How to create an Actor in Actix

#rust, #actix, #actor-model

To create an Actor in [Actix Framework], we first create a struct, then implement Actor trait for it. An actor has a Context, is where it runs, and we can control the life cycle of it via the context.

struct MyActor;

impl Actor for MyActor {
    type Context = Context<Self>;
}

The lifecycle of an actor includes these states: Started -> Running -> Stopping -> Stopped. You can work with one of the lifecycle in your Actor implementation like this:

impl Actor for MyActor {
    type Context = Context<Self>;

    fn started(&mut self, ctx: &mut Context<Self>) {
        ...
    }
}

Actors communicate with each other by exchanging messages, every message is a typed structure that implmement Message trait, and has a rtype to define its expected response type.

#[derive(Message)]
#[rtype(result = "i32")]
struct AddNumber(i32);

If you want your actor to be able to handle a certain message, implement Handler trait with that message. The implementation must describe the Result type, this is the return type that the message is expected.

impl Handler<AddNumber> for MyActor {
    type Result = i32;

    fn handle(&mut self, msg: AddNumber, ctx: &mut Self::Context) -> Self::Result {
        ...
    }
}