Another one: class variables! # Define two class variables in two different classes: class MyClass @@base = 1 end class OtherClass

Another one: class variables! # Define two class variables in two different classes: class MyClass @@base = 1 end class OtherClass @@base = 2 end # Define it in the superclass too: class Object @@base = 3 end class MyClass # Magic! The subclass-variable has now changed! p @@base # => 3 end class OtherClass # In both classes in fact: p @@base # => 3 # And finally, let's reset this: @@base = 4 end class Object # Whoops, this changes the superclass too: p @@base # => 4 end Explanation: Two class variables with the same name can't exists in the same class hierachy. Therefore, class variable lookup (and setter) will always traverse to the upmost-class where the variable is defined. (Hope you don't mind that I wrote these in two different posts.)