use std::rc::Rc;
    use std::cell::RefCell;
    
    struct Button {
        text: String,
        on_click: Option>,
    }
    
    impl Button {
        fn new(text: &str) -> Self {
            Button { text: text.to_string(), on_click: None }
        }
        fn draw(&self) { println!("[Button: \"{}\"]", self.text); }
        fn fire_click(button: &Rc>) {
            let cb = button.borrow().on_click.clone();
            if let Some(cb) = cb {
                cb();
            }
        }
    }
    
    fn main() {
        let button = Rc::new(RefCell::new(Button::new("Click me")));
        let cb_handle = Rc::clone(&button);
    
        button.borrow_mut().on_click = Some(Rc::new(move || {
            cb_handle.borrow_mut().text = "Clicked!".to_string();
        }));
    
        button.borrow().draw();
        Button::fire_click(&button);
        button.borrow().draw();
    }

  [Button: "Click me"]
  [Button: "Clicked!"]