Great question, I'd like to know too. Sometimes I poke around popular open source projects, like the rails source. Here's how they implemented the syntatic sugar for things like "1.month.from_now":

http://github.com/rails/rails/tree/master/activesupport/lib/...

I recently found http://refactormycode.com/ and it looks interesting for learning, though not comprehensive. Sometimes it's nice to see the "before and after".