From: Mark Wilson <mwilson13@...>
Date: 2003-08-17T04:22:31+09:00
Subject: Re: Newbie Q: Data encapsulation with Ruby


On Saturday, August 16, 2003, at 01:31 PM, Meino Christian Cramer wrote:

> [snip]

> The whole attr_* family of methods really just saves some typing.
>
>   ...but for me it would break down all "walls" and access controls a
>   class would (should?) have over its instance variables...
>
>   Doesn't such a design tend to become more "procedural" (in opposite
>   to OOP) than wanted?
> [snip]

Hello Meino,

I think you're raising a question about what OOP really is, 
particularly when source code is open.

There are some objects that hold information that is used by other 
objects. You want these objects to provide that information when 
another object asks for it. This is the method attr_reader provides. 
Sometimes you want an object to permit other objects to update 
information being held by that object. This is the method attr_writer 
provides. You can use one or the other or both or neither. Some objects 
have no methods permitting access to the information they hold -- this 
kind of object does something in response to a method call by another 
object, but does not give or receive information that it contains.

As the programmer, you see the object from the inside and the outside. 
If you use test-driven development, you start by looking at the object 
from the outside and give it methods that will respond as desired when 
called -- you are focusing on the interface to the object. Once you 
write the test you then change your (conceptual) position and go inside 
the object and figure out how you can respond to the method. This often 
involves using some procedural code (although you can create objects of 
any available class inside the method as well).

Note that the above is all theory. There is no substitute for reading 
other people's code (check the files in your /lib/ruby/1.8/ directory) 
and writing your own code. One last note, in Ruby, you don't have to 
write your own classes and methods to write a functioning program -- 
you can use objects defined by classes and methods built in or added to 
Ruby by others and write programs entirely in the "main" object space.

Regards,

Mark