`StablePtr` in `ST`
strake888 at gmail.com
Fri Aug 23 00:19:42 UTC 2019
My colleague responded but said it was rejected from ghc-devs. Message follows:
On 21/08/2019, Jon Purdy <evincarofautumn at gmail.com> wrote:
> Our use case is unsafeCoercing a mutable reference to use as a key in an
> IntMap. Our reasoning is that coercing an IORef/STRef is unsuitable because
> the underlying MutVar# may move, invalidating the key (i.e., you cannot
> safely coerce back if a GC has happened between insertion and reading). (If
> that’s incorrect, do enlighten us!) This is a “very nice to have” for our
> purposes—with the understanding that it’s wicked unsafe. ;)
> On Tue, Aug 20, 2019, 18:09 David Feuer <david.feuer at gmail.com> wrote:
>> You also need to avoid inspecting the StablePtr itself, which is just a
>> number, to maintain purity. The whole thing is a bit weird. Why do you
>> this anyway?
>> On Wed, Aug 21, 2019, 7:39 AM David Feuer <david.feuer at gmail.com> wrote:
>>> So something like
>>> newtype StablePtr a = StablePtr (StablePtrST RealWorld a)?
>>> I suppose that could work with some discipline. You have to assume that
>>> foreign code doesn't pick its address out of a hat and so something
>>> but I guess you pretty much have to assume that anyway.
>>> On Wed, Aug 21, 2019, 5:00 AM Matthew Farkas-Dyck <strake888 at gmail.com>
>>>> I have been doing some work where i want `StablePtr`, but also to not
>>>> be confined to `IO`. I saw the following comment in
>>>> Question: Why @RealWorld@ - won't any instance of @_ST@ do the job?
>>>> It has been there for 20 years. What is the answer? If it is safe i'll
>>>> send the patch generalizing these operations.
>>>> Glasgow-haskell-users mailing list
>>>> Glasgow-haskell-users at haskell.org
>> Glasgow-haskell-users mailing list
>> Glasgow-haskell-users at haskell.org
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