include-and-extend-in-class.md

Include and Extend In Class

📓

Try to figure out difference between include and extend module in class:

module ExtendMethods
  def cmethod
    puts "class methods"
  end
end

module InstanceMethods
  def imethod
    puts "instance methods"
  end
end

module SingletonMethods
  def singleton_method
    puts "singleton methods"
  end
end

class M
  extend ExtendMethods
  include InstanceMethods
end

M.cmethod       #=> class methods
M.new.imethod   #=> instance methods

m = M.new.extend(SingletonMethods)
m.singleton_method   #=> singleton methods

In short, use extend to add class methods and include to add instance methods in your class. BTW, also can use extend to add singleton methods to a instance just like the above example.

Reference

• blog
• a book about ruby programming by this author