# Klass.include vs instance.extend question

**URL:** <https://www.ruby-forum.com/t/klass-include-vs-instance-extend-question/59540>\
**Category:** Ruby\
**Created:** [May 3, 2006, 11:35pm UTC](https://www.ruby-forum.com/t/klass-include-vs-instance-extend-question/59540 "2006-05-03T23:35:58Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![polypus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/b5ac83/32.png) [@polypus](https://www.ruby-forum.com/u/polypus)\
**Post date:** [May 3, 2006, 11:35pm UTC](https://www.ruby-forum.com/t/klass-include-vs-instance-extend-question/59540/1 "2006-05-03T23:35:58Z")

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i want a few instance methods to be automatically defined for the user  
without any explicit coding on their part.

in the below distillation of my code, i have two options (labelled), my  
question  
is whether one option is better in any way than the other, and why one  
would prefer one over the other. my suspicion is that option 1 is more  
space efficient, and option 2 more time efficient, is that correct?

also i should note that for people to use my module M they must call  
(for other reasons) extend, foo, and init\_m in the extended class  
regardless of which option i finally choose. also the method init\_m must  
be defined in the manner below (define\_method) regardless of the option  
i choose, also for other reasons. and so you should not take any of  
their having to be there or not into account in your assesment. thanks  
many.

module InstanceMethods

# instance methods in here

end

module M

# option 1

def self.extend\_object klass  
klass.class\_eval ‘include InstanceMethods’  
super  
end

# option 2

def foo  
define\_method :init\_m do  
self.extend InstanceMethods  
end  
end

end

class X  
extend M  
foo  
def intialize  
init\_m  
end  
end

---

<div class="post-metadata">

**Author:** ![polypus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/b5ac83/32.png) [@polypus](https://www.ruby-forum.com/u/polypus)\
**Post date:** [May 5, 2006, 10:51pm UTC](https://www.ruby-forum.com/t/klass-include-vs-instance-extend-question/59540/2 "2006-05-05T22:51:55Z")

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2006/5/3, polypus [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> also i should note that for people to use my module M they must call
> 
> ```
> end
> 
> ```
> 
> end  
> Why can’t you just do

class X  
include InstanceMethods  
end

Did I miss something?

robert

---

<div class="post-metadata">

**Author:** ![polypus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/b5ac83/32.png) [@polypus](https://www.ruby-forum.com/u/polypus)\
**Post date:** [May 6, 2006, 4:58am UTC](https://www.ruby-forum.com/t/klass-include-vs-instance-extend-question/59540/3 "2006-05-06T04:58:51Z")

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> Did I miss something?

ok forget all of my above code. i’ve solved that problem in another  
thread, see ‘mixin puzzle’.

but i would still like to know when one would prefer extending the  
individual objects instead of ‘including’ into their class (and vice  
versa), and what the pros and cons of each method are.

thanks,  
\_c

---

<div class="post-metadata">

**Author:** ![polypus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/b5ac83/32.png) [@polypus](https://www.ruby-forum.com/u/polypus)\
**Post date:** [May 6, 2006, 7:56am UTC](https://www.ruby-forum.com/t/klass-include-vs-instance-extend-question/59540/4 "2006-05-06T07:56:03Z")

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2006/5/6, polypus [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> > Did I miss something?
> 
> ok forget all of my above code. i’ve solved that problem in another  
> thread, see ‘mixin puzzle’.
> 
> but i would still like to know when one would prefer extending the  
> individual objects instead of ‘including’ into their class (and vice  
> versa), and what the pros and cons of each method are.

Well, the answe is pretty obvious: if you need all instances of a  
class to have these methods you’ll certainly want to include the  
module in the class. If you just want to modify individual objects  
then you extend them on a one by one basis.

And I guess extending individual objects is less efficient (at least  
memory wise) than doing it on the class level.

robert