Yeah in my original post (before the edit) I made a similar simplification with immutable vs mutable (since that's how they are commonly used), but the correct

Yeah in my original post (before the edit) I made a similar simplification with immutable vs mutable (since that's how they are commonly used), but the correct distinction is str vs String. You can have &str and &String and you can have &mut str and &mut String, and Box<str> and String. All cases exist.