# How to get modules included by a class/module (not those fro

**URL:** <https://www.ruby-forum.com/t/how-to-get-modules-included-by-a-class-module-not-those-fro/87183>\
**Category:** Ruby\
**Created:** [February 28, 2007, 6:33pm UTC](https://www.ruby-forum.com/t/how-to-get-modules-included-by-a-class-module-not-those-fro/87183 "2007-02-28T18:33:32Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![rubarachni](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/74df32/32.png) [@rubarachni](https://www.ruby-forum.com/u/rubarachni)\
**Post date:** [February 28, 2007, 6:33pm UTC](https://www.ruby-forum.com/t/how-to-get-modules-included-by-a-class-module-not-those-fro/87183/1 "2007-02-28T18:33:32Z")

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Is there a way to get only the modules included by a given class.  
Using included\_modules returns also the modules that are included by  
the superclass(es).

Example :  
class MyClass  
end  
MyClass.included\_modules

# will return Kernel

As a given module may be included several times in the class hierarchy  
(e.g. by the class and by one of its superclass), just getting all  
included modules and removing the included modules from the superclasses  
may not be a solution. The given module may have been removed  
erroneously.

It would have been great if included\_modules takes a boolean parameter  
in order to disable the recursion like instance\_methods for example.

Thanks for any help.

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**Author:** ![rubarachni](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/74df32/32.png) [@rubarachni](https://www.ruby-forum.com/u/rubarachni)\
**Post date:** [February 28, 2007, 8:29pm UTC](https://www.ruby-forum.com/t/how-to-get-modules-included-by-a-class-module-not-those-fro/87183/2 "2007-02-28T20:29:53Z")

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Ruby A. schrieb:

> Is there a way to get only the modules included by a given class.  
> Using included\_modules returns also the modules that are included by  
> the superclass(es).  
> (…)  
> As a given module may be included several times in the class  
> hierarchy (e.g. by the class and by one of its superclass), just  
> getting all included modules and removing the included modules from  
> the superclasses may not be a solution. The given module may have  
> been removed erroneously.

Including a module in a class that already has been included by one of  
its superclasses doesn’t change the inheritance hierarchy:

module M  
end

class P  
include M  
end

class C \< P  
end

p C.ancestors # =\> [C, P, M, Object, Kernel]

class C  
include M  
end

p C.ancestors # =\> [C, P, M, Object, Kernel]

The only way to create the situation you describe above would be to  
include the module in the child class _before_ including it in the  
superclass. If you want to detect this, you could try the following  
code:

class Class  
def my\_own\_included\_modules  
ancestors.inject([]) { |acc, mod|  
break acc if mod == superclass  
acc \<\< mod unless mod == self  
acc  
}  
end  
end

p P.my\_own\_included\_modules # =\> [M]  
p C.my\_own\_included\_modules # =\> []

class P2  
end

class C2 \< P2  
include M  
end

class P2  
include M  
end

p C2.ancestors # =\> [C2, M, P2, M, Object, Kernel]

p P2.my\_own\_included\_modules # =\> [M]  
p C2.my\_own\_included\_modules # =\> [M]

Out of curiosity: why do you need this?

Regards,  
Pit

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**Author:** ![rubarachni](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/74df32/32.png) [@rubarachni](https://www.ruby-forum.com/u/rubarachni)\
**Post date:** [February 28, 2007, 11:48pm UTC](https://www.ruby-forum.com/t/how-to-get-modules-included-by-a-class-module-not-those-fro/87183/3 "2007-02-28T23:48:38Z")

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Pit,

> Including a module in a class that already has been included by one of  
> its superclasses doesn’t change the inheritance hierarchy:
> 
> module M  
> end
> 
> class P  
> include M  
> end
> 
> class C \< P  
> end
> 
> p C.ancestors # =\> [C, P, M, Object, Kernel]
> 
> class C  
> include M  
> end
> 
> p C.ancestors # =\> [C, P, M, Object, Kernel]
> 
> The only way to create the situation you describe above would be to  
> include the module in the child class _before_ including it in the  
> superclass.

You are absolutely right ! I did not catch this.  
This seems to be a similar behaviour as for a class variable/method :

class B  
@@var = “Hello”  
end

class C \< class B  
end

The class variable @@var is shared/inherited in C. Similar as the case  
where there is only one include.

Conversely :

class B  
end

class C \< class B  
@@var = “Hello”  
end

class B  
@@var = “Goodbye”  
end

The two class variables @@var are different. This is similar as the case  
where there is an include at each class.

I know that this behaviour for class variable/method will change with  
Ruby 2.0.  
(A class variable/method will be static to the class)  
Will it be the same for module inclusion ??

> class Class  
> def my\_own\_included\_modules  
> ancestors.inject([]) { |acc, mod|  
> break acc if mod == superclass  
> acc \<\< mod unless mod == self  
> acc  
> }  
> end  
> end

This is exactly what I need.

> Out of curiosity: why do you need this?

I just want to know/understand :

- the hierarchy (inheritance) between the Ruby classes
- which class really includes which module(s)

Thanks a lot.

Chauk-Mean.

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**Author:** ![rubarachni](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/74df32/32.png) [@rubarachni](https://www.ruby-forum.com/u/rubarachni)\
**Post date:** [March 1, 2007, 4:03pm UTC](https://www.ruby-forum.com/t/how-to-get-modules-included-by-a-class-module-not-those-fro/87183/4 "2007-03-01T16:03:45Z")

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> class C \< P  
> rick@frodo:~$ ruby1.8 modtest.rb  
> [C, P, M, Object, Kernel]  
> [C, P, M, Object, Kernel]  
> rick@frodo:~$ ruby1.9 modtest.rb  
> [C, P, M, Object, Kernel, BasicObject]  
> [C, M, P, M, Object, Kernel, BasicObject]

Thanks for your reply.  
This is what I expected as this is consistent with the new class  
var/methods behaviour.

> I wrote about this back in October  
> [http://talklikeaduck.denhaven2.com/articles/2006/10/09/a-subtle-change-to-mixin-semantics-in-ruby-1-9](http://talklikeaduck.denhaven2.com/articles/2006/10/09/a-subtle-change-to-mixin-semantics-in-ruby-1-9)

Oups ! I just created a new thread on this subject.

Maybe we will get some official/more up to date position as I haven’t  
found any mention on this change on the report from EigenClass “Changes  
of Ruby 1.9 update 6”.

Chauk-Mean.

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**Author:** ![rubarachni](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/74df32/32.png) [@rubarachni](https://www.ruby-forum.com/u/rubarachni)\
**Post date:** [March 1, 2007, 3:24pm UTC](https://www.ruby-forum.com/t/how-to-get-modules-included-by-a-class-module-not-those-fro/87183/5 "2007-03-01T15:24:39Z")

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On 2/28/07, Pit C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> class C \< P  
> end
> 
> p C.ancestors # =\> [C, P, M, Object, Kernel]
> 
> class C  
> include M  
> end
> 
> p C.ancestors # =\> [C, P, M, Object, Kernel]

This has changed in 1.9 (or at least as of a few months ago which was  
the last time I built 1.9)

rick@frodo:~$ cat modtest.rb  
module M  
end

class P  
include M  
end

class C \< P  
end

p C.ancestors

class C  
include M  
end

p C.ancestors

rick@frodo:~$ ruby1.8 modtest.rb  
[C, P, M, Object, Kernel]  
[C, P, M, Object, Kernel]  
rick@frodo:~$ ruby1.9 modtest.rb  
[C, P, M, Object, Kernel, BasicObject]  
[C, M, P, M, Object, Kernel, BasicObject]

I wrote about this back in October  
[http://talklikeaduck.denhaven2.com/articles/2006/10/09/a-subtle-change-to-mixin-semantics-in-ruby-1-9](http://talklikeaduck.denhaven2.com/articles/2006/10/09/a-subtle-change-to-mixin-semantics-in-ruby-1-9)

–  
Rick DeNatale

My blog on Ruby  
[http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)

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**Author:** ![rubarachni](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/74df32/32.png) [@rubarachni](https://www.ruby-forum.com/u/rubarachni)\
**Post date:** [March 1, 2007, 5:35pm UTC](https://www.ruby-forum.com/t/how-to-get-modules-included-by-a-class-module-not-those-fro/87183/6 "2007-03-01T17:35:58Z")

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On 3/1/07, Ruby A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > class C \< P  
> > rick@frodo:~$ ruby1.8 modtest.rb  
> > [C, P, M, Object, Kernel]  
> > [C, P, M, Object, Kernel]  
> > rick@frodo:~$ ruby1.9 modtest.rb  
> > [C, P, M, Object, Kernel, BasicObject]  
> > [C, M, P, M, Object, Kernel, BasicObject]
> 
> Thanks for your reply.  
> This is what I expected as this is consistent with the new class var/methods behaviour.

Actually, I just checked out the latest version of the 1.9 trunk code,  
and it seems to have gone back:.

rick@frodo:~$ ruby1.9 modtest.rb  
[C, P, M, Object, Kernel, BasicObject]  
[C, P, M, Object, Kernel, BasicObject]

I’m not sure why, personally I thought that the way 1.9 used to work  
was more natural.

–  
Rick DeNatale

My blog on Ruby  
[http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)