Re: Constructing an object

["Randy Brukardt" <randy@rrsoftware.com>]

"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message
news:wccirwi30q7.fsf@shell01.TheWorld.com...
...
> The Common Lisp Object System has such a feature.  You can declare
> methods that are called in addition to the parent's version (either
> before or after) rather than the more common feature of calling them
> instead of the parent's version.  And I think there's a feature for
> declaring a method that must call the parent's version somewhere within
> it -- or something like that.
>
> If such additional complexity were to be added to Ada (I doubt it!),
> it would be a shame to make it work just for Initialize/Finalize.
> It really should be a general purpose feature.  This need (where an
> overriding "should" call the parent) comes up a lot in OO code;
> Finalize is just a special case.

Yes, of course it should work everywhere. Finalize routines were just an
example of a routine that needs it.

Actually, it wouldn't be that hard to add that to Ada 200Y. We have the
"overriding" keyword to specify overriding. Additional keywords could
specify other types of extension -- "extends" perhaps. That would look like:

    extends
    procedure Finalize (Obj : in out My_Type);

or perhaps

    extends after
    procedure Finalize (Obj : in out My_Type);

to specify when the parent routine is called.

But I think that we'd only want to support calling the parent routine first
or last; special syntax for calling it in the middle hardly seems worth it
(and getting the parameters right then would be messy - calling the parent
last could be done with jumps, and first probably also could be done with
shared code).

I'm mildly sorry I didn't think of this when we were working on "overrides";
its a rather natural extension to the idea that also helps to prevent bugs.

                         Randy.