Re: GOOPS: Customizing class instantiation

["Pat Lasswell" <imofftoseethewizard@gmail.com>]

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On 9/26/06, Ludovic Courtès <ludovic.courtes@laas.fr> wrote:

  (define-method (make-instance (c <my-class>))
    (format (current-error-port) "make-instance (~a)~%" c)
    (next-method))

Try adding a '. initargs' after '(c <my-class>)'.

cheers
pat

On 9/26/06, Ludovic Courtès <ludovic.courtes@laas.fr> wrote:
>
> Hi,
>
> I'm trying to "dynamically" create classes which I would then like to
> instantiate.  The behavior I would like to achieve is that:
>
>   guile> (define c (make-a-class 'some-name))
>   guile> (define obj (make c))
>   guile> obj
>   #<<my-class> some-name deadbeef>
>
> To that purpose, I have a metaclass named `<my-class>' and a procedure
> `make-a-class' that simply returns instances of `<my-class>'.  Since
> `compute-cpl' is customized for instances of `<my-class>', I can make
> sure that instances of `<my-class>' have a proper CPL that includes
> `<top>'.  Here's the code:
>
>   (use-modules (oop goops))
>   (read-set! keywords 'prefix)
>
>   (define-class <my-class> (<class>)
>     (the-slot :init-value #t))
>
>
>   (define-method (compute-cpl (c <my-class>))
>     (format (current-error-port) "CPL (~a)~%" c)
>     (list c <top>))
>
>   (define-method (make-instance (c <my-class>))
>     (format (current-error-port) "make-instance (~a)~%" c)
>     (next-method))
>
>
>   (define (make-a-class name)
>     (let ((c (make <my-class>)))
>       (slot-set! c 'name name)
>       c))
>
> The issue is that when instantiating an instance of `<my-class>' (read
> that twice ;-)), I'm getting the following error:
>
>   ;; Create a class (instance of `<my-class>').
>   guile> (define c (make-a-class 'paf))
>   CPL (#<<my-class> ??? 301f8930>)
>   guile> c
>   #<<my-class> paf 301f8930>
>
>   ;; Instantiate it.
>   guile> (make c)
>   make-instance (#<<my-class> paf 301f8930>)
>
>   <unnamed port>: In expression (let* (#) (format # "make-instance (~a)~%"
> ...) ...):
>   <unnamed port>: No applicable method for #<<generic> initialize (10)> in
> call (initialize #<struct 301f8930:301f7320> ())
>   ABORT: (goops-error)
>
> This is quite unexpected since I would expect, at least, the
> `initialize' class for instances of `<top>' to be applicable.  The other
> surprising thing is that the instance to be initialized is still seen as
> #<struct ...> instead of #<paf ...> or some such.
>
> Any idea?
>
> Thanks,
> Ludovic.
>
>
> _______________________________________________
> Guile-user mailing list
> Guile-user@gnu.org
> http://lists.gnu.org/mailman/listinfo/guile-user
>

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