From: Robert Klemme <shortcutter@...>
Date: 2009-05-27T16:44:38+09:00
Subject: Re: Do you nest classes inside classes?

2009/5/26 Simon Chiang <simon.a.chiang@gmail.com>:
> I sometimes use nested classes to avoid namespace clutter.  The only
> downsides I found are related to inheritance, in particular when you
> split out classes into different files.
>
>  [a.rb]
>  require 'a/b'
>  class A < SuperClass
>  end
>
>  [a/b.rb]
>  class A < SuperClass
>    class B
>    end
>  end
>
> In both files you have to have the correct superclass (which can be
> hard during refactoring).  There are different ways to construct this,
> however:
>
>  [a.rb]
>  class A < SuperClass
>    require 'a/b'
>  end
>
>  [a/b.rb]
>  class A::B
>  end
>
> The downside of this is that 'a/b.rb' can't be required on it's own.

IMHO this is not a problem of inheritance but of clear priority: class
A should be defined in one primary file.  All other files that
*modify* it (i.e. by adding method or whatnot) should require that
primary file and reopen the class to do whatever they need.

So, basically the layout should look like this:

[a.rb]
class A < SuperClass
  def method_of_A_which_does_not_use_B
  end
end

[a/b.rb]
require 'a'

class A
  class B
  end

  def method_of_A_which_uses_B
  end
end

Actually, if you use A only for namespace handling then a module would
probably a better thing to have here.  Other than that, if A's
implementation needs A::B to work, then splitting both out into two
files does not make much sense.

Kind regards

robert


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