Re: Self pointer in limited record

[Georg Bauhaus <rm.tsoh+bauhaus@maps.futureapps.de>]

On Mon, 2007-09-03 at 21:17 +0200, Dmitry A. Kazakov wrote:
> On Mon, 03 Sep 2007 17:55:33 +0200, Jean-Pierre Rosen wrote:
> 
> > Dmitry A. Kazakov a écrit :
> >> It is difficult to see how an abstract state machine is not a type. The
> >> very word abstract assumes generalization, reuse and instances. It is types
> >> and generics, the tools to express the idea of instances.
> >> 
> > Sorry, but I beg to disagree here.
> > 
> > Abstraction is about the reduction of a real world objet to those 
> > elements that are relevant for a given point of view.
> 
> Of just one object? I think that an abstraction always apply to a set of
> things. What could be an abstraction of Spike, the dog?

(Hope you don't mind be stepping in here.)

The abstraction could be: Those elements of Spike that are relevant
for the given point of view on Spike? (Guiding the abstraction process.)
If you insist that abstraction as a word can only have the
meaning "common to many things" and that what a Spike
package will really do is a reduction of informational detail,
well, apparently there are different frames of reference for
"abstraction".

I wonder, though, why then we can still talk about abstract data
type and abstract state machine.


> > A singleton is an abstraction of a single object, and does not need a 
> > type. I don't see anything in the word abstract that assumes generalization.
> 
> There is little abstraction in being alone. This is actually the reason why
> no type is need for a singleton: no abstraction, no instances, no type.

Is there little abstraction in being alone (hm, who said that being
along is the source of the thing being an abstract?)
or is there no abstraction?

> In my view an abstract state machine has nothing to do with singletons. A
> state machine might be a singleton, per chance.

Could you say what you mean by "having nothing to do with"?
(Sorry for being pedantic, but I think "nothing" and "per
chance" (=something) differ.)

>  But an *abstract* state
> machine is definitely a type that generalizes many concrete state machines.

By what definition of type is an ASM a type that generalizes many
concrete state machines (=what, in Ada terms?)?