Re: Copying a CLOS Instance

[Bill St. Clair <bill>]

   Date: 	24 Jun 91 11:21:06 U
   From: "Shetti Dattatraya" <Shetti_Dattatraya@ssdc.honeywell.com>
   Subject: 	Copying a CLOS Instance
   Return-Receipt-To: Shetti_Dattatraya@ssdc.honeywell.com
   Priority: Normal
   To: info-macl@cambridge.apple.com
   
   Given an instance is there a CLOS method to copy it?
   In the XEROX release of PCL we had following cludge..
   
   (defmethod COPY-INSTANCE ((obj T))
     (let ((new (pcl::make-instance (class-name (class-of obj))))
           (islots (pcl::wrapper-instance-slots-layout
                 (pcl::class-wrapper (class-of obj)))))
       (dolist (slot islots)
         (when (slot-boundp obj slot)
           (setf (slot-value new slot)
                 (slot-value obj slot))))
       new))
   
   With the native implementation of CLOS (without metaclass fascility)in
   the Allegro2.0b1 Common Lisp, such a hack will not work.
   
   -Dattatraya Shetti
   Mail address: shetti@ssdc.honeywell.com
   
The following will work for instances which are not generic functions.
It will be included as part of the final release of MCL 2.0

---------------------------------------------------------------------------

(in-package :ccl)
(export 'copy-instance)

(defmethod copy-instance ((instance standard-object))
   (copy-uvector (%maybe-forwarded-instance instance)))