Add type-safe state

[pickfire]

Usually, the state should be well-defined ahead of time, but currently apalis uses a HashMap<TypeId, State> (simplified).

https://github.com/geofmureithi/apalis/blob/28353732e45277c21966f0265464ff57b8159ec9/packages/apalis-core/src/data.rs#L10

Axum provides an option here to use the state extractor, once globally (actually per router).

https://github.com/tokio-rs/axum/blob/c4890b844b0534f5b005342ef268b9ef620c875a/axum/src/routing/mod.rs#L726-L732

So here users could have a struct instead, and this would be resolved compile-time.

Axum does have anymap but it's for extensions, and it would be rarer for such cases such that state is not known ahead of time, using https://docs.rs/http/latest/http/struct.Extensions.html.

[geofmureithi]

I am also curious, have you actually experienced problems using Data? Have you looked at FromRequest which allows you to have compile time checked but runtime extracted state?
I do note the benefits but this would need an overhaul of the complete type system (as Apalis does not have global state). I don't think this will be a priority for v1. It can be considered in future versions if enough interest is expressed.

[geofmureithi]

Also worth looking at:

• https://docs.rs/apalis-core/1.0.0-alpha.6/apalis_core/worker/ext/index.html

Allows extending workers with something like with_state but there would need some extra work to ensure compile time correctness.

[pickfire]

I am also curious, have you actually experienced problems using Data? Have you looked at FromRequest which allows you to have compile time checked but runtime extracted state?

I don't have an issue, I looked at the code and I remembers you said it's a goal to not have any extra unnecessary global stuff, that's why I opened an issue. Feel free to close it if it's not a priority.

I noticed some of the extension traits are being done on worker level instead of the task level which I was looking for (like task level circuit breaker).