fn print_string(s: String) { // s takes ownership
    println!("Owned string: {}", s);
} // s is dropped here

fn borrow_string_immutable(s: &String) { // s borrows immutably
    println!("Borrowed immutably: {}", s);
}

fn borrow_string_mutable(s: &mut String) { // s borrows mutably
    s.push_str(" (modified)");
    println!("Borrowed mutably: {}", s);
}

fn main() {
    let s1 = String::from("Hello");
    print_string(s1); // s1's ownership moved to print_string, s1 is invalid after this
    // println!("{}", s1); // This would be a compile-time error!

    let mut s2 = String::from("World");
    borrow_string_immutable(&s2); // s2 is borrowed
    println!("Original s2 after immutable borrow: {}", s2);

    borrow_string_mutable(&mut s2); // s2 is borrowed mutably
    println!("Original s2 after mutable borrow: {}", s2);
}