From: stephenT <stiv.thomas@...>
Date: 2008-02-02T23:39:58+09:00
Subject: Re: Gedankenexperiment on method duck type safety

The first thing that comes to mind, and this may say more about the
oddities of my mind and lack of any real cs training, is that part of
what you want is, that once you've identified a duck you(or the
runtime system) want to 'know' about ducks. If you have another animal
you want to be able to:
  1. ask is this a duck - does it do the same things that the known
duck does?
  2. you may want to 'know' that this is also a duck - automatic
subclassing and extraction of commonalities.
  3. you may want to get a duck and do something with it (last time I
caught a duck a took it into a bar just to see what would happen)

I guess you could extend the base object to include a 'type manager'
to which you could add type identified instances and build,
dynamically, the meaning of a particular type from the instances. You
could also validate or test instances against your types - imagine
getting the response 90% confident that it's a duck, 60% confident
that it's a chicken, 1% dog.

Slightly askew of the point: In the run time context is it more
important to know if 'this' thing quacks and then get it to quack
(point to point message) or do you just need something(s) to quack
(broadcast message). Not more important in general, but this might be
an important questions to ask in the initial design.