// This will give us the Error that string2 did not live long enough
// So that we can find where it happens
// We declare a lifetime named 'a (it can be any letter, but 'a is standard)
fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}

fn main() {
    let string1 = String::from("long_string_here");
    let result;
    
    {
        let string2 = String::from("short");
        result = longest(string1.as_str(), string2.as_str()); 
    } // string2 is dropped here
    
    // ERROR: string2 is dead, so result is invalid.
    println!("The longest string is {}", result); 
}