# Properly using Ruby's specialness

**URL:** <https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371>\
**Category:** Ruby\
**Created:** [January 17, 2008, 8:04pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371 "2008-01-17T20:04:33Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![nefigah](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e47774/32.png) [@nefigah](https://www.ruby-forum.com/u/nefigah)\
**Post date:** [January 17, 2008, 8:04pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371/1 "2008-01-17T20:04:33Z")

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I was recently reading a presentation on “10 things Java programmers  
should know about Ruby.” Like many similar discourses, it talked about  
classes being objects and singleton methods etc. etc. Now, I am familiar  
with these different things, but I think I am too stupid to discern  
their inherent worth.

1. Open classes. The other day, in a little Blackjack game I wrote in  
Ruby, I used this feature to add in a method to the Array class instead  
of making a class that inherited from Array and added that method.  
However, a) I’m not sure if that was the “right” way and b) I’m not sure  
if there is an advantage to that approach over the latter, per se.

2. Singleton methods. I really can’t think of a particular example where  
I would use this… please help!

3. Blocks. Although now (after some practice and getting used to) these  
make sense to me when I use them with methods already designed, I don’t  
think I have internalized them to the point where I would write my own  
methods that accepted them and worked with them. Has anyone else been in  
the same boat, or do they usually just “click”?

Thank you and sorry for the noobness,

J

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<div class="post-metadata">

**Author:** ![nefigah](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e47774/32.png) [@nefigah](https://www.ruby-forum.com/u/nefigah)\
**Post date:** [January 17, 2008, 9:15pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371/2 "2008-01-17T21:15:41Z")

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On Jan 17, 2008, at 1:04 PM, J. Cooper wrote:

> 1. Open classes. The other day, in a little Blackjack game I wrote in  
> Ruby, I used this feature to add in a method to the Array class  
> instead  
> of making a class that inherited from Array and added that method.  
> However, a) I’m not sure if that was the “right” way and b) I’m not  
> sure  
> if there is an advantage to that approach over the latter, per se.

Open classes are best used sparingly. There are problems with them,  
of course, in that your code might collide with someone else’s code.  
The plus though is that all instances of the changed class are  
suddenly empowered with new methods you can count on. Some good uses,  
in my opinion, are:

- Conversion methods – I would rather type %w[a b c].to\_csv than  
CSV.generate\_line(%w[a b c]. I don’t feel there’s much danger of  
namespace collision here either due to the specific types in the  
method names. Some disagree and feel this is polluting the namespace  
though.
- DSL – It can often be convenient to make Ruby understand the  
language of your problem rather than to express your problem in Ruby.

> 1. Singleton methods. I really can’t think of a particular example  
> where  
> I would use this… please help!

Well, technically you use this feature in Ruby anytime you create a  
class method. Outside of that, it’s another feature best used in  
moderation. It does have interesting possibilities though. Here’s an  
example to try and get you thinking in new directions:

> > def add\_counts(array)  
> > counts = array.inject(Hash.new(0)) { |c, e| c.merge(e =\> c[e] +

1. }

> > class \<\< array; self; end.send(:define\_method, :counts) do  
> > ?\> counts  
> > end  
> > end  
> > =\> nil  
> > a = Array.new(10) { rand(6) }  
> > =\> [2, 3, 3, 3, 0, 2, 4, 3, 4, 3]  
> > add\_counts(a)  
> > =\> #Proc:0x0059dc60@:11(irb)  
> > a.counts  
> > =\> {0=\>1, 2=\>2, 3=\>5, 4=\>2}

> 1. Blocks. Although now (after some practice and getting used to)  
> these  
> make sense to me when I use them with methods already designed, I  
> don’t  
> think I have internalized them to the point where I would write my own  
> methods that accepted them and worked with them. Has anyone else  
> been in  
> the same boat, or do they usually just “click”?

I wrote about this on my blog a while back. Maybe it will help:

[http://blog.grayproductions.net/articles/code\_as\_a\_data\_type](http://blog.grayproductions.net/articles/code_as_a_data_type)

James Edward G. II

James Edward G. II

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<div class="post-metadata">

**Author:** ![nefigah](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e47774/32.png) [@nefigah](https://www.ruby-forum.com/u/nefigah)\
**Post date:** [January 17, 2008, 8:36pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371/3 "2008-01-17T20:36:30Z")

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J. Cooper wrote:

> if there is an advantage to that approach over the latter, per se.  
> Thank you and sorry for the noobness,  
> It seems like you want to read the book “Design Patterns in Ruby”. It  
> goes into great detail when to use what, and why, and such stuff.

Best regards,

Jari W.

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<div class="post-metadata">

**Author:** ![nefigah](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e47774/32.png) [@nefigah](https://www.ruby-forum.com/u/nefigah)\
**Post date:** [January 17, 2008, 9:59pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371/4 "2008-01-17T21:59:58Z")

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On Jan 17, 2008, at 2:04 PM, J. Cooper wrote:

> of making a class that inherited from Array and added that method.  
> However, a) I’m not sure if that was the “right” way and b) I’m not  
> sure  
> if there is an advantage to that approach over the latter, per se.

That was the correct way to do it! The advantage is you can  
instantiate an array object like normal ([]), instead of having to do  
MyArray.new(3, 4, 5)

> 1. Singleton methods. I really can’t think of a particular example  
> where  
> I would use this… please help!

When you would need to add a method into a class, or create a  
subclass with a special method BUT the method is only used by one  
object (IE, only one instantiation of MyArray).

Also, you should use it when you want methods to be called within a  
class but outside of a method definition.

> 1. Blocks. Although now (after some practice and getting used to)  
> these  
> make sense to me when I use them with methods already designed, I  
> don’t  
> think I have internalized them to the point where I would write my own  
> methods that accepted them and worked with them. Has anyone else  
> been in  
> the same boat, or do they usually just “click”?

They typically just click 🙂

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<div class="post-metadata">

**Author:** ![nefigah](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e47774/32.png) [@nefigah](https://www.ruby-forum.com/u/nefigah)\
**Post date:** [January 17, 2008, 10:03pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371/5 "2008-01-17T22:03:34Z")

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On 1/17/08, James G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Open classes are best used sparingly. There are problems with them,  
> of course, in that your code might collide with someone else’s code.  
> The plus though is that all instances of the changed class are  
> suddenly empowered with new methods you can count on. Some good uses,  
> in my opinion, are:
> 
> - Conversion methods
> - DSL

I think that rather than sparingly, the adverb should be carefully.

Open classes are very powerful in situations like building a  
framework, (e.g. Rails). Features such as plugins, use formalized  
patterns of extending open classes to allow opening classes while  
minimizing the potential for collisions.

> > > counts = array.inject(Hash.new(0)) { |c, e| c.merge(e =\> c[e] +
> 
> 1. }
> 
> > > class \<\< array; self; end.send(:define\_method, :counts) do  
> > > ?\> counts  
> > > end  
> > > end

Right, another is to accomplish what the OP did by adding an instance  
to Array in a safer more controlled fashion. Rather than “duck  
punching” all now and future instance of Array we can specialize  
particular instances.

> [http://blog.grayproductions.net/articles/code\_as\_a\_data\_type](http://blog.grayproductions.net/articles/code_as_a_data_type)

–  
Rick DeNatale

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

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<div class="post-metadata">

**Author:** ![nefigah](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e47774/32.png) [@nefigah](https://www.ruby-forum.com/u/nefigah)\
**Post date:** [January 17, 2008, 11:35pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371/6 "2008-01-17T23:35:45Z")

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Hmm… yeah, I think I may literally be too dumb for Ruby. I guess I  
just can’t get my head around the dynamicness. ☹

Thanks for the replies

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**Author:** ![nefigah](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e47774/32.png) [@nefigah](https://www.ruby-forum.com/u/nefigah)\
**Post date:** [January 17, 2008, 10:11pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371/7 "2008-01-17T22:11:15Z")

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On Jan 17, 2008, at 3:02 PM, Rick DeNatale wrote:

> > > if there is an advantage to that approach over the latter, per se.
> 
> I think that rather than sparingly, the adverb should be carefully.
> 
> Open classes are very powerful in situations like building a  
> framework, (e.g. Rails). Features such as plugins, use formalized  
> patterns of extending open classes to allow opening classes while  
> minimizing the potential for collisions.

In an example in Practical Ruby Projects, the author has to load some  
some operating specific code. He feels that open classes are great  
for that. He codes up the general interface of the class and then  
insert the other methods tailored to the operating system later.

This does seem to come out smoother than having to deal with a bunch  
of specific subclasses. The unneeded code is just not added in.

James Edward G. II

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**Author:** ![nefigah](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e47774/32.png) [@nefigah](https://www.ruby-forum.com/u/nefigah)\
**Post date:** [January 17, 2008, 10:33pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371/8 "2008-01-17T22:33:19Z")

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On Jan 17, 2008 10:10 PM, James G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> In an example in Practical Ruby Projects, the author has to load some  
> some operating specific code. He feels that open classes are great  
> for that. He codes up the general interface of the class and then  
> insert the other methods tailored to the operating system later.
> 
> This does seem to come out smoother than having to deal with a bunch  
> of specific subclasses. The unneeded code is just not added in.  
> There is almost no Ruby quiz solution I have ever submitted that does  
> not do that, it feels somehow like, look Ruby I know better than you  
> do though 😉
> 
> James Edward G. II

–  
[http://ruby-smalltalk.blogspot.com/](http://ruby-smalltalk.blogspot.com/)

* * *

Whereof one cannot speak, thereof one must be silent.  
Ludwig Wittgenstein

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**Author:** ![nefigah](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/e47774/32.png) [@nefigah](https://www.ruby-forum.com/u/nefigah)\
**Post date:** [January 18, 2008, 7:33pm UTC](https://www.ruby-forum.com/t/properly-using-rubys-specialness/126371/9 "2008-01-18T19:33:40Z")

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My personal rule of thumb is, that when something “appears” logical and  
straightforward, I use it.

And if i have had bad experience with it in the past, I dont use that  
feature.  
In the end I use only a subset of Ruby (but it makes me happy because it  
is a lot more elegant than any other language I know of).