Don't mutate the input string, this behavior isn't normally expected unless specified explicitly.

Not an issue

Not an issue.

This kata is way too simple for a ruby, maybe do something where there is a nested set, and you have to use 2 block / proc objects

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

"To compare numbers instead of strings, the compare function can simply subtract b from a."

It is not very challenging