+(defmacro vsc-slot-x-using-class (x x-slot-name computer
+ &key allow-string-fun-p setf-p)
+ (let ((generic-name (intern (concatenate 'string
+ "SLOT-" (string x) "-USING-CLASS"))))
+ `(defmethod ,(if setf-p `(setf ,generic-name) generic-name)
+ (,@(when setf-p '(value))
+ (class virtual-slots-class) (object virtual-slots-object)
+ (slotd effective-virtual-slot-definition))
+ (unless (and (slot-boundp slotd ',x-slot-name)
+ ,@(when allow-string-fun-p
+ `((not (stringp (slot-value slotd ',x-slot-name))))))
+ (setf (slot-value slotd ',x-slot-name) (,computer slotd)))
+ (funcall (slot-value slotd ',x-slot-name)
+ ,@(when setf-p '(value))
+ object))))
+
+(vsc-slot-x-using-class value getter compute-slot-reader-function
+ :allow-string-fun-p t)
+(vsc-slot-x-using-class value setter compute-slot-writer-function
+ :allow-string-fun-p t :setf-p t)
+
+(vsc-slot-x-using-class boundp boundp-function compute-slot-boundp-function)
+(vsc-slot-x-using-class makunbound makunbound-function
+ compute-slot-makunbound-function)
+
+;; In CLISP and SBCL (0.9.15 or newler) a class may not have been
+;; finalized when update-slots are called. So to avoid the possibility
+;; of finalize-instance being called recursivly we have to delay the
+;; initialization of slot functions until after an instance has been
+;; created.
+;; 2007-11-08: done this for all implementations
+;; #?(or (sbcl>= 0 9 15) (featurep :clisp))
+(defmethod slot-unbound (class (slotd effective-virtual-slot-definition) (name (eql 'reader-function)))
+ (declare (ignore class))
+ (setf (slot-value slotd name) (compute-slot-reader-function slotd)))
+
+;; #?(or (sbcl>= 0 9 15) (featurep :clisp))
+(defmethod slot-unbound (class (slotd effective-virtual-slot-definition) (name (eql 'boundp-function)))
+ (declare (ignore class))
+ (setf (slot-value slotd name) (compute-slot-boundp-function slotd)))
+
+;; #?(or (sbcl>= 0 9 15) (featurep :clisp))
+(defmethod slot-unbound (class (slotd effective-virtual-slot-definition) (name (eql 'writer-function)))
+ (declare (ignore class))
+ (setf (slot-value slotd name) (compute-slot-writer-function slotd)))
+
+;; #?(or (sbcl>= 0 9 15) (featurep :clisp))
+(defmethod slot-unbound (class (slotd effective-virtual-slot-definition) (name (eql 'makunbound-function)))
+ (declare (ignore class))
+ (setf (slot-value slotd name) (compute-slot-makunbound-function slotd)))