From: Dave Thomas <Dave@...>
Date: 2002-02-05T04:25:05+09:00
Subject: Re: Subclassing vs Subtyping (partly OOP vs FP)

Robert Feldt <feldt@ce.chalmers.se> writes:

> I guess there is no easy way out of the problem that you can't  
> semantically check methods unless you describe the semantics in a
> machine-understandable form. The good thing with describing the semantics
> is that we get an oracle that can be used for testing.

I think I was thinking about something less ambitious/. Say you have
out friend BagCollectable that implements bag functionality for some
container. BadCollectable relies on its host class implementing
methods #add, #remove, #includes? and #each, and exports a bunch of
cosmetic methods based on these. We have a set of implementations:

  class BTreeBag
    include BagCollectable
    ...
  end

  class ArrayBag
    include BagCollectable
    ...
  end

  class LinkedListBag
    include BagCollectable
    ...
  end

etc

Then we _could_ arrange it so that BagCollectable did some basic
checking if (say) the -d flag was set:

1. It could check that classes it was mixed in to defined the methods
   it needed.

2. It could generate some basic tests, exercising each class in to
   which it is mixed by calling their #add, #remove, etc methods


Then take it a step further, and break these tests out into a separate
module:

  class BTreeBag
    implements BagProtocol
    includes   BagCollectable

    ...
  end


Regards


Dave