with-slots (slot-entry*) instance-form declaration* form*
slot-entry::= slot-name | (variable-name slot-name)
Arguments and Values:
slot-name---a slot name; not evaluated.
variable-name---a variable name; not evaluated.
instance-form---a form; evaluted to produce instance.
declaration---a declare expression; not evaluated.
forms---an implicit progn.
results---the values returned by the forms.
The macro with-slots establishes a lexical environment for referring to the slots in the instance named by the given slot-names as though they were variables. Within such a context the value of the slot can be specified by using its slot name, as if it were a lexically bound variable. Both setf and setq can be used to set the value of the slot.
The macro with-slots translates an appearance of the slot name as a variable into a call to slot-value.
(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 thing (make-instance 'thing :x 0 :y 1)) => #<THING 62310540> (with-slots (x y) thing (incf x) (incf y)) => 2 (values (thing-x thing) (thing-y thing)) => 1, 2 (setq thing1 (make-instance 'thing :x 1 :y 2)) => #<THING 43135676> (setq thing2 (make-instance 'thing :x 7 :y 8)) => #<THING 43147374> (with-slots ((x1 x) (y1 y)) thing1 (with-slots ((x2 x) (y2 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 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 slot-name is not the name of a slot in the instance.
with-accessors, slot-value, symbol-macrolet
A with-slots expression of the form:
(with-slots (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
(slot-entryi () (slot-value in 'slot-entryi))
if slot-entryi is a symbol and is
(variable-namei () (slot-value in 'slot-namei))
if slot-entryi is of the form