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Re: modifying pointers

From: Andy Wingo
Subject: Re: modifying pointers
Date: Fri, 09 Apr 2010 18:59:16 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux)


On Fri 09 Apr 2010 18:30, address@hidden (Ludovic Courtès) writes:

> Andy Wingo <address@hidden> writes:
>> You added a change to foreign-set! for %null-pointer. Would it not make
>> sense instead to make foreign pointers of type "void" unsettable?
> Not necessarily.  See the test that was added:
>   (pass-if "foreign-set! other-null-pointer"
>     (let ((f (bytevector->foreign (make-bytevector 2))))
>       (and (not (= 0 (foreign-ref f)))
>            (begin
>              (foreign-set! f 0)
>              (= 0 (foreign-ref f)))
>            (begin
>              ;; Here changing the pointer value of F is perfectly valid.
>              (foreign-set! f 777)
>              (= 777 (foreign-ref f))))))
> Here a ((void *) 777) pointer is created.

I'm just wondering if it is valid to create a ((void*) 777) pointer.
Under what condition is that useful?

If that is useful, OK; but under what condition is it useful to mutate
the pointer in a foreign pointer object? Why not create a new foreign
pointer object?


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