Ruby modules, classes, and instance methods

bar.rb

# An example of class/instance methods w/ modules
module Foo
  def self.included(base)
    base.extend(ClassMethods)
  end

  def foo
    puts 'Bar.new.foo prints this'
  end

  def self.foo
    puts 'Foo.foo prints this'
  end

  module ClassMethods
    def foo
      puts 'Bar.foo prints this'
    end
  end
end

class Bar
  include Foo
end

Bar.new.foo
Bar.foo
Foo.foo