one_shot.rs

struct OneShot<S, T> (S, ~fn (S) -> T);

impl<S, T> OneShot<S,T> {
    fn run(~self) -> T {
        let (s, f) = match self {
            ~OneShot(s, f) => (s,f)
        };

        f(s)
    }
}

fn one_shot<T,S>(e: S, f: ~fn(S) -> T) -> ~OneShot<S, T> {
    ~OneShot(e,f)
}

fn test(a:~int) -> ~OneShot<~int, ~str> {
    let b = 2, c = ~10;

    one_shot(a, |a| {
        fmt!("%d", ~a + b + *c)
    })
}

fn main() {

    let t = test(~10);
    let r = t.run();
    //let _ = t.run(); this causes an error because of the move
    io::println(fmt!("%?", r));
}