Re: GOOPS %modify-[instance|class]

[Mikael Djurfeldt <djurfeldt@nada.kth.se>]

Clinton Ebadi <clinton@unknownlamer.org> writes:

> On Friday 10 January 2003 05:12, Mikael Djurfeldt wrote:
>> Clinton Ebadi <clinton@unknownlamer.org> writes:
>> > I think %modify-instance and -class should be public.
>>
>> Could you be more specific why?  These seem pretty strange and magical
>> to me, and might change as the implementation evolves...
>
> They swap the class in place. It seems that if I don't do that then
> all of my objects that point to the class being changed remain being
> part of that class and then only new objects can be created with the
> changed class. My understanding of the MOP is a bit fuzzy so I'm
> probably wrong.

class-redefinition sets things up so that any future reference to an
object of the old-class will cause it to switch to the new class.
This means that from the moment (class-redfinition old new) is called,
all objects of class old will appear as being of class new.  The
actual update takes place "just-in-time".

>> > I specialized change-class and change-object-class (to the same
>> > thing, just to be safe because the manual says either one may be
>> > called but not both).
>>
>> The manual shouldn't mention change-object-class since that is a
>> private part of the implementation.

Yes.  I've changed that now.

>> Could you please give me enough information to reproduce the infinite
>> loop you are talking about?
>
> My code is at http://unknownlamer.org/files/temp/serialize.scm (it
> has other problems and after I get the class redefinition to work it
> still won't work but I'd just have to do one more thing). I modified
> it and now it says slot 'object is unbound (I marked the line this
> happens at in the source). I didn't want anyone to see it because
> the code is a bit of a hack and sucks...(sorry for taking so long to
> reply but I've had to put in really long shifts at work the last few
> days)

I don't understand why you need to use the class redefinition protocol
in this case.

BTW, (oop goops save) seems to do something related to what you want
to do.

Since I don't understand your code, I can't deduce the intended
correct operation, so I can't understand what is not working correctly
either.  However, I did notice one bug: Your change-class method
doesn't call (next-method).  That is necessary.

Here's a further example of the protocol in operation.  That may give
some  hints:

guile> (use-modules (oop goops))
guile> (define-class c () (x #:init-keyword #:x))
guile> (define o (make c #:x 3))
guile> (define-method (change-class (o c) (new <class>))
                        (next-method)
                        (format #t "~A: ~A\n" o (slot-ref o 'x)))
guile> (define-class c () (x #:init-keyword #:x) (y))
guile> o
#<c 4076bcc0>: 3
#<c 4076bcc0>
guile> 


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