From: Dave Thomas <Dave@...>
Date: 2003-08-17T03:48:45+09:00
Subject: Re: Newbie Q: Data encapsulation with Ruby


On Saturday, August 16, 2003, at 12:31 PM, Meino Christian Cramer wrote:
>   Until this point I thought, "attributes" _are_ instance variables...
>   (haveing C++ in mind...)
>
Attributes are methods which give you access to instance variables. As 
others have said, they are the quivalent of Java's getters and setters.

    attr_reader :fred

is the same as writing

   def fred
     @fred
   end

Ruby is good this way: objects can choose to expose their state 
directly, but then they can change to having more complex method-based 
access. The key thing is that this change is transparent to users of 
the object: when you say

   f.age

you have no idea if you're getting the age as a transparent reference 
to an instance variable or as the result of some computation. Read 
Meyer's Object Oriented Software Construction for a lot of information 
on this - he calls it the Uniform Access Principle, and it's one way of 
increasing encapsulation and decreasing coupling.


Cheers


Dave