fn first_word(a: &str) -> &str {
    println!("{}", a);
    "hi"
}

fn first_word(s: &String) -> &str {
    let bytes = s.as_bytes();

    for (i, &item) in bytes.iter().enumerate() {
        if item == b' ' {
            return &s[0..i];
        }
    }

    &s[..]
}

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

    let word = first_word(&s);

    s.clear(); // error!

    println!("the first word is: {}", word);
}

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

//     let word = first_word(&s); // word will get the value 5

//     s.clear(); // this empties the String, making it equal to ""

//     // word still has the value 5 here, but there's no more string that
//     // we could meaningfully use the value 5 with. word is now totally invalid!
// }