Re: `StablePtr` in `ST`
Jon Purdy <[email protected]>
| Newsgroups | gmane.comp.lang.haskell.glasgow.user,gmane.comp.lang.haskell.ghc.devel |
|---|---|
| Message-ID | <CAE3FWBt3XC1yo+3EM7s5LmqaxGH1k+Vmv5JD=uNaVg9RnE5VdA@mail.gmail.com> |
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 <[email protected]> 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 want > this anyway? > > On Wed, Aug 21, 2019, 7:39 AM David Feuer <[email protected]> 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 silly, >> but I guess you pretty much have to assume that anyway. >> >> On Wed, Aug 21, 2019, 5:00 AM Matthew Farkas-Dyck <[email protected]> >> wrote: >> >>> I have been doing some work where i want `StablePtr`, but also to not >>> be confined to `IO`. I saw the following comment in >>> "compiler/prelude/PrimOp.hs": >>> >>> Question: Why @RealWorld@ - won't any instance of @_ST@ do the job? >>> [ADR] >>> >>> 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 >>> [email protected] >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users >>> >> _______________________________________________ > Glasgow-haskell-users mailing list > [email protected] > http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users > _______________________________________________ Glasgow-haskell-users mailing list [email protected] http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users