From: Kent Dahl <kentda@...>
Date: 2003-02-13T04:25:05+09:00
Subject: Re: inheriting from base classes

Gavin Sinclair wrote:
> I've stated enough times that inheriting from generic classes without
> preserving that generality is bad (IMO), e.g.
> 
>    class OrderedHash < Hash               # good
> 
>    class AssignmentResults < Hash         # bad
> 
> And one reason is that you are not putting enough effort into what
> methods are available to the users of your class.
> 
> So my previous post about the badness of too many methods is
> consistent with my point of view on this whole thread.

No such thing as too many methods, just a thing as too many accessible
methods. :-)

I can't think it is too difficult to make every method protected when
subclassing and then opening only up those methods that are actually
needed by the outside world.

 class Module
   def major_inheritance_lockdown
     puts "Lock 'er down tight!"
     superclass.instance_methods.each{|meth|
       protected meth
     }
   end
 end

 class AssignmentResults < Hash
   major_inheritance_lockdown
   public :each, :[] #etc
 end
 
 a = AssignmentResults.new
 a[5]=2 #=>toomanymethods.rb:17: protected method `[]=' called for
{}:AssignmentResults (NameError)

I'd plug all the holes and loose ends, but I've got a pizza is in the
oven. 

[insert DuckTyping argument that goes pro this kind of madness here]

In practice, I use SimpleDelegator a lot in this kind of situations, but
I'm somewhat worried about performance with it.

-- 
(\[ Kent Dahl ]/)_    _~_    __[ http://www.stud.ntnu.no/~kentda/ ]___/~
 ))\_student_/((  \__d L b__/  NTNU - graduate engineering - 5. year  )
( \__\_�|�_/__/ ) _)Industrial economics and technological management(
 \____/_�_\____/ (____engineering.discipline_=_Computer::Technology___)