Re: [clisp-list] CLOS: class-wide slots defined at compile-time?

[Sam S. <sd...@gn...>]

> * In message <9F8...@G8...>
> * On the subject of "[clisp-list] CLOS: class-wide slots defined at compile-time?"
> * Sent on Thu, 20 Feb 2003 17:52:21 +0100
> * Honorable "Hoehle, Joerg-Cyril" <Joe...@t-...> writes:
>
> Sam wrote:
> >An alternative would be to add a class prototype (which would waste an
> >instance for each class...)
> 
> The class-prototype hack(?) may be something
> 2) which seems to be somewhat standard in CLOS (I guess from your
> wording), whereas SHARED-SLOT would be specific to CLISP.

it's in MOP.

> Maybe a separate weak hash-table trick may allow to implement a
> singleton class-prototype for all classes for which one was requested
> without spending an extra slot on each class?

> (defvar clos:*class-prototypes* (make-hash-table :Test #'eq :weak :keys))
> ; weak so as not to grow unnecessarily
> (defun class-prototype (class)
>   (check-type class 'standard-class)
>   (or (gethash class *class-prototypes* nil)
>       (setf (gethash class *class-prototypes)
>             (make-weird-instance-full-of #<unbound> slots except for the shared ones or whatever-is-needed))))
> Or maybe that class-prototype should not be an instance of its class
> (but of some other one). Would that be against programmer's
> expectations??

it's better to keep the prototype inside the CLASS struct.
class may be redefined &c.
we may create the prototype on demand.

-- 
Sam Steingold (http://www.podval.org/~sds) running RedHat8 GNU/Linux
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