Example of using include and extend in Ruby

using-include-vs-extend.rb

module WithInstanceMethod
  def whoami
    puts self.inspect
  end
end

class One
  include WithInstanceMethod
end

One.new.whoami # This will print an object id
puts One.instance_methods.include?(:whoami) # this will print true
puts One.methods.include?(:whoami) # this will print false

begin
  One.whoami # This class method does not exists, it only exists as instance method
rescue NoMethodError => e
  puts e
end


module WithClassMethod
  def load
    puts self.inspect
  end
end

class Two
  extend WithClassMethod
end

Two.load # This will print the class
puts Two.instance_methods.include?(:load) # this will print false
puts Two.methods.include?(:load) # this will print true

begin
  Two.new.load # This instance method does not exists, it only exists as class method
rescue NoMethodError => e
  puts e
end