Ruby: Include instance and class methods in a module.

example_include.rb

# using include to include both class methods and instance methods
# http://www.railstips.org/blog/archives/2009/05/15/include-vs-extend-in-ruby/

module Foo
  def self.included(base)
    base.extend(ClassMethods)
  end
  
  module ClassMethods
    def bar
      puts 'class method'
    end
  end
  
  def foo
    puts 'instance method'
  end
end

class Baz
  include Foo
end

Baz.bar # class method
Baz.new.foo # instance method
Baz.foo # NoMethodError: undefined method ‘foo’ for Baz:Class
Baz.new.bar # NoMethodError: undefined method ‘bar’ for #<Baz:0x1e3d4>