Good explanation of ruby object model -- mainly, 'classes are objects'?

ruby

Solution

It means precisely what it sounds like — classes are objects. Specifically, they are instances of the class `Class`, which is itself a subclass of the class `Module`, which in turn is a subclass of `Object`, just like every other class in Ruby. Like any other object in Ruby, a class can respond to messages, have its own instance variables, etc.

As a practical example, let's take `private`.

class Person
  attr_accessor :name, :height
  private
  attr_accessor :weight
end

This gives instances of Person public methods to access the person's name and height, but the accessors for the person's weight are private. BUTBUTBUT — rather than being a keyword like in most languages, `private` is an ordinary method of the Module class. If we wanted, we could redefine it to do something different for a particular class hierarchy.

class RichardStallman
  def self.private(*args)
    puts "NO! INFORMATION WAS MEANT TO BE FREE!"
  end
end

Problem

I am studying the ruby object model and have some questions. I understand the idea that an object only stores instance variables, and methods are stored in the class, which an object has a reference to. I also understand the idea of 'self' -- what it is, how it changes, etc. However, what I don't understand is the notion that 'classes are objects.' Is there a good, intuitive explanation anywhere? (BTW: I'm using Ruby Object Model and Metaprogramming and Metaprogramming Ruby as my two resources. If anybody can suggest something else, that would be helpful.) Thanks.

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