Subject: Re: Inherited shared slots From: Erik Naggum <firstname.lastname@example.org> Date: 1998/04/13 Newsgroups: comp.lang.lisp Message-ID: <email@example.com> * Erann Gat | Here's a puzzle for you CLOS and MOP wizards. I'll try to answer, anyway. | Is there a way to have a slot variable that is inherited as a class | allocated variable in the sub-class? sorry to be so elaborate, but do you mean as in this example: (defclass foo () ((zot :allocation :class))) (defclass bar (foo) ()) that (eq (setf (slot-value (make-instance 'bar) 'zot) (cons nil nil)) (slot-value (make-instance 'bar) 'zot)) should yield T? if so, you're in luck, because this is already the specified behavior of shared slots, _unless_ you create a new slot with the same name. here's what the HyperSpec says on this issue (7.5.3): A consequence of the allocation rule is that a shared slot can be shadowed. For example, if a class C1 defines a slot named S whose value for the :allocation slot option is :class, that slot is accessible in instances of C1 and all of its subclasses. However, if C2 is a subclass of C1 and also defines a slot named S, C1's slot is not shared by instances of C2 and its subclasses. When a class C1 defines a shared slot, any subclass C2 of C1 will share this single slot unless the defclass form for C2 specifies a slot of the same name or there is a superclass of C2 that precedes C1 in the class precedence list of C2 that defines a slot of the same name. hope this helps. #:Erik -- religious cult update in light of new scientific discoveries: "when we cannot go to the comet, the comet must come to us."