From: Marnen Laibow-Koser <marnen@...>
Date: 2009-11-15T04:40:18+09:00
Subject: Re: Naming conventions -- was: Re: DRYing a Regex

David A. Black wrote:
[...]
> I write class methods sometimes (I know those are singleton with an
> asterisk next to them, but still), 

Sometimes they're the right thing...

> and I think that extending core
> objects with modules is a frequently overlooked and very powerful
> alternative to reopening core classes and adding methods.
> 
> This kind of thing:
> 
>    class String
>      def method_I_need_once_or_twice
>      ...
> 
> is almost always overkill. It's sort of the core-functionality
> counterpart of using global variables. 

True.  (Even though I occasionally do this.)

> Extending an object is a much
> more precise operation -- and has the additional merit, I find, of
> really making you think about whether it's worth bothering to the
> extend the object instead of working with what the object can already
> do.
> 

Agreed.  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.

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?  If so, why?  I hesitate to contradict such 
experts as you and James, but I'm really not seeing the benefit.  For 
one thing, type-checking completely falls down with this pattern. 
Polymorphism may or may not, depending on how it's implemented.  And I 
don't see a single advantage that we get in return for the loss of 
type-checking.  What am I missing?

Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen@marnen.org
> 
> David
> 
> --
> The          Ruby training with D. Black, G. Brown, J.McAnally
> Compleat     Jan 22-23, 2010, Tampa, FL
> Rubyist      http://www.thecompleatrubyist.com
> 
> David A. Black/Ruby Power and Light, LLC (http://www.rubypal.com)

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