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> So is Class an instance of itself? I don understand the logic behind
> this :(


Well then you'll love this:

Class.class
#=> Class

Class.superclass
#=> Module

Class.superclass.superclass
#=> Object

Module.class
#=> Class

Object.class
#=> Class

Object.ancestors
#=> [Object, Kernel]

Kernel.class
#=> Module

So Object and Module are instances of a subclass of themselves, and Object
inherits from Kernel, which is a Module, a subclass of Object. Fun!

The way this actually works is that a Ruby interpreter will implement Object
using low-level building blocks, then implement Module and Class on top of
that, then perform a bunch of voodoo to make Object and Module *look* like
first-class Class instances.

Some quick rules on Ruby's type system that I find helpful:

* Object is the base type. Everything is an Object.

* Module is a type of Object that stores Methods. A module contains a list
of methods, and possibly pointers to one or more 'parent' modules mixed in
using `include`.

* Class is a type of Module that not only stores Methods but can also spawn
new Objects that have the class's methods. Additionally, classes have extra
inheritance semantics in that subclassing is more restrictive than mixins,
and class methods are inherited when subclassing.

* Kernel is an *instance* of Module that stores the core methods common to
all Objects. It is mixed into Object after Module is created, thereby adding
the core methods to all extant objects in the Ruby runtime.

--
James Coglan
http://jcoglan.com

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