fn pass_str(s: &str) -> &str {
    return s;
}
fn pass_string(s: String) -> String {
    return s;
}
fn main() {
    // using string literal
    let test: &str = "Hello world!";
    println!("{}", pass_str(test));

    // using string object
    let text: String = String::from("Goodbye world!");
    println!("{}", pass_string(text));
}