# Enumerating and mixin

**URL:** <https://www.ruby-forum.com/t/enumerating-and-mixin/177188>\
**Category:** Ruby\
**Created:** [October 13, 2009, 1:30am UTC](https://www.ruby-forum.com/t/enumerating-and-mixin/177188 "2009-10-13T01:30:34Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![Rajinder\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/91b2a8/32.png) [@Rajinder\_Y](https://www.ruby-forum.com/u/Rajinder_Y)\
**Post date:** [October 13, 2009, 1:30am UTC](https://www.ruby-forum.com/t/enumerating-and-mixin/177188/1 "2009-10-13T01:30:34Z")

</div>

I am trying to learn the correct way to enumerate in Ruby, a few things  
are  
missing in my 1st stab at this. How do I use mixin with Enumerable to  
rewrite  
the class I have below? I can’t seem to find a concrete example online?

I know I am also missing code to override \<=\> if I wanted to do sorting,  
are the  
other overrides I am missing?

How do I make my code more elegant, Thanks!

class Vowels  
def initialize  
@index = 0  
@list = %w(a e i o u)  
end

```
def each
   while( @index < @list.size )
      if @index >= @list.size
         yield nil
         exit
      else
         yield @list[@index]
         @index += 1
      end
   end
end

def first
   @index=0
end

```

end

obj = Vowels.new

obj.each { |x| puts x }

–  
Kind Regards,  
Rajinder Y.

[http://DevMentor.org](http://DevMentor.org)  
Do Good ~ Share Freely

---

<div class="post-metadata">

**Author:** ![Rajinder\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/91b2a8/32.png) [@Rajinder\_Y](https://www.ruby-forum.com/u/Rajinder_Y)\
**Post date:** [October 13, 2009, 1:48am UTC](https://www.ruby-forum.com/t/enumerating-and-mixin/177188/2 "2009-10-13T01:48:42Z")

</div>

Rajinder Y. wrote:

> ```
> exit
> 
> ```
> 
> end
> 
> obj = Vowels.new
> 
> obj.each { |x| puts x }

OK I managed to sweet the code down to the following, is there anything  
else I  
missed?

class Vowels  
include Enumerable  
def initialize  
@list = %w(u e a o i)  
end

```
def each
   @list.each { |item| yield item }
end

```

end

obj = Vowels.new

obj.each { |s| print s }  
puts “”  
obj.sort.each { |s| print s }  
puts “”

–  
Kind Regards,  
Rajinder Y.

[http://DevMentor.org](http://DevMentor.org)  
Do Good ~ Share Freely

---

<div class="post-metadata">

**Author:** ![Rajinder\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/91b2a8/32.png) [@Rajinder\_Y](https://www.ruby-forum.com/u/Rajinder_Y)\
**Post date:** [October 13, 2009, 9:10pm UTC](https://www.ruby-forum.com/t/enumerating-and-mixin/177188/3 "2009-10-13T21:10:41Z")

</div>

On 13.10.2009 01:47, Rajinder Y. wrote:

> ```
> @list.each { |item| yield item }
> end
> 
> ```
> 
> end
> 
> obj = Vowels.new
> 
> obj.each { |s| print s }  
> puts “”  
> obj.sort.each { |s| print s }  
> puts “”

Two notes: you can actually pass the block directly on to method each of  
Array.

def each(&b)  
@list.each(&b)  
end

And: conventionally #each returns self.

Taking both together you could do

def each(&b)  
@list.each(&b)  
self  
end

Kind regards

robert

---

<div class="post-metadata">

**Author:** ![Rajinder\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/91b2a8/32.png) [@Rajinder\_Y](https://www.ruby-forum.com/u/Rajinder_Y)\
**Post date:** [October 14, 2009, 4:29am UTC](https://www.ruby-forum.com/t/enumerating-and-mixin/177188/4 "2009-10-14T04:29:48Z")

</div>

Brian C. wrote:

> You mention \<=\>. This isn’t needed here because each of the elements you  
> yield is a String, and strings already have \<=\> and so the elements can  
> be sorted. But if you want a different exercise, try:

Brian thanks for the demonstration of how to use Comparable, and also  
pointing  
out the other methods that can be redefined. If you didn’t mention that,  
I would  
have stopped at \<=\>. Although I suspect the other methods make use of  
\<=\>  
internally?

> end
> 
> > > Comparable.instance\_methods  
> > > =\> [“==”, “\>=”, “\<”, “\<=”, “\>”, “between?”]
> 
> Regards,
> 
> Brian.

–  
Kind Regards,  
Rajinder Y.

[http://DevMentor.org](http://DevMentor.org)  
Do Good ~ Share Freely

---

<div class="post-metadata">

**Author:** ![Rajinder\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/91b2a8/32.png) [@Rajinder\_Y](https://www.ruby-forum.com/u/Rajinder_Y)\
**Post date:** [October 13, 2009, 10:41am UTC](https://www.ruby-forum.com/t/enumerating-and-mixin/177188/5 "2009-10-13T10:41:58Z")

</div>

Rajinder Y. wrote:

> OK I managed to sweet the code down to the following, is there anything  
> else I  
> missed?

That’s fine. So far your Vowels class doesn’t really do anything more  
than a simple Array would, but you’ve shown how your class gains methods  
from the Enumerable module, and you can now add extra functionality  
which is specific to a set of vowels. (This is composition by  
delegation, an approach I highly recommend)

You mention \<=\>. This isn’t needed here because each of the elements you  
yield is a String, and strings already have \<=\> and so the elements can  
be sorted. But if you want a different exercise, try:

class Vowel  
include Comparable  
def initialize(v)  
@v = v  
end  
def to\_s  
@v  
end  
def \<=\>(other)  
@v \<=\> other.to\_s  
end  
end

v1 = Vowel.new(“a”)  
v2 = Vowel.new(“e”)  
v1 \< v2 #=\> true  
v3 = Vowel.new(“e”)  
v2 == v3 #=\> true

Here you’re exercising a different mixin, Comparable. It takes any class  
which implements a \<=\> operator, and adds these methods for you:

> > Comparable.instance\_methods  
> > =\> ["==", “\>=”, “\<”, “\<=”, “\>”, “between?”]

Regards,

Brian.

---

<div class="post-metadata">

**Author:** ![Rajinder\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/91b2a8/32.png) [@Rajinder\_Y](https://www.ruby-forum.com/u/Rajinder_Y)\
**Post date:** [October 14, 2009, 9:59am UTC](https://www.ruby-forum.com/t/enumerating-and-mixin/177188/6 "2009-10-14T09:59:32Z")

</div>

Rajinder Y. wrote:

> Brian thanks for the demonstration of how to use Comparable, and also  
> pointing  
> out the other methods that can be redefined. If you didn’t mention that,  
> I would  
> have stopped at \<=\>. Although I suspect the other methods make use of  
> \<=\>  
> internally?

That’s exactly what Comparable does: these new methods in turn call the  
\<=\> method that you defined.

In the same way, Enumerable gives you a whole bunch of new methods,  
which in turn make use of ‘each’ (and only ‘each’). So as long as you  
have defined an ‘each’ method which yields the collection members in  
turn, all the other methods in Enumerable will work.

Regards,

Brian.

---

<div class="post-metadata">

**Author:** ![Rajinder\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/91b2a8/32.png) [@Rajinder\_Y](https://www.ruby-forum.com/u/Rajinder_Y)\
**Post date:** [October 14, 2009, 4:30am UTC](https://www.ruby-forum.com/t/enumerating-and-mixin/177188/7 "2009-10-14T04:30:58Z")

</div>

Robert K. wrote:

> > puts “”  
> > Taking both together you could do
> 
> def each(&b)  
> @list.each(&b)  
> self  
> end

Robert, I didn’t know method each should return self, learned something  
to add  
to my notes =), also seeing use of &b to denote a code-block drives home  
what  
I’ve been reading, thanks!

> Kind regards
> 
> ```
> robert
> 
> ```

–  
Kind Regards,  
Rajinder Y.

[http://DevMentor.org](http://DevMentor.org)  
Do Good ~ Share Freely

---

<div class="post-metadata">

**Author:** ![Rajinder\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/91b2a8/32.png) [@Rajinder\_Y](https://www.ruby-forum.com/u/Rajinder_Y)\
**Post date:** [October 14, 2009, 10:25am UTC](https://www.ruby-forum.com/t/enumerating-and-mixin/177188/8 "2009-10-14T10:25:07Z")

</div>

2009/10/14 Rajinder Y. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> > Enumerable module, and you can now add extra functionality which is specific  
> > use of \<=\> internally?  
> > Exactly - as Brian wrote. You can “see” this at work here:

09:45:55 ~$ ruby19 -e ‘class X;include Comparable;def \<=\>(o);0  
end;end;x=X.new;set\_trace\_func lambda {|\*a| p a};x\<x’  
[“c-return”, “-e”, 1, :set\_trace\_func, #Binding:0x100a4bb8, Kernel]  
[“line”, “-e”, 1, nil, #Binding:0x100a4a78, nil]  
[“c-call”, “-e”, 1, :\<, #Binding:0x100a499c, Comparable]  
[“call”, “-e”, 1, :\<=\>, #Binding:0x100a4898, X]  
[“line”, “-e”, 1, :\<=\>, #Binding:0x100a47a8, X]  
[“return”, “-e”, 1, :\<=\>, #Binding:0x100a46cc, X]  
[“c-return”, “-e”, 1, :\<, #Binding:0x1001d744, Comparable]  
09:46:07 ~$

> > Here you’re exercising a different mixin, Comparable. It takes any class  
> > which implements a \<=\> operator, and adds these methods for you:
> > 
> > > > Comparable.instance\_methods
> > 
> > =\> [“==”, “\>=”, “\<”, “\<=”, “\>”, “between?”]

Kind regards

robert