Re: Self pointer in limited record

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 06 Sep 2007 13:53:50 +0200, Jean-Pierre Rosen wrote:

> Dmitry A. Kazakov a �crit :
>> You don't need to model Spike's weight in your system because changing the
>> weight should have no effect. Spike cannot communicate its weight to other
>> components of the system, because it is not *a* thing with mass. No, it is
>> just Spike, the One. Its weight has been abstracted away.
> Sorry, but I'm really puzzled at this point.
> What do you know about *my* system?
> 
> You seem to be of the kind of people who classify everything (no attack 
> intended: just an observation). In my experience, about half of the 
> people (but only half) think this way: if it has a weight, it must 
> belong to the class of massive things. The rest of the world (to whom I 
> belong) view things as having properties without the need of 
> classifying. Maybe it is a matter of being left- or right-brained...

Hmm, I think you mean here constructive vs. non-constructive sets, like {x
| P(x)}, where P is some predicate, like "has weight." But in finite case
and a properly typed system everything is constructive anyway. I can always
determine if the given object has mass. No difference.

>> Weight is a number with all properties of real values + ones of mass,
>> acceleration etc. But Spike's weight (tm) is not a number. It is another
>> singleton specific to Spike and unrelated to anything else = nothing.

> Spike's weight is a physical property, but its abstraction (i.e. what I 
> need from weight in my application) is its value in measurement unit.

Yes, this is what I meant. Weight here is abstracted from Spike. When you
get its value, that does not remember Spike. You have an operation that
acts on Spike and yields weight. It is X.Weight or X'Weight or Weight(X),
whatever, where X is Spike. But X here can be something different from
Spike. You can measure something *else*. Spike is not a singleton for this
operation.

> BTW, I would not say it is a singleton. Weight is not an object at all, 
> it is a simple value. Remember: not everything is an object (I hope 
> Michel Gauthier reads this)

I called it singleton in order to distinguish the case when weight were not
abstracted from Spike. In that case you would not need to model it, Spike
and Spike's weight were just equivalent.

P.S. Yes, value is not an object, it is a state of.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de