#!/usr/bin/ruby -w
# include works on Modules, extend on Objects

module Mixin
  def foo
    puts "foo"
  end
end

module Aap
  def aap
    puts "aap"
  end
end

class Foo
  include Mixin
end


### extend usage 1
f = Foo.new
f.foo
f.extend(Aap)       # mix module Aap in _instance_ f of Foo
f.aap
g = Foo.new
#g.aap              # NameError, undefined method aap for Foo


### extend usage 2
class Bar
  # we're in Class instance Bar's scope, so
  # add Mixin's methods to Class instance Bar, not to instances of Bar.
  # essentially: call self.extend on Bar -> we're creating class methods
  extend Mixin
end

f = Bar.new
p Bar.methods.include?("foo") # true, foo is defined on Class instance Bar
p f.methods.include?("foo")   # false, foo is not defined on instance f
f.class.foo                   # call foo on Class instance Bar
Bar.foo                       # class method