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Rust 1.26.0

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
} // Here, s goes out of scope. But because it does not have ownership of what
  // it refers to, nothing happens.Run

Here are the relevant sections in the new and old books: