Keep in mind that the potential expense of string concatenation was only _one_ example. There's a reason why I explicitly mentioned immutability: Rust's `Strin

Keep in mind that the potential expense of string concatenation was only _one_ example. There's a reason why I explicitly mentioned immutability: Rust's `String` type has more in common with C#'s `StringBuilder` class than it does with strings in most languages. Meanwhile, the behavour of str/&str is very different.