Goops Manual (original) (raw)
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3.4 Accessing Slots
The definition of a slot contains at the very least a slot name, and may also contain various slot options, including getter, setter and/or accessor functions for the slot.
It is always possible to access slots by name, using the various "slot-ref" and "slot-set!" procedures described in the following subsections. For example,
(define-class () ;; Define a class with slots (count #:init-value 0) ;; named "count" and "cache". (cache #:init-value '()) ...)
(define inst (make )) ;; Make an instance of this class.
(slot-set! inst 'count 5) ;; Set the value of the "count" ;; slot to 5.
(slot-set! inst 'cache ;; Modify the value of the (cons (cons "^it" "It") ;; "cache" slot. (slot-ref inst 'cache)))
If a slot definition includes a getter, setter or accessor function, these can be used instead of slot-ref and slot-set! to access the slot.
(define-class () ;; Define a new class whose slots (count #:setter set-count) ;; use a getter, a setter and (cache #:accessor cache) ;; an accessor. (csize #:getter cache-size) ...)
(define inst (make )) ;; Make an instance of this class.
(set-count inst 5) ;; Set the value of the "count" ;; slot to 5.
(set! (cache inst) ;; Modify the value of the (cons (cons "^it" "It") ;; "cache" slot. (cache inst)))
(let ((size (cache-size inst))) ;; Get the value of the "csize" ...) ;; slot.
Whichever of these methods is used to access slots, GOOPS always calls the low-level getter and setter closures for the slot to get and set its value. These closures make sure that the slot behaves according to the #:allocation type that was specified in the slot definition (see allocation). (For more about these closures, see compute-get-n-set.)