gistfile1.rs

fn call_f<F>(f: &F) -> i32 where F: ?Sized, F: Fn(i32) -> i32 {
    f(100)
}

fn main() {
    let f : Box<Fn(i32) -> i32> = Box::new(|&: x| 2 * x);
    let v : i32 = call_f(&*f);
    println!("{}", v);
}