#[derive(Debug)]
struct User { name: String, age: u32 }

fn main() {
    let mut users = vec![
        User { name: "Alice".into(), age: 31 },
        User { name: "Bob".into(),   age: 24 },
        User { name: "Eve".into(),   age: 42 },
    ];

    users.sort_by_key(|u| u.age);

    for u in &users {
        println!("{:?}", u);
    }
}