Store generic ActorRef

[rubengrim]

I'm trying to store an ActorRef of a generic actor that implements a specific message, but can't get it to work. Been reading through some of the source code and tried something like this:

#[derive(Actor)]
pub struct SomeActor<A>
where
    A: Actor + Message<SomeMessage>,
    ActorRef<A>: Request<A, SomeMessage, A::Mailbox>,
{
    other_actor: ActorRef<A>,
}

// Send SomeMessage like this later
self.other_actor.ask(SomeMessage).send().await;

But I get this error when sending:
no method named `send` found for struct `AskRequest<A, <A as Actor>::Mailbox, ReadyForNext, WithoutRequestTimeout, WithoutRequestTimeout>` in the current scope

The PubSub implementation seems to use a wrapper trait for the subscribers and I'm thinking that I might need to do something similar, but I honestly don't understand it. Any help in the right direction is appreciated!

[tqwewe]

Hi rubengrim, this is perfect timing for something I've been working on today actually! I just saw this question are creating a PR with my rework of how sending is done. #39

With these new changes, all you should need are the following bounds for ask requests:

kameo/src/request/ask.rs

Lines 166 to 169 in ad1984a

	where
	A: Actor<Mailbox = $mailbox<A>> + Message<M>,
	M: Send + 'static,
	{

In your case, since you're directly using SomeMessage, you would just need:

#[derive(Actor)]
pub struct SomeActor<A>
where
    A: Actor<Mailbox = BoundedMailbox<A>> + Message<SomeMessage>,
{
    other_actor: ActorRef<A>,
}

However, this approach requires the mailbox to be known. If you want a super generic approach, you could do something like this:

#[derive(Actor)]
struct SomeActor<A, Tm, Tr>
where
    A: Actor + Message<SomeMessage>,
    AskRequest<
        LocalAskRequest<A, A::Mailbox>,
        A::Mailbox,
        SomeMessage,
        Tm,
        Tr,
    >: MessageSend,
{
    other_actor: ActorRef<A>,
}

Tm and Tr here are generics for whether the ask request has a mailbox timeout or reply timeout set.
Eg:

actor_ref.ask(...).mailbox_timeout(...).reply_timeout(...).send().await

If you know there will or will not be timeouts used here, you can hard code them to be WithRequestTimeout or WithoutRequestTimeout.

An alternative to above with no timeouts available:

#[derive(Actor)]
struct SomeActor<A>
where
    A: Actor + Message<SomeMessage>,
    AskRequest<
        LocalAskRequest<A, A::Mailbox>,
        A::Mailbox,
        SomeMessage,
        WithoutRequestTimeout,
        WithoutRequestTimeout,
    >: MessageSend,
{
    other_actor: ActorRef<A>,
}

It's quite verbose, but is pretty powerful for allowing different ways of sending messages based on mailbox type, or if there's timeouts used.

[rubengrim]

Yeah that's great timing! Mailbox/timeout will be known so the first example will work great. Thank you for the help and nice work on the crate, really enjoying using it!

[tqwewe]

Very cool of you to be looking into the source code :)

I have realised that your requirements aren't really dependant on the new PR I mentioned. I believe all you needed was to specify the mailbox there too. A: Actor<Mailbox = BoundedMailbox<A>> + Message<SomeMessage>

The bounds required based on the current version of kameo are here:

kameo/src/request/ask.rs

Lines 374 to 389 in 6f7b6f7

	impl<A, M>
	AskRequest<
	LocalAskRequest<A, BoundedMailbox<A>>,
	BoundedMailbox<A>,
	M,
	WithoutRequestTimeout,
	WithoutRequestTimeout,
	>
	where
	A: Actor<Mailbox = BoundedMailbox<A>> + Message<M>,
	M: 'static,
	{
	/// Sends the message, waiting for a reply.
	pub async fn send(
	self,
	) -> Result<<A::Reply as Reply>::Ok, SendError<M, <A::Reply as Reply>::Error>> {

[rubengrim]

Works perfectly, thanks again!

[tqwewe]

Just posting an update to this, with the PR #71, this issue should never come up anymore, as most request types work regardless of the actors mailbox.