fn doubled_iterator<'a>(slice: &'a[u32]) -> impl Iterator<Item=u32> + '_ {
    return slice.iter().map(|x| { return x * 2 });
}

fn main() {
    let numbers = vec![1, 2, 3];

    for number in doubled_iterator(&numbers) {
        println!("{}", number);
    }
}

fn test<'a>(slice: &'a[u32]) -> &'a [u32] {
    slice
}

fn testa(slice: &[u32]) -> &[u32] {
    slice
}