Ruby Base.send calling it like instance method in model when using include and extend

Question

Ruby library code

module Yaffle
  module ActsAsYaffle
    def self.included(base)
        base.extend(ClassMethods)
    end

    module ClassMethods
      def acts_as_yaffle(options = {})
        cattr_accessor :yaffle_text_field
        self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s

        include Yaffle::ActsAsYaffle::LocalInstanceMethods
      end
    end

    ...
    more code
    ...
  end
end

ActiveRecord::Base.send(:include, ActiveRecord::Acts::Taggable)

Why does when i call the acts_as_yaffle in the model, its being used like

class Hickwall < ActiveRecord::Base
   acts_as_yaffle
end

Does the ActiveRecord::Base.send(:include,...) included the ClassMethods as instance eventhough the base is extended (base.extend(ClassMethods) ? The acts_as_yaffle was declared as a ClassMethods.

Answer 1

It is a class method. Consider this example:

class C
  def my_instance_method
    puts 'hello from instance'
  end

  def self.my_class_method
    puts 'hello from class'
  end

  my_instance_method
  # NoMethodError

  my_class_method
  # hello from class
end

inside class C ... end you can only call class methods, because there is no instance to send the method call to. The library code is written using a common pattern to put class methods inside a module. For better understanding, the example class I wrote above is equivalent to this:

module M
  def my_instance_method
    puts 'hello from instance'
  end

  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods
    def my_class_method
      puts 'hello from class'
    end
  end
end