Difference between include and extend

In Ruby, a Module is a collection of methods and constants. We useincludetomixinthe module with the current class. Aftermixin, the current class can use the methods and constants from the module, and any subclass of the current class can also inherit the methods and constants of the module.

module Talkable
  def say_hi
    puts "Hi"
  end
end

class Example
  include Talkable
end

Example.new.say_hi
#=> Hi

Example.say_hi
# NoMethodError: undefined method `say_hi’ for Example:Class
# from (irb):17
# from /usr/local/bin/irb:11:in `<main>’

Note: By using include, the module addinstancemethod to the class.

Unlikeinclude, which adds module’s methods as instance methods ,extend allows you to add them as a class methods.

module Talkable
  def say_hi
    puts "Hi"
  end
end
class Experiment
  extend Talkable
end

Experiment.say_hi
#=> Hi

Experiment.new.say_hi
# NoMethodError: undefined method `say_hi’ for #<Experiment:0x007fc6b90e5178>
# from (irb):16
# from /usr/local/bin/irb:11:in `<main>’

Resource:Ruby Require VS Load VS Include VS Extend