Nitpick: if you have a String and a &str, you want to convert the first to the second, not the other way around. Strings are owned, so &str to String does an allocation and copy of the bytes, while String to &str is a trivial operation that just throws away the capacity field.

But yeah, it would be nice if Rust had better ergonomics regarding coercing the insides of wrapper types. Though I'm not sure how exactly that would work.