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Macro WITH-ACCESSORS

Syntax

  • with-accessors (slot-entry*) instance-form declaration* form*result*

slot-entry ::= (variable-name accessor-name)

Arguments and Values

Description

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.

Examples

(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))

#<STANDARD-METHOD (SETF THING-X) :BEFORE (T THING) 28226194>

(defparameter *thing1* (make-instance 'thing :x 1 :y 2))

#<THING 43135676>

(defparameter *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*)) (setf 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))

Affected By

Exceptional Situations

The consequences are undefined if any accessor-name is not the name of an accessor for the instance.

See Also

Notes

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))

\issue{DECLS-AND-DOC}