# Is there a possibility to include methods of a class?

**URL:** <https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906>\
**Category:** Ruby\
**Created:** [May 11, 2007, 3:28pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906 "2007-05-11T15:28:59Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/977dab/32.png) [@bernd](https://www.ruby-forum.com/u/bernd)\
**Post date:** [May 11, 2007, 3:28pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906/1 "2007-05-11T15:28:59Z")

</div>

Hi all,  
first of all: this list and you rock! I know that there is no multiple  
inheritance, but you can use the concept of mixin.  
However, I want to inherit my class another and “mixin” methods from  
another class.  
To be more precise,  
I have a class that inherits another one (that comes from a library and  
I do not want to change) and I want the methods of ActiveRecord::Base in  
my class. Is there a way to do that (without copying and paste the whole  
ActiveRecord::Base class and changing it to a module)?

Thanks in advance!

---

<div class="post-metadata">

**Author:** ![bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/977dab/32.png) [@bernd](https://www.ruby-forum.com/u/bernd)\
**Post date:** [May 11, 2007, 3:58pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906/2 "2007-05-11T15:58:29Z")

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Bernd pisze:

> Thanks in advance!

Yes, You can use evil ruby [http://rubyforge.org/projects/evil](http://rubyforge.org/projects/evil)  
like this:  
class Bar  
include Array.as\_module  
end

b = Bar.new  
b.push(1,2,3)  
p b # =\> [1,2,3]

but this is bad resolve of your problem.

---

<div class="post-metadata">

**Author:** ![bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/977dab/32.png) [@bernd](https://www.ruby-forum.com/u/bernd)\
**Post date:** [May 11, 2007, 4:28pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906/3 "2007-05-11T16:28:02Z")

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Mariusz Pietrzyk wrote:

> Bernd pisze:
> 
> > Thanks in advance!
> 
> Yes, You can use evil ruby [http://rubyforge.org/projects/evil](http://rubyforge.org/projects/evil)  
> like this:  
> class Bar  
> include Array.as\_module  
> end
> 
> b = Bar.new  
> b.push(1,2,3)  
> p b # =\> [1,2,3]
> 
> but this is bad resolve of your problem.

I just thought, if there is a possibility to do dynamic inheritance like

def some\_method  
Some\_class \< ActiveRecord::Base  
end

---

<div class="post-metadata">

**Author:** ![bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/977dab/32.png) [@bernd](https://www.ruby-forum.com/u/bernd)\
**Post date:** [May 11, 2007, 5:14pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906/4 "2007-05-11T17:14:44Z")

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On Fri, May 11, 2007 at 10:29:01PM +0900, Bernd wrote:

> Hi all,  
> first of all: this list and you rock! I know that there is no multiple  
> inheritance, but you can use the concept of mixin.  
> However, I want to inherit my class another and “mixin” methods from  
> another class.  
> To be more precise,  
> I have a class that inherits another one (that comes from a library and  
> I do not want to change) and I want the methods of ActiveRecord::Base in  
> my class. Is there a way to do that (without copying and paste the whole  
> ActiveRecord::Base class and changing it to a module)?

I would use delegation for one class or the other.

That is: define your class as

class Foo \< ActiveRecord::Base  
…  
def initialize  
@other = Library::Bar.new  
end  
end

Or vice versa, whichever makes more sense. And if you can’t choose, then  
delegate to both.

class FooDB \< ActiveRecord::Base  
… more stuff  
end

class Foo  
def initialize(id)  
@db = FooDB.find(id)  
@lib = Library::Bar.new  
end  
end

Then the interface that Foo exposes to the world can pass some calls to  
@db,  
some to @lib, or (the best news) can combine behaviours from both in  
whichever way it likes.

---

<div class="post-metadata">

**Author:** ![bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/977dab/32.png) [@bernd](https://www.ruby-forum.com/u/bernd)\
**Post date:** [May 11, 2007, 5:29pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906/5 "2007-05-11T17:29:53Z")

</div>

Brian C. wrote:

> On Fri, May 11, 2007 at 10:29:01PM +0900, Bernd wrote:
> 
> > Hi all,  
> > first of all: this list and you rock! I know that there is no multiple  
> > inheritance, but you can use the concept of mixin.  
> > However, I want to inherit my class another and “mixin” methods from  
> > another class.  
> > To be more precise,  
> > I have a class that inherits another one (that comes from a library and  
> > I do not want to change) and I want the methods of ActiveRecord::Base in  
> > my class. Is there a way to do that (without copying and paste the whole  
> > ActiveRecord::Base class and changing it to a module)?
> 
> I would use delegation for one class or the other.
> 
> That is: define your class as
> 
> class Foo \< ActiveRecord::Base  
> …  
> def initialize  
> @other = Library::Bar.new  
> end  
> end
> 
> Or vice versa, whichever makes more sense. And if you can’t choose, then  
> delegate to both.
> 
> class FooDB \< ActiveRecord::Base  
> … more stuff  
> end
> 
> class Foo  
> def initialize(id)  
> @db = FooDB.find(id)  
> @lib = Library::Bar.new  
> end  
> end
> 
> Then the interface that Foo exposes to the world can pass some calls to  
> @db,  
> some to @lib, or (the best news) can combine behaviours from both in  
> whichever way it likes.

This is the workaround I just had so far, and now I want to get rid of  
it.

I have two classes:  
class Myclass \< ActiveRecord::Base  
def self.find(number)  
Anotherclass.find(number)  
end

class Anotherclass \< SAP4Rails::Base  
def self.find(number)  
do something  
end

But this solution to me seems to be so un-ruby!

As SAP4Rails::Base does not have an explicit superclass, I wondered, if  
there is some way to inject it dynamically a super class, because I need  
some other methods from ActiveRecord in another application  
I know that I could just alter the SAP4Rails class, but I want it in the  
way, that you just need ActiveRecord, SAP4RAils and my piece of code.

---

<div class="post-metadata">

**Author:** ![bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/977dab/32.png) [@bernd](https://www.ruby-forum.com/u/bernd)\
**Post date:** [May 11, 2007, 6:01pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906/6 "2007-05-11T18:01:50Z")

</div>

Mariusz Pietrzyk wrote:

> Bernd pisze:
> 
> > Thanks in advance!
> 
> Yes, You can use evil ruby [http://rubyforge.org/projects/evil](http://rubyforge.org/projects/evil)  
> like this:  
> class Bar  
> include Array.as\_module  
> end
> 
> b = Bar.new  
> b.push(1,2,3)  
> p b # =\> [1,2,3]
> 
> but this is bad resolve of your problem.

I think that would be the ruby way, following the principle of least  
surprise. Unfortunately, neither Array nor ActiveRecord::Base do have an  
“as\_module” method ☹

---

<div class="post-metadata">

**Author:** ![bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/977dab/32.png) [@bernd](https://www.ruby-forum.com/u/bernd)\
**Post date:** [May 11, 2007, 6:20pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906/7 "2007-05-11T18:20:51Z")

</div>

On Sat, May 12, 2007 at 12:30:00AM +0900, Bernd B. wrote:

> def self.find(number)  
> do something  
> end
> 
> But this solution to me seems to be so un-ruby!

You seem to be doing something very strange in the above code. You are  
replacing one of ActiveRecord::Base’s most fundamental operations - load  
from database by ID - with something which does something completely  
different.

Are you also going to overwrite the save and update methods? In which  
case,  
what functionality from ActiveRecord::Base do you actually want to keep?

I am guessing that SAP4Rails is some sort of remote-procedure call  
wrapper.  
That is, an instance of SAP4Rails::Base represents an object on some  
remote  
SAP server. If that’s true, I don’t see how it makes sense to try to mix  
that with another object which represents a row in a local SQL database.

If Myclass represents something which may exist in the local database  
and/or  
in the remote SAP system, then I’d very much go for delegation.

class MyDb \< ActiveRecord::Base; end  
class MySap \< SAP4Rails::Base; end

class Myclass  
def self.find(number)  
@rec = MyDb.find(number)  
@sap = MySap.find(number)  
end  
end

Then you are making it explicit that you are talking about two different  
things, and you can implement useful operations (such as copy data from  
one  
to the other)

Regards,

Brian.

---

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**Author:** ![bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/977dab/32.png) [@bernd](https://www.ruby-forum.com/u/bernd)\
**Post date:** [May 11, 2007, 6:42pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906/8 "2007-05-11T18:42:53Z")

</div>

On Sat, May 12, 2007 at 01:19:26AM +0900, Brian C. wrote:

> > class Anotherclass \< SAP4Rails::Base
> 
> Then you are making it explicit that you are talking about two different  
> things, and you can implement useful operations (such as copy data from one  
> to the other)

P.S. Something which may be relevant as an example is ActiveResource.

This is a REST XML client library, which presents an API very similar to  
ActiveRecord: e.g.

class Foo \< ActiveResource::Base  
self.site = “[http://localhost:3000](http://localhost:3000)”  
end

foo = Foo.find(2) # performs GET /foo/2.xml  
foos = Foo.find(:all) # performs GET /foo.xml

But this doesn’t re-use _any_ of ActiveRecord. Whilst the interface is  
similar in some ways, the underlying operations are very different.

ActiveRecord is very much a wrapper around a SQL database. Almost all  
the  
operations you can perform ultimately get translated into calls on the  
database connection for SELECT, UPDATE etc.

The other useful bits of ActiveRecord, like validations, are already  
mixins  
in their own right. That is, they come pre-mixed into  
ActiveRecord::Base,  
but you could mix them into your own class independently.

Regards,

Brian.

---

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**Author:** ![bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/977dab/32.png) [@bernd](https://www.ruby-forum.com/u/bernd)\
**Post date:** [May 11, 2007, 5:18pm UTC](https://www.ruby-forum.com/t/is-there-a-possibility-to-include-methods-of-a-class/103906/9 "2007-05-11T17:18:45Z")

</div>

On 11 May 2007, at 17:14, Brian C. wrote:

> > I do not want to change) and I want the methods of  
> > …  
> > … more stuff  
> > calls to @db,  
> > some to @lib, or (the best news) can combine behaviours from both in  
> > whichever way it likes.

That would actually be a so called Bridge Design Pattern… I like it  
I think I will use it for Ruby Patterns 😉

Thanks Brian!