Hello, it seems that until now, I've been relying on a non-standard behavior, namely the fact that shared slots with an :initform are initialized before the first actual class instance is created: (defclass test () ((slot :allocation :class :initform t))) (defmethod initialize-instance :before ((test test) &key) (format t "Slot boundp: ~A~%" (slot-boundp test 'slot))) CL-USER> (make-instance 'test) Slot boundp: NIL #<TEST {C5D3B8}> CL-USER> (make-instance 'test) Slot boundp: T #<TEST {14563D4}> CL-USER> I just fell on this because every other Common Lisp implementation I've tried gives T and T here. Is it due to the way CLOS is implemented in ABCL, and is there a chance that this can be improved? Thanks. -- Resistance is futile. You will be jazzimilated. Scientific site: http://www.lrde.epita.fr/~didier Music (Jazz) site: http://www.didierverna.com