nalaginrut <[email protected]> writes:
> Sorry I think the "update score" is a fake problem. It can be solved by
> #:allocation #:virtual.
> But I still want to talk this topic: "How to hide the critical
> property?"
With apologies for the late reply...
I guess something like this (untested):
(define valid-score-update #f)
(define slot-setter-if-valid-scope #f)
(let ((valid-scope #f))
(set! valid-score-update
(lambda (player newscore)
(set! valid-scope #t)
(slot-set! player 'score newscore)
(set! valid-scope #f)))
(set! slot-setter-if-valid-scope
(lambda (obj new-val)
(or valid-scope
(error "Not in valid scope!"))
(set! (score obj) new-val))))
Then use `valid-score-update' in the definition of the score-update
method, and `slot-setter-if-valid-scope' as the #:slot-set! option of
your virtual 'score slot.
I've assumed that (score obj) provides the real underlying storage for
the virtual slot; it could be a (make-object-property), for example.
Unfortunately I'd say this adds up to an over-contrived solution; but
hopefully it's still useful to show how it _could_ be done.
Regards,
Neil
