LispForum

Untested: (defclass a () ((foo :accessor foo))) (defclass b () ((bar :accessor bar))) (let ((a1 (make-instance 'a)) (b1 (make-instance 'b)) (b2 (make-instance 'b))) (defmethod (setf foo) :after (value (object (eql a1))) (setf (bar b1) (setf (bar b2) value)))) You don't need a special mechanism for t...