with-accessors (slot-entry*) instance-form declaration* form*
slot-entry::= (variable-name accessor-name)
Arguments and Values:
variable-name---a variable name; not evaluated.
accessor-name---a function name; not evaluated.
instance-form---a form; evaluated.
declaration---a declare expression; not evaluated.
forms---an implicit progn.
results---the values returned by the forms.
Creates a lexical environment in which the slots specified by slot-entry are lexically available through their accessors as if they were variables. The macro with-accessors invokes the appropriate accessors to access the slots specified by slot-entry. Both setf and setq can be used to set the value of the slot.
(defclass thing () ((x :initarg :x :accessor thing-x) (y :initarg :y :accessor thing-y))) => #<STANDARD-CLASS THING 250020173> (defmethod (setf thing-x) :before (new-x (thing thing)) (format t "~&Changing X from ~D to ~D in ~S.~%" (thing-x thing) new-x thing)) (setq thing1 (make-instance 'thing :x 1 :y 2)) => #<THING 43135676> (setq thing2 (make-instance 'thing :x 7 :y 8)) => #<THING 43147374> (with-accessors ((x1 thing-x) (y1 thing-y)) thing1 (with-accessors ((x2 thing-x) (y2 thing-y)) thing2 (list (list x1 (thing-x thing1) y1 (thing-y thing1) x2 (thing-x thing2) y2 (thing-y thing2)) (setq x1 (+ y1 x2)) (list x1 (thing-x thing1) y1 (thing-y thing1) x2 (thing-x thing2) y2 (thing-y thing2)) (setf (thing-x thing2) (list x1)) (list x1 (thing-x thing1) y1 (thing-y thing1) x2 (thing-x thing2) y2 (thing-y thing2))))) >> Changing X from 1 to 9 in #<THING 43135676>. >> Changing X from 7 to (9) in #<THING 43147374>. => ((1 1 2 2 7 7 8 8) 9 (9 9 2 2 7 7 8 8) (9) (9 9 2 2 (9) (9) 8 8))
The consequences are undefined if any accessor-name is not the name of an accessor for the instance.
A with-accessors expression of the form:
(with-accessors (slot-entry1 ... slot-entryn) instance-form form1 ... formk)
expands into the equivalent of
(let ((in instance-form)) (symbol-macrolet (Q1 ... Qn) form1 ... formk))
where Qi is
(variable-namei () (accessor-namei in))