[Sbcl-devel] customizing compute-slots

[Bruno H. <br...@cl...>]

The MOP spec says about COMPUTE-SLOTS's primary methods: "This method can
be overridden." But when trying to do this, to add a new local or shared slot,
I get an error:

(use-package "SB-PCL")
(defclass b (a) ())
(defmethod compute-slots ((class (eql (find-class 'b))))
  (append (call-next-method)
          (list (make-instance 'standard-effective-slot-definition
                  :name 'y
                  :allocation :instance))))
(defclass a () ((x :allocation :class)))
;; A should now have a shared slot, X, and a local slot, Y.
(mapcar #'slot-definition-location (class-slots (find-class 'b)))
=>
  There is no applicable method for the generic function
    #<STANDARD-GENERIC-FUNCTION CLASS-SLOTS (3)>
  when called with arguments
    (NIL).

(use-package "SB-PCL")
(defclass b (a) ())
(defmethod compute-slots ((class (eql (find-class 'b))))
  (append (call-next-method)
          (list (make-instance 'standard-effective-slot-definition
                  :name 'y
                  :allocation :class))))
(defclass a () ((x :allocation :class)))
;; A should now have two shared slots, X and Y.
(mapcar #'slot-definition-location (class-slots (find-class 'b)))
=>
  There is no applicable method for the generic function
    #<STANDARD-GENERIC-FUNCTION SB-PCL::CLASS-SLOT-CELLS (1)>
  when called with arguments
    (NIL).

Bruno