- Syntax:
-
with-slots
({slot-entry}*)
instance-form
{declaration}* {form}*
{result}*
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.
instance - an object.
declaration - a declare expression; not evaluated.
forms - an implicit progn.
results - the values returned by the forms.
- Description:
-
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.
- 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 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))
- Affected By:
-
defclass
- Exceptional Situations:
-
The consequences are undefined if any slot-name is not the name
of a slot in the instance.
- See Also:
-
with-accessors,
slot-value,
symbol-macrolet
- Notes:
-
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
(variable-namei
slot-namei)
- Allegro CL Implementation Details:
-
None.
7 Objects