From: Stefano Crocco <stefano.crocco@...>
Date: 2008-02-10T22:08:35+09:00
Subject: Re: Private encapsulation question

Alle Sunday 10 February 2008, andrea ha scritto:
> Hello,
> I am trying to improve my understanding of encapsulation but I can't
> understand the reason why the last 2 method calls in the following code
> produce different results (cut and paste in irb, plus return key):
>
> class N
>   def initialize(n)
>     @number=n
>   end
>
>   def self_n_wrapper
>     self.n
>   end
>
>   def n_wrapper
>      n
>   end
>
> private
>
>   def n
>     @number
>   end
>
> end
>
> a=N.new(8)
> a.n_wrapper
> a.self_n_wrapper
>
>
> Thanks for help
> Andrea

Ruby implements private methods forbidding to call them with an explicit 
receiver, but only with the explicit receiver, self. This is enough to ensure 
a private instance method of class A can't be called by, for example an 
instance method of class B, because in the latter self is an instance of class 
B, not of class A. For a similar reason, you can call that method from an 
instance method of a class C derived from A. A side effect of this approach is 
that you can't call a private method using the explicit receiver self, even if 

self.my_method

is the same as

my_method

I hope this helps

Stefano