[DGD]Object Upgrading Scenario

[Felix A. Croes]

> From: "Jason Cone" <jcone at uscdev.com> wrote:

>[...]
> Anyway, let assume the following object relationships:
>
>     A -i-> B -i-> C -c-> D
>     A -i-> B -i-> C -i-> E -c-> F
>
> This notation should read, "Object D is a clone of object C which inherits
> B, which inherits A.  Object F is a clone of object E which inherits object
> C."
>
> Bad design issues aside, what is a possible implementation that could take
> object E into account?  If E (and, consequently, F) didn't exist, an
> overloaded compile_object() function would do the following:
>
>     destruct_object(A)
>     destruct_object(B)
>     ::compile_object(C)
>
> This would then allow for the single/multiple D object(s) to take advantage
> of the new functionality that was added to A.  That approach, however, would
> really mess things up if it used the same approach when trying to upgrade E
> (F) -- ::compile_object() could not be called on object C as E inherits C
> (would yield a run-time error).
>
> Thoughts?

There isn't any way to upgrade all existing objects in your scenario.
It is a special case of the more general problem:

    If an object is both inherited and used in any other way (either
    it has had a function called in it, or it has been cloned),
    upgrading both this object and those that inherit it is not
    possible.

This is precisely why I prevented using/cloning of inheritable objects
in the kernel library.


> I know this subject has been beaten to death, but since we're running across
> this issue during the implementation stage, my hope is that we can share a
> successful implementation with everyone and not just discuss it on a
> hypothetical issue.  I would like this scenario resolved, though, if
> possible. :)

With the existing primitive operations (compiling an object, recompiling
an object, destructing an object), upgrading of all objects is not
possible in your scenario.

By the way, the subject is far from beaten to death.  I rather think
it died prematurely. :)

Regards,
Dworkin

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