- Syntax:
-
with-accessors({slot-entry}*)
instance-form{declaration}* {form}*
{result}*
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.
- 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))
(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))
- Affected By:
-
defclass
- Exceptional Situations:
-
The consequences are undefined if any accessor-name is not the name
of an accessor for the instance.
- See Also:
-
with-slots,
symbol-macrolet
- 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))
- Allegro CL Implementation Details:
-
None.