anchor.diff:  (defun (setf slot-contents) (new-value slots location)
     (setf (svref slots location) new-value))
   
  +(defun fast-sv-position (value simple-vector)
  +  (dotimes (i (array-dimension simple-vector 0))
  +    (when (eq value (svref simple-vector i))
  +      (return i))))
  +
   (defun std-slot-value (instance slot-name)
  -  (let* ((location (slot-location (class-of instance) slot-name))
  -         (slots (std-instance-slots instance))
  -         (val (slot-contents slots location)))
  -    (if (eq secret-unbound-value val)
  -        (error "The slot ~S is unbound in the object ~S."
  -               slot-name instance)
  -        val)))
  +  (flet ((cached-location ()
  +           (let ((cache (slot-contents (std-instance-slots (class-of instance))
  +                                       *standard-class-slot-cache-position*)))
  +             (when (simple-vector-p cache)
  +               (fast-sv-position slot-name cache)))))
  +    (let* ((location (or (cached-location)
  +                         (slot-location (class-of instance) slot-name)))
  +           (slots (std-instance-slots instance))
  +           (val (slot-contents slots location)))
  +      (if (eq secret-unbound-value val)
  +          (error "The slot ~S is unbound in the object ~S."
  +                 slot-name instance)
  +          val))))
   (defun slot-value (object slot-name)
     (if (eq (class-of (class-of object)) the-class-standard-class)
         (std-slot-value object slot-name)
  
positive.code:     (setf (class-direct-slots class) ())
      (setf (class-direct-default-initargs class) ())
      (setf (class-precedence-list class) (list class))
      (setf (class-slots class) ())
      class))
  ;; (It's now okay to define subclasses of t.)
  
negative.code:        (direct-slots)                     ; :accessor class-direct-slots
         (class-precedence-list)            ; :accessor class-precedence-list
         (effective-slots)                  ; :accessor class-slots
         (slot-position-cache :initform ()) ; :accessor class-slot-cache
         (direct-subclasses :initform ())   ; :accessor class-direct-subclasses
         (direct-methods :initform ())      ; :accessor class-direct-methods
         (direct-default-initargs :initform ())))) ; :accessor class-direct-default-initargs
  