#![feature(existential_type)]

existential type ClonedIter<'a, T>: Iterator<Item = T>;
existential type MulIter<I>: Iterator<Item = i32>;

fn cloned_iter<T: Clone>(x: &[T]) -> ClonedIter<'_, T> {
    x.iter().cloned()
}

fn mul_iter<I>(x: I, a: i32) -> MulIter<I>
where
    I: IntoIterator<Item = i32>,
{
    x.into_iter().map(move |x| x * a)
}

struct Ok<I>(MulIter<I>);

fn main() {
    let x = cloned_iter(&["Hello", "World"]);
    println!("{}", x.collect::<String>());

    let a = cloned_iter(&[1, 2, 3, 4]);
    let b = mul_iter(a, 3);
    let ok_wrapped = Ok(b);
    for x in ok_wrapped.0 {
        println!("{}", x);
    }
}