From: Brian Candler <b.candler@...>
Date: 2009-06-07T01:54:21+09:00
Subject: Re: code organization

Li Chen wrote:
> What are the differences bewteen the following code organization?
> What situations are preferred by each one?

In code 1, module A is just acting as a namespace, so that you have two 
classes, A::B and A::C. This is useful to ensure that your class names 
don't stomp on anyone else's use of the same names. All you have to do 
is ensure name A is unique.

Code 2 doesn't run as it stands, so you need to rewrite as:

module A; end

class B
   include module A
end

class C
  include module A
end

In this case, instance methods defined in module A are available in both 
class B and class C. This is almost the same as subclassing B and C from 
class A. B and C also get access to any constants defined in the A 
namespace, without needing the A:: prefix.

So in summary: they achieve two completely different ends (namespace 
separation, and method sharing, respectively)
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