Why would that be a problem in rust?
To do this in Rust, the closure needs a mutable reference to the button. However, the GUI event loop also needs a reference to the button to draw it on the screen. In Rust, you can have many immutable references, __or__ exactly one mutable reference, but never both at the same time. Since the GUI framework holds the button, it won't let your closure mutably borrow it at the same time.
use std::rc::Rc;
use std::cell::RefCell;
struct Button {
text: String,
on_click: Option<Rc<dyn Fn()>>,
}
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<RefCell<Button>>) {
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!"]Many interactive programs can be GetInput(); ChangeState(); DrawState();
Why wouldn't their lifetimes be isolated?
Also the drawing doesn't need a mutable reference.