8.7.3 Inheritance and accessors

When a class <A> defines a getter, setter or accessor for one of its slots x, an accessor method specialized to class <A> is created. Accessor methods are special in that they always refer to a concrete class. When you subclass <A>, a new accessor method for x is created automatically, specialized to the subclass:

(define-class <A> () (x #:accessor x))
(define-class <B> (<A>))
(generic-function-methods x)
⇒
(#<<accessor-method> (<B>) 7faa66b5b1c0>
 #<<accessor-method> (<A>) 7faa66b5b240>)

Note, in particular, that the x accessor method specialized to <A> is not applicable to objects of class B:

(define o (make <B>))
(compute-applicable-methods x (list o))
⇒
(#<<accessor-method> (<B>) 7faa66b5b1c0>)

As a consequence, an accessor doesn’t have a next-method. The fact that accessor methods always apply to concrete classes allows for extensive optimization.