is there any way to create custom Actor traits that are object safe ?

[cameronbraid]

I would like to define a custom actor trait like the following :

pub trait StorageActor : Handler<WriteData> + Handler<ReadData> {}

However when trying to use a LocalActorRef<StorageActor> I get

size for values of type `(dyn StorageActor + 'static)` cannot be known at compilation time
the trait `Sized` is not implemented for `(dyn StorageActor + 'static)`

I'm still fairly new to rust, and after reading https://huonw.github.io/blog/2015/01/object-safety/ I still don't fully understand what the specific blocker is. - could it be in the Actor trait fn actor_ref(&self, ctx: &ActorContext) -> LocalActorRef<Self> which seems to match up to the link under References Self - There’s two fundamental ways in which this can happen, as an argument or as a return value

Cheers

Cameron

[LeonHartley]

Hey @cameronbraid,

It's not currently possible to use a trait object in place of an Actor type for LocalActorRefs, there is too much reliance on using the type directly, with requirements for it to be Sized. I do think it's possible to remove this limitation in the future, but will require a little more thought.

As a workaround, you could potentially create a Storage trait, which has async read and write methods, and implementations of it calling some underlying LocalActorRef respectively - this is a pattern that I've used myself in Coerce, when writing the actor persistence storage system with support for multiple backends: https://github.com/LeonHartley/Coerce-rs/blob/master/coerce/src/persistent/journal/storage.rs#L14

Implementation example, backed by an actor: https://github.com/LeonHartley/Coerce-rs/blob/master/providers/persistence/coerce-redis/src/journal/mod.rs#L125