I have a small game app using trait object to handle key events and modify app state:

pub trait GameScene {
    fn handle_key_events(&self, app: &mut TypingApp, key_event: KeyEvent) -> Result<()>;
}

pub struct StartupScene {}

impl GameScene for StartupScene {
    fn handle_key_events(&self, app: &mut TypingApp, key_event: KeyEvent) -> Result<()> {
        todo!()
    }
}

pub struct TypingApp {
    /// lots of other members here
    /// ......
    /// modify above members according to the user's input
    pub cur_scene: Box<dyn GameScene>
}

impl Default for TypingApp {
    fn default() -> Self {
        Self {
            cur_scene: Box::new(StartupScene{})
        }
    }
}

impl TypingApp {
    pub fn handle_key_events(&mut self, key_event: KeyEvent) -> Result<()> {
        self.cur_scene.handle_key_events(self, key_event)
    }
}

This cannot be compiled because the last handle_key_events function:

error[E0502]: cannot borrow `*self` as mutable because it is also borrowed as immutable
  --> src/app.rs:53:9
   |
53 |         self.cur_scene.handle_key_events(self, key_event)
   |         --------------^-----------------^^^^^^^^^^^^^^^^^
   |         |              |
   |         |              immutable borrow later used by call
   |         mutable borrow occurs here
   |         immutable borrow occurs here

I just want to use GameScene object to modify members of TypingApp, how can I fix this compile error? Thanks!