fn add_one(x: i32) -> i32 {
    x + 1
}

/// A function with a function pointer argument
fn do_twice(f: fn(i32) -> i32, arg: i32) -> i32 {
    f(arg) + f(arg)
}

#[derive(Debug)]
enum Status {
    Value(u32),
    Stop,
}

fn returns_closure() -> Box<dyn Fn (i32) -> i32> {
    Box::new(|x| x + 1)
}

fn main() {
    let answer = do_twice(add_one, 5);

    println!("The answer is: {}", answer);

    // Tuple Structs set up via function pointers
    let list_of_statuses: Vec<Status> =
        (0u32..20)
            .map(Status::Value)
            .collect();

    println!("List of statuses: {:?}", list_of_statuses);

    let increment = returns_closure();
    let x = 5;
    let y = increment(x);

    println!("The returned closure returns: {}", y);
}