I believe that without self it would not know what iterable object it was iterating over.

So without specifying 'self' it just forwards it to the existing upcase method?

..I thought the point of this kata was rewriting the upcase method?

very clever

Using symbols as keys for the hashes indeed would make more sense.

Marked your comment "spoiler" since this got rid of the annoying alert you put up.

It seems, you just accidentally broke the codewars

I guess you can enter script tag in codewars comments too..

I have no idea what I just did. Stupid kata.

Unfortunately it's clear the Author doesn't code in Ruby

sort doesn't use Schwartzian transform as sort_by, so sorting takes longer