActorRef with just the public API, but it can be converted into the private API

enum Public { A, B }

enum Private {A, B, C}

And if you do the conversions, you could have a DerivedActorRef hiding the private messages.

Not everything is available to this type, like you can't convert an ActorCell into this type, but it might be good enough in most cases?