fn do_it(initial_state: i32) -> (Box<Fn() -> i32>, Box<FnMut(&str)>) {
    let mut internal_state = initial_state;

    let get_state = Box::new(move || internal_state);

    let update = Box::new(|input: &str| internal_state = input.len() as i32);

    (get_state, update)
}

fn main() {
    let (get_state, mut update) = do_it(0);
    println!("{}", get_state());
    update("hello");
    println!("{}", get_state());
}