Overriding capsules via dynamic dispatch (capsule providing another capsule)

[busslina]

Is it possible to override a capsule like it is in Dart?

In order to be able to provide a project capsule that has to be used at lib level.

[GregoryConrad]

Yea, you just have to use the state side effect. The syntax may be a bit tricky to arrive at though, since you'd have to return Box<dyn Capsule<Data=FooBar>> (or something like that) or a custom-made enum to support the different capsules you're switching between.

[GregoryConrad]

We don't want to compare both values on eq?

Unfortunately you can't without some other tricks because Eq itself is not object safe. You might even need a new type to support it; I am not sure right now (I'd have to try it and find out)

I suppose you are thinking on integrate this workaround on the API, maybe after doing some lifting to the code. I'm gonna test it now

Wasn't originally planning on it since I'd want to version this addition differently than the main ReArch crate. But that's solvable by just releasing another crate, so yea, I think I can clean this up and put it into a new crate. You can check back in a few days and see if I've done it by then 😉

[busslina]

Cool, thanks again.

[busslina]

BTW, I don't understand why Capsule cannot be used as object trait but DynCapsule yes. Even Chat GPT 4 said to me that both are similar in those terms.

[GregoryConrad]

The compiler should tell you why I'd imagine, but it's because:

• key() returns an impl Trait
• eq() doesn't use &self (I think that is what prevents it anyways)

Both of which prevent vtable construction. See https://doc.rust-lang.org/reference/items/traits.html#object-safety

[busslina]

hehe I get brain stack overflow trying to understand the compiler messages

[GregoryConrad]

There is now a side effect that supports this use case in rearch-effects; check out the overridable_capsule effect!

https://docs.rs/rearch-effects/latest/rearch_effects/fn.overridable_capsule.html