Codefol.io

Ruby lets you hook in and see (and change!) a lot of behavior of the core language. Methods, constants, classes, variables… Ruby lets you query them all, and change a lot about them.

These are just hooks – things Ruby calls in response to something happening. That’s different from, say, all the methods you can call to find our what’s defined and how – like instance variables, or method bindings, or…

Here’s summaries and links for all the hooks I could find (thanks to Google and StackOverflow!):

ruby metaprogramming

There’s a semi-famous book, The Art of the Metaobject Protocol by Kiczales, des Rivieres and Bobrow. Alan Kay, the guy who invented SmallTalk and the phrase “Object Oriented”, called it the best book in ten years.

But it’s takes some describing.

What is a Metaobject Protocol?

You know how Ruby has a class called “Class”? And how all classes are instances of it? And how Class is a subclass of Module?

The Metaobject protocol asks, “what if there were more subclasses of Class? And you could make classes from them, instead of plain old Class?”

Also, it includes what we’d now call introspection functions – they didn’t usually call it that twenty years ago when this was published.

But what, specifically, does that mean?

ruby metaprogramming