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Re: modifying pointers

From: Andy Wingo
Subject: Re: modifying pointers
Date: Fri, 09 Apr 2010 22:15:21 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux)


On Fri 09 Apr 2010 21:46, address@hidden (Ludovic Courtès) writes:

> Andy Wingo <address@hidden> writes:
>> I'm just wondering if it is valid to create a ((void*) 777) pointer.
>> Under what condition is that useful?
> It opens the door to all sorts of crazy things.  :-)

Cool :)

FWIW, let's kick that door off its hinges :-)))

>> 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?
> There’s currently no procedure to create a foreign object from a
> bignum.

Perhaps we should define one then. It would be more expressive. Also it
avoids all kinds of shared-state problems.

> (Besides, ‘foreign-set!’ exists and has always been defined for all
> types of foreign pointer objects.)

Sure, but this might be an accident. In every case except `void',
foreign-set! modifies the pointed-to memory. Perhaps we need a
foreign-pointer accessor instead, which would work on pointers to values
as well. And a constructor of course.


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