foobar.rb

# I'm extending two classes with the same module which refers to a 
# class variable. The trouble is that both of them seem to share the
# same variable, instead of having one for each class.
#
# How do I give them one each?
# 
# (using Ruby 2.2.2)

module Widgets

  def widgets
    @@widgets ||= {}
  end  

  def add_widget(name, widget)
    self.widgets[name] = widget
  end 

end 

class Foo

  extend Widgets

end 

class Bar

  extend Widgets

end 

Foo.add_widget('foo', :bar)

# How do I stop this happening?
Bar.widgets['foo']
# => :bar