Consider the following code:
(defclass whitespace-normalizer (sax-proxy))
(defclass sax-proxy (broadcast-handler) ())
(defclass broadcast-handler () ((handlers :initform nil :initarg :handlers :accessor broadcast-handler-handlers)))
Doing the followoing results in errors:
(setf (broadcast-handler-handlers (make-instance 'whitespace-normalizer)) 10)
There is no applicable method for the generic function #<STANDARD-GENERIC-FUNCTION (SETF BROADCAST-HANDLER-HANDLERS) {6621477C}> when called with arguments (10 #<WHITESPACE-NORMALIZER {14BAAEA8}>).
(setf (broadcast-handler-handlers (make-instance 'sax-proxy)) 10)
The slot HANDLERS is missing from the class #<STANDARD-CLASS SAX-PROXY {1700FFDB}>.
The problem is that whitespace-normalizer and sax-proxy are finalized too early.
Finalization happens in std-after-initialization-for-classes http://trac.common-lisp.net/armedbear/browser/trunk/abcl/src/org/armedbear/l...
by calling maybe-finalize-class-subtree, which in its turn finalizes the class and its subclasses in case the class has all its superclasses finalized.
When (defclass whitespace-normalizer (sax-proxy)) is executed it creates a forward-referenced-class for sax-proxy, and when sax-proxy is defined it calls a method for ensure-class-using-class http://trac.common-lisp.net/armedbear/browser/trunk/abcl/src/org/armedbear/l... for forward-referenced-classes. Before calling reinitialize-instance it does (change-class class metaclass) to change from forward-referenced to normal class. change-class in its turn calls shared-initialize method, which calls the aforementioned std-after-initialization-for-classes, but it doesn't supply any direct-superclass arguments. So, when maybe-finalize-class-subtree is called it thinks that sax-proxy's sole superclass is standard-object, so it goes ahead finalizing sax-proxy and whitespace-normalizer at the wrong time with wrong information. And ensure-class-using-class later call with the right direct-superclass information doesn't matter anymore, since the classes were already badly finalized