# Include and Extend Again **URL:** \ **Category:** Ruby\ **Created:** [November 7, 2006, 11:06am UTC](https://www.ruby-forum.com/t/include-and-extend-again/75024 "2006-11-07T11:06:36Z")\ **Posts on this page:** 4\ **Page:** 1

**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\ **Post date:** [November 7, 2006, 11:06am UTC](https://www.ruby-forum.com/t/include-and-extend-again/75024/1 "2006-11-07T11:06:36Z")

Hi all, I must be really thick with this because I cannot get my class to behave. What I want to do is class AClass include AModule end and have that module mixin both instance and class methods. I’ve seen this done, but obviously I don’t understand what’s really going on because I can’t make it happen. I know this has been discussed on the list before as well. I’ve reviewed that as well. I fell really thick with this one. It’s just not going in. Here’s what I’ve tried (don’t worry it’s short). I put this into a single file and just run it. Any pointers to the source of my misunderstanding would be great. Thanx module A def self.included(base) base.extend ClassMethods base.send( :include, InstanceMethods ) end module InstanceMethods def b puts “I’m an instance method” end end module ClassMethods def a puts “I’m a class method” end end end class Object include A end require ‘test/unit’ class MyModuleTest \< Test::Unit::TestCase def test\_object\_should\_have\_the\_a\_method\_as\_class\_method assert Object.respond\_to?( :a ) end ``` def test_object_should_not_have_the_a_method_as_instance_method assert !Object.new.respond_to?( :a ) end def test_object_should_have_the_b_method_as_instance_method assert Object.new.respond_to?( :b ) end def test_object_should_not_have_the_b_method_as_class_method assert !Object.respond_to?( :b ) end ``` end require ‘test/unit/ui/console/testrunner’ Test::Unit::UI::Console::TestRunner.run(MyModuleTest) ---

On 11/6/06, Daniel N [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > and have that module mixin both instance and class methods. I’ve seen this > > ``` > end > > ``` > > end > > module ClassMethods > def a > puts “I’m a class method” > end > end > > end ``` class AClass ``` > ``` > include A > > ``` > > end > > require ‘test/unit’ > > class MyModuleTest \< Test::Unit::TestCase > def test\_object\_should\_have\_the\_a\_method\_as\_class\_method > assert AClass.respond\_to?( :a ) > end > > ``` > def test_object_should_not_have_the_a_method_as_instance_method > > ``` ``` assert !AClass.new.respond_to?( :a ) ``` > ``` > end > > def test_object_should_have_the_b_method_as_instance_method > > ``` ``` assert AClass.new.respond_to?( :b ) ``` > ``` > end > > def test_object_should_not_have_the_b_method_as_class_method > > ``` ``` assert !AClass.respond_to?( :b ) ``` > ``` > end > > ``` > > end > > require ‘test/unit/ui/console/testrunner’ > Test::Unit::UI::Console::TestRunner.run(MyModuleTest) Your problem is, that Class.is\_a? Object i.e. object Class is an instance of class Object. Therefore all instance methods of Object are class methods (or vice versa, I’m getting lost a bit 😉 Second issue: your instance methods: you can simply put them in main A module (as rails does), or add include InstanceMethods line at the end of A module definition and thus you can leave out the base.send(:include) line module A … include InstanceMethods end ---

On 11/7/06, Jan S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Your problem is, that Class.is\_a? Object i.e. object Class is an > instance of class Object. > Therefore all instance methods of Object are class methods (or vice > versa, I’m getting lost a bit 😉 Well that works a treat. I changed the class definition to class Thing include A end and it worked great. The incestuous relationship between Object and Class has not really raised it’s head as a problem for me before so it didn’t even enter my mind. Thanx for pointing it out. Second issue: your instance methods: you can simply put them in main A > module (as rails does), or add include InstanceMethods line at the end > of A module definition and thus you can leave out the > base.send(:include) line Thanx for that. I had a feeling that might be the case. With the other error I was just unsure. module A > … > include InstanceMethods > end > > Thanx very much for your reply. Daniel ---

On 11/6/06, Daniel N [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > class Thing > > > of A module definition and thus you can leave out the > > > > Thanx very much for your reply. Just to be clear: IMO your problem is the first issue - the Object and Class relationship. The second issue is just a cosmetic change, and has no impact on whether it works or not. The difference is a) aesthetical b) how many time the InstanceMethod module is included - either into any object/class that includes A or just once into A and _through_ it into other objects.