I loved Ruby Under a Microscope when I first read it, and using that knowledge was able to have fun with some CTFs years ago.

I haven't kept up with the evolving Ruby implementation internals, so I will sure as heck buy this new version of the book.

I used Ruby a lot from about 2002 to 2010. Haven't used it much since then, but this article really makes me want to get a copy of the upcoming version Ruby Under a Microscope.