Mutable methods in wit resources

[tqwewe]

I'm looking into using resources with the following .wit file:

resource aggregate {
  static new: function(id: string) -> aggregate
  apply-events: function(event: list<list<u8>>)
}

Which generates:

pub trait Aggregate {
    fn new(id: String,) -> wit_bindgen_rust::Handle<super::Aggregate>;
    fn apply_events(&self,event: Vec<Vec<u8>>,);
}

But using the online demo to see the generated rust code for export, the apply-events method takes &self. But what if I want to mutate self with &mut self, is this possible?

[alexcrichton]

This is currently due to the assumption that components allow for being recursively entered. This means that if Rust handed out &mut T then it would be memory unsafe to recursively call the component. This means that there's no way to use &mut self and you need to use interior mutability such as Cell<T> or RefCell<T>.

I believe the most recent iteration of the component model disallows recursively entering a component, though, so a future iteration of wit-bindgen for the updated component model will likely define all methods with &mut self since you'll have exclusive access at all times.

[tqwewe]

Oh right! Thanks for all the info.
For now I'll use Cell or RefCell, and with that update I guess I can easily modify my code to use &mut self instead.

I truly appreciate the hard work you guys are doing. Feel free to close this issue if you think it's not needed, or it can be kept open as a tracker until &mut self.

[alexcrichton]

Ok I'll leave this open so when we see this again I can confirm that this change was made or not.

[alexcrichton]

Ok I'm going to close this in favor of #201 since this is part of the new canonical ABI updates.