Re: Constructing an object

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

On Fri, 30 Sep 2005 10:14:47 +0200, Jean-Pierre Rosen wrote:

> Randy Brukardt a �crit :
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
>>>They aren't extensible in the sense that you can only override or inherit.
>>>It is too dangerous for constructors and assignments. BTW, Ada does not to
>>>completely override them anyway. For example the parts responsible for
>>>initialization of the components cannot be overridden. One cannot have a
>>>task component which will not start because Initialize does not call the
>>>parent's one! (:-))
>> 
>> Ah, I see. Certainly you are right here. I see that a lot in Finalize
>> routines; it is real easy to forget to call the Finalize for the parent
>> type. There ought to be a better way of extending rather than replacing
>> routines; that's especially true since requires an explicit type conversion
>> to the parent to make that call, and it is easy to get wrong (and go
>> infinitely recursive).
>> 
> I think CLOS has such a feature, but it raises an issue:
> sometimes you want to call the parent Finalize *before* your own 
> Finalize, sometimes *after*. If it is automatic, you must force one of 
> them, which makes problems if you want the other one.

Yes, but I almost sure that this one is rooted in an incompleteness of the
construction model. If we consider T and T'Class as different types, then
we should consistently conclude that they might have constructors of their
own. (Of course T'Class destructor includes one of T.) I wonder if all
cases when one needs to call parent's Finalize out of order, are actually
ones which should be handled by the Finalize of T'Class. Now because
class-wide objects should be finalized before all specific ones, Finalize
of T'Class would be called before Finalize of any S derived from T. One
could even safely dispatch from it!

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