From: James Edward Gray II <james@...>
Date: 2009-11-15T05:36:03+09:00
Subject: Re: Naming conventions -- was: Re: DRYing a Regex

On Nov 14, 2009, at 1:40 PM, Marnen Laibow-Koser wrote:

> But why is it worth extending an object instead of subclassing it?
> 
> In other words,
> class SpecialString < String
>  def method_I_need_once_or_twice
>  ...
> end
> ...
> @some_string = SpecialString.new(@some_string)
> 
> seems to me like the right way to do this -- you can check if a given 
> String instance is a SpecialString or a plain String, or simply use 
> overriding and polymorphism for delegation.

If you mix a module into the String, you can still use is_a?() to check for that module.  It can also override methods.  The object is still polymorphic.  I'm not understanding the advantages you think we are losing.

> Yet, if I understand you correctly, you and James are claiming that it 
> is preferable to do
> class << @some_string
>  def method_I_need_once_or_twice
> end
> 
> Do I understand correctly?

I would much prefer to mix a module into the object.  It has all the advantages of changing a singleton class, but it participates in the type system, can be read by RDoc, etc.

> If so, why?

Hopefully I've made my case by now, but just to sum it up one more time:  I think it's more flexible than subclassing, it does participate in the type system, it can be documented.  I'm not seeing the minuses.

James Edward Gray II