From: Minkoo Seo <minkoo.seo@...>
Date: 2006-02-15T01:08:30+09:00
Subject: Re: Private methods - only available to oneself?

gwtmp01@mac.com wrote:
> On Feb 13, 2006, at 7:08 PM, Adam P. Jenkins wrote:
> > I wasn't aware of singleton *methods*.  I thought there were
> > singleton *classes*, in which case the C++/Java definition of
> > private would do just as well, since a particular object would be
> > the only instance of the singleton class. That is:
>
> Well singleton methods are implemented by tucking them away in a
> singleton class
> but you don't have to know about that implementation to utilize the
> facility:
>
> a = [1,2,3,4]
> b = [5,6,7,8]
>
> def a.sum
>    inject(0) { |s, x| s + x }
> end
>
> a.sum	# -> 10
> b.sum	# NoMethodError exception
>
>
> I think this all might come into play when you consider 'class
> methods'.  In Ruby, classes are
> objects and so class methods are really singleton methods associated
> with a particular instance
> of Class.   If you didn't have Ruby's concept of private then any
> class method could directly
> call any other class method (because all classes are instances of
> Class).

I believe that the class method is implemented transparently in Ruby,
because we do not have to metion 'private' to make a certain class
method. Of course, it surely make sense that the class method could not
be impelemented without the notion of private. However, I think class
method example is not a thorough argument for private.

I'm afraid that I still do not follow the line of reasoning. Well, this
might be the result of my heavily java/c++ based way of thinking. I
also do not see any other reason for using private when I code some
programs (not the ruby itself). Why should a certain instance hide
itself from the other instances of the same class? Could anyone give me
an exmple?

Best,
Minkoo Seo