Explanation of some of the internals of ruby.

rubystuff.rb

public    # call from anywhere
protected # call from inside instance of a class
private   # only call implicitly from instance

Constants       # Not inherited, not changed

@@class_variables   # Inherited, changeable
   # Changes all sub and super classe as well!!

@class_instance_variables # Inherited, changable
   # Change only the current class,
   # not sub or super

class Array
  class << self
    # This is the SINGLTON of Array
    # singlton classes are the only instance of a given class.

    attr_accessor :class_instance_variable

    def class_method
    end
  end

  def public_instance_method
    self.class.class_instance_variable
    @@class_variable

    some_protected_method
    self.some_protected_method

    some_private_method
    # NO self.some_private_method
  end

  protected
  def some_protected_method
  end

  private
  def some_private_method
  end
end

# all classes are instances of Class
Array.class == Class
AnyClass.class == Class