asclosure.rs

fn main() {
    let make_counter = || {
        let mut count = 0;
        move || { let so_far = count; count += 1; so_far }
    };
    let mut a = make_counter();
    let mut b = make_counter();
    println!("{} {}", a(), a());
    println!("{} {}", b(), b());
}

asfunctionnow.rs

fn make_counter() -> Box<FnMut()->i32> {
    let mut count = 0;
    Box::new(move || { let so_far = count; count += 1; so_far })
}

fn main() {
    let mut a = make_counter();
    let mut b = make_counter();
    println!("{} {}", a(), a());
    println!("{} {}", b(), b());
}

asfunctionsomeday.rs

fn make_counter() -> FnMut()->i32 {
    let mut count = 0;
    move || { let so_far = count; count += 1; so_far }
}

fn main() {
    let mut a = make_counter();
    let mut b = make_counter();
    println!("{} {}", a(), a());
    println!("{} {}", b(), b());
}