fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}
fn main() {
    // lifetime 'a
    let s1 = "asdas".to_string();

    // lifetime 'a (like return type of longest func)
    let result;
    {
        // lifetime 'b
        let s2 = "hello wrlld".to_string();

        //                 'a      'b
        result = longest(&s1, &s2);
        //                 cannot to that
    }
    println!("result: {}", result);
}