Tim Bradshaw pointed out that my message was not very clear because the test I gave does not demonstrate that an initform's result is used to initialize the slot early, only at which time a slot is initialized. This on the other hand gets closer to the point: (defclass test () ((slot :allocation :class :initform t :initarg :slot))) (defmethod initialize-instance :before ((test test) &key) (format t "Slot value: ~A~%" (slot-value test 'slot))) Fresh SBCL: CL-USER> (make-instance 'test) Slot value: T #<TEST {B8115E1}> Fresh SBCL again: CL-USER> (make-instance 'test :slot nil) Slot value: T #<TEST {B92AC89}> So it appears that even when an initarg is provided, the slot is still initialized to the iniform value prior to anything else. -- Resistance is futile. You will be jazzimilated. Scientific site: http://www.lrde.epita.fr/~didier Music (Jazz) site: http://www.didierverna.com