fn main() {
    let s1 = String::from("hello");
    let s2 = s1; // s1 moved to s2, s1 no longer valid

    println!("{}", s2); // OK
    // println!("{}", s1); // Error: value borrowed after move
}

fn main() {
    let s1 = String::from("hello");

    let len = calculate_length(&s1); // Borrow s1

    println!("Length of '{}' is {}", s1, len); // s1 still valid
}

fn calculate_length(s: &String) -> usize {
    s.len()
} // s goes out of scope but nothing happens (doesn't own the data)

fn main() {
    let mut s = String::from("hello");

    change(&mut s);

    println!("{}", s); // "hello, world"
}

fn change(s: &mut String) {
    s.push_str(", world");
}

fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}