quintuple.rs

// A function which takes a closure and returns an `i32`.
fn apply_to_n<F, T>(f: F, t: T) -> T where
    // The closure takes an `i32` and returns an `i32`.
    F: Fn(T) -> T {

    f(t)
}

fn main() {
    let double = |x| 2 * x;

    println!("2 quintupled: {}", apply_to_n::<Fn, i32>(double, 5)); // problem is probably with std::ops::Fn
}