? (DEFCLASS FOO () ((X :accessor foo-x :INITFORM 123))) #<STANDARD-CLASS FOO> ? (setf foo (make-instance 'foo)) #<FOO #x302001F7ABFD> ? (foo-x foo) 123 ? (setf (foo-x foo) nil) NIL ? (foo-x foo) NIL ? (shared-initialize foo t) ; I would have expected this to set X back to 123 #<FOO #x302001F2BAAD> ? (foo-x foo) NIL