anchor.diff:                       #'std-compute-class-precedence-list
                        #'compute-class-precedence-list)
                    class))
  -  (setf (class-slots class)
  -        (funcall (if (std-class-p (class-of class))
  -                     #'std-compute-slots
  -                     #'compute-slots)
  -                 class))
  +  (setf (class-slots class) (compute-slots class))
     (let* ((instance-slots (remove-if-not 'instance-slot-p
                                           (class-slots class)))
            (layout (make-array (length instance-slots))))
  
positive.code: (defmethod reinitialize-instance :before ((class built-in-class) &rest args)
    (error "Cannot reinitialize built-in classes."))
  
  (defmethod finalize-inheritance ((class built-in-class))
    (std-finalize-inheritance class)
    (values))
  (defmethod compute-slots ((class built-in-class))
    (std-compute-slots class))
  (defmethod compute-class-precedence-list ((class built-in-class))
    (std-compute-class-precedence-list class))
  
  ;;; Structure-class.
  
  (defclass structure-class (clos-class)
  
negative.code: (defmethod compute-slots ((class std-class))
    (std-compute-slots class))
  
  (defmethod compute-slots :around ((class std-class))
    (let ((effective-slots (call-next-method)))
      (std-compute-slot-layouts class effective-slots)
      effective-slots))
  
  (defgeneric compute-effective-slot-definition (class name direct-slots))
  (defmethod compute-effective-slot-definition ((class std-class) name direct-slots)
    (std-compute-effective-slot-definition class name direct-slots))
  