Callback pattern in rust.

callback.rs

use std::boxed::Box;

type Callback = Box<dyn Fn(&mut f64, &f64)>;
type Condition = Box<dyn Fn(&f64, &f64) -> bool>;
type Effect = Box<dyn Fn(&mut f64, &f64)>;

fn step(u: &mut f64, t: &mut f64, callback: &Callback) {
    callback(u, t);
    *t += 1.;
    *u += 1.;
}

fn make_callback(condition: Condition, effect: Effect) -> Callback {
    let cb = move |u: &mut f64, t: &f64| {
        if condition(u, t) {
            effect(u, t)
        }
    };
    Box::new(cb)
}

fn main() {
    let u = &mut 0.;
    let t = &mut 0.;

    let condition: Condition = Box::new(|u: &f64, t: &f64| *u >= 3.);
    let effect: Effect = Box::new(|u: &mut f64, t: &f64| *u = 1.);

    let cb = make_callback(condition, effect);

    for i in 1..9 {
        step(u, t, &cb);
        println!("u: {0}, t: {1}", u, t);
    }
}