# Array API

**URL:** <https://www.ruby-forum.com/t/array-api/146238>\
**Category:** Ruby\
**Created:** [August 19, 2008, 11:10am UTC](https://www.ruby-forum.com/t/array-api/146238 "2008-08-19T11:10:09Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![gandhi-tush](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/5daacb/32.png) [@gandhi-tush](https://www.ruby-forum.com/u/gandhi-tush)\
**Post date:** [August 19, 2008, 11:10am UTC](https://www.ruby-forum.com/t/array-api/146238/1 "2008-08-19T11:10:09Z")

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Hi,  
I am going through the ruby Array API. In the API , there is staetment

Included Modules  
Enumerable

Is this means that we are inheriting the enumerable class to array?

Also there is sort\_by method for the enumerable object, but I am able to  
use this method for array of object.

I have this type of array of Object:-  
[#\<UserDemo:0x89a5bd4 @attributes={“email3”=\>nil, “lastname”=\>“aikhe”,  
“firstname”=\>“mita”, “id”=\>“1”}\>,#\<UserDemo:0x89a5bd4  
@attributes={“email3”=\>nil, “lastname”=\>“aikhe”, “firstname”=\>“na”,  
“id”=\>“2”}\>]

How it is possible that we are able to use enumerable sort\_by method for  
an array of object?

Thanks & Regards,  
Tushar

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**Author:** ![gandhi-tush](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/5daacb/32.png) [@gandhi-tush](https://www.ruby-forum.com/u/gandhi-tush)\
**Post date:** [August 19, 2008, 11:49am UTC](https://www.ruby-forum.com/t/array-api/146238/2 "2008-08-19T11:49:02Z")

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On 19 Aug 2008, at 10:06, Tushar G. wrote:

> Hi,  
> I am going through the ruby Array API. In the API , there is  
> staetment
> 
> Included Modules  
> Enumerable
> 
> Is this means that we are inheriting the enumerable class to array?

Not inheriting. That means the Enumerable module is mixed in to Array  
(and similarly to Hash and other collections)

> How it is possible that we are able to use enumerable sort\_by method  
> for  
> an array of object?

Because that’s what including a module does: it adds the methods  
defined in the module to the class.

Fred

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**Author:** ![gandhi-tush](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/5daacb/32.png) [@gandhi-tush](https://www.ruby-forum.com/u/gandhi-tush)\
**Post date:** [August 19, 2008, 12:18pm UTC](https://www.ruby-forum.com/t/array-api/146238/3 "2008-08-19T12:18:43Z")

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Frederick C. wrote:

> On 19 Aug 2008, at 10:06, Tushar G. wrote:
> 
> > Hi,  
> > I am going through the ruby Array API. In the API , there is  
> > staetment
> > 
> > Included Modules  
> > Enumerable
> > 
> > Is this means that we are inheriting the enumerable class to array?
> 
> Not inheriting. That means the Enumerable module is mixed in to Array  
> (and similarly to Hash and other collections)
> 
> > How it is possible that we are able to use enumerable sort\_by method  
> > for  
> > an array of object?
> 
> Because that’s what including a module does: it adds the methods  
> defined in the module to the class.
> 
> Fred

Hi,  
Is sort\_by method will cause performance problem? or Is it faster  
sort?

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**Author:** ![gandhi-tush](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/5daacb/32.png) [@gandhi-tush](https://www.ruby-forum.com/u/gandhi-tush)\
**Post date:** [August 19, 2008, 2:41pm UTC](https://www.ruby-forum.com/t/array-api/146238/4 "2008-08-19T14:41:04Z")

</div>

On Tue, Aug 19, 2008 at 12:15 PM, Tushar G.  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Hi,  
> Is sort\_by method will cause performance problem? or Is it faster  
> sort?

The theoretical performance comparison between sort and sort\_by is  
explained here:

[http://www.ruby-doc.org/core/classes/Enumerable.html#M003151](http://www.ruby-doc.org/core/classes/Enumerable.html#M003151)

Nevertheless, when talking about performance it’s better to benchmark  
yourself for your  
specific case.

It basically all boils down to how expensive is to calculate the  
comparison of two keys in the array,  
versus the number of comparisons needed.

Jesus.

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**Author:** ![gandhi-tush](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/5daacb/32.png) [@gandhi-tush](https://www.ruby-forum.com/u/gandhi-tush)\
**Post date:** [August 19, 2008, 4:13pm UTC](https://www.ruby-forum.com/t/array-api/146238/5 "2008-08-19T16:13:22Z")

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2008/8/19 Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> > 
> 
> Not inheriting. That means the Enumerable module is mixed in to Array (and  
> similarly to Hash and other collections)

Actually, it is a form of multiple inheritance.

irb(main):001:0\> Array.ancestors  
=\> [Array, Enumerable, Object, Kernel]

> > an array of object?
> 
> Because that’s what including a module does: it adds the methods defined in  
> the module to the class.

This is only true in a very general sense, i.e. if you want to express  
with this that you can invoke methods defined in a module on an  
instance of a class that directly or indirectly (!) inherits the  
module.

irb(main):002:0\> Array.instance\_method :sort\_by  
=\> #\<UnboundMethod: Array(Enumerable)#sort\_by\>  
irb(main):003:0\> Array.instance\_method :size  
=\> #\<UnboundMethod: Array#size\>

Note the difference between #sort\_by (defined in Enumerable) and #size  
(defined in Array).

Rather the module is inserted into the lookup path (see output of  
#ancestors above). Otherwise methods from different modules could not  
invoke each other via super but instead one would overwrite the other:

irb(main):004:0\> class Base; def x; puts “base”; end; end  
=\> nil  
irb(main):005:0\> module A; def x;puts “mod a”; super; end; end  
=\> nil  
irb(main):006:0\> module B; def x;puts “mod b”; super; end; end  
=\> nil  
irb(main):007:0\> class D1 \< Base; include A; include B; end  
=\> D1  
irb(main):008:0\> class D2 \< Base; include B; include A; end  
=\> D2  
irb(main):009:0\> D1.new.x  
mod b  
mod a  
base  
=\> nil  
irb(main):010:0\> D2.new.x  
mod a  
mod b  
base  
=\> nil  
irb(main):011:0\> D1.ancestors  
=\> [D1, B, A, Base, Object, Kernel]  
irb(main):012:0\> D2.ancestors  
=\> [D2, A, B, Base, Object, Kernel]

Kind regards

robert

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**Author:** ![gandhi-tush](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/5daacb/32.png) [@gandhi-tush](https://www.ruby-forum.com/u/gandhi-tush)\
**Post date:** [August 19, 2008, 5:16pm UTC](https://www.ruby-forum.com/t/array-api/146238/6 "2008-08-19T17:16:40Z")

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On 19 Aug 2008, at 15:09, Robert K. wrote:

> with this that you can invoke methods defined in a module on an
> 
> Rather the module is inserted into the lookup path (see output of  
> #ancestors above). Otherwise methods from different modules could not  
> invoke each other via super but instead one would overwrite the other:

Of course. it would also mean that adding methods to a module after it  
had been included wouldn’t work.

Fred

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**Author:** ![gandhi-tush](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/5daacb/32.png) [@gandhi-tush](https://www.ruby-forum.com/u/gandhi-tush)\
**Post date:** [August 19, 2008, 6:45pm UTC](https://www.ruby-forum.com/t/array-api/146238/7 "2008-08-19T18:45:58Z")

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On 19 Aug 2008, at 11:15, Tushar G. wrote:

> Hi,  
> Is sort\_by method will cause performance problem? or Is it faster  
> sort?

It’s what is often known as a schwartzian transform.  
Joss Susser wrote some stuff up on sort/sort\_by just a few days ago:  
[http://blog.hasmanythrough.com/2008/8/17/sorting-things-out](http://blog.hasmanythrough.com/2008/8/17/sorting-things-out)

Fred