A Rust `String` reference (i.e. &String) can always be passed where `&str` is expected because `String` has a `Deref<Target=str>` impl... in that sense they don

A Rust `String` reference (i.e. &String) can always be passed where `&str` is expected because `String` has a `Deref<Target=str>` impl... in that sense they don't just appear similar, they are polymorphic.