What's the best approach for a listener that modifies self state on event?

[pherrymason]

Hello.
I was trying to implement a hey_listen::rc::DispatcherRequest with the intention of being able to modify the internal state of the listener.
But noticed the signature of the on_event method defines self as immutable:

fn on_event(&self, event: &T) -> Option<DispatcherRequest>;

What should be a better approach of what I'm trying to achieve?
Move the state out of the listener and modify it from it?
If I'm not mistaken this would also require a mutable reference to self.

Interior mutability maybe?

struct MyStruct {
      state: RefCell<State>
}

impl Listener<Event> for MyStruct {
    fn on_event(&self, event: &Event) -> Option<DispatcherRequest> {
            self.state.replace(State::NewState);
            None
     }
}