fn main() {
    let counts = vec![3_u32, 5, 8];
    let doubled: Vec<u32> = counts.iter().map(|n| n * 2).collect();
    assert_eq!(doubled, vec![6, 10, 16]);
    assert_eq!(counts.len(), 3);
    println!("Borrowed counts transformed to 6, 10, 16");
}