From: Ryan Davis <ryand-ruby@...>
Date: 2008-02-13T17:51:33+09:00
Subject: Re: @var = change to accessor method? Why?


On Feb 12, 2008, at 8:50 PM, Philipp Hofmann wrote:

> accessors are meant to make the instance variables of an object to be
> accessible from outside. creating accessors for every variable used in
> an object (in order to get rid of @s) makes every variable accessible
> from outside the object. therefore the data is not encapsulated any
> more.

I'm afraid you're confusing encapsulation with information hiding [0],  
especially as it pertains to inheritance. Both are good tools when  
used in the right context, but they are not the same. You do not  
"break" your code every time you use one of the attr generator  
methods. Instead you provide an interface to some information that  
your class/instance provides. You're not opening a vault and letting  
everything run crazy/chaotic by providing access to those instance  
variables. Instead, you're providing a clean and orderly way of  
getting at that data[1].

Providing accessor methods is the only sane way to make your code and  
its subclasses more resilient to change. It allows you to change the  
internals without affecting the subclasses that use that interface.  
Classes that use ivars directly are more brittle and require more work  
to maintain.

 From Beck's Smalltalk Best Practices:

> If you need to code for inheritance, use Indirect Variable Access.  
> Future generations will thank you.
>
> One warning--do not go half way. If you are going to use direct  
> access, use it for all access.

[0] http://c2.com/cgi/wiki?EncapsulationIsNotInformationHiding
[1] As I've said before, if it is anywhere in ruby and evaled or  
parsed in any way, I can get my hands on it and manipulate it. If that  
scares or bothers you, you're using the wrong language.