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patch to 12/7/88
- To: CommonLoops.pa@Xerox.COM
- Subject: patch to 12/7/88
- From: Gregor.pa@Xerox.COM
- Date: Mon, 27 Feb 89 15:26 PST
- Fcc: BD:>Gregor>mail>outgoing-mail-5.text.newest
- Line-fold: no
There is a nasty little bug in optimized slot access in 12/7/88 PCL.
This bug probably exists in AAAI PCL as well, I don't have a set of
sources to check.
This bug manifests itself when:
- a method has more than one specialized argument
- and slot-value is used on a slot of more than one
of the specialized arguments
- and either one of the accessed slots is unbound
or one of the slots is a :class slot
or one of the slots doesn't exist
In this case, you can get an error message from slot-value-using-class
with a totally random slot name. Here is an example of a method that
could have the bug:
(defmethod foo ((p position) (r rectangle))
(with-slots (top left width height) r
(with-slots (x y) p
(setq top y
(values top left width height))))
If for example, the X slot of p is unbound, this would signal an error
saying that p didn't have a height slot!
The following patch fixes this problem. Take a running PCL, edit
vector.lisp to have this fix, and compile and load vector. You don't
need to use compile-pcl, it would do extra work.
This will be installed on arisia shortly.
Xerox internal users: I haven't installed this patch anywhere.
(defun pv-access-trap (instance offset isl &optional (new-value nil nvp))
(let* ((i 0)
(dolist (per-class-slots (cdr isl))
(dolist (slot per-class-slots)
(if (= i offset)
(return-from lookup-slot-name slot)
(when (null slot-name)
(error "Internal Error:~@
Unable to determine the name of the slot from the PV-OFFSET~@
and the ISL. This results from inconsistency between the~@
PV-OFFSET this access was told to use and the ISL for the~@
(setf (slot-value-using-class (class-of instance) instance slot-name)
(slot-value-using-class (class-of instance) instance slot-name))))