From: James Harrison <oscartheduck@...>
Date: 2010-08-01T11:24:56+09:00
Subject: Re: what is the correct way to extend native methods?

>    return self.select{ |val| val.to_s =~ args[0] } if args.size == 1
> and args[0].is_a?(RegExp)

Try Regexp, not RegExp

http://ruby-doc.org/core/classes/Regexp.html