References and Borrowing There is a new edition of the book and this is an old link. A reference refers to a value but does not own it. Because it does not own it, the value it points to will not be dropped when the reference goes out of scope. fn calculate_length(s: &String) -> usize { // s is a reference to a String s.len() } // Here, s goes out of scope. But because it does not have ownership o