I vaguely remeber that in the context of the withForeignPtr discussion we where once trying to achieve some similar effect (but couldn't come up with something that would work). Do you remember?

Uh, my memory's a bit vague too :-) For a long time we were trying to get cheap allocation/freeing for temporary storage, i.e. a cheap alloca. We managed to achieve that when I realised I could pull a trick with GHC's garbage collector and have "pinned" objects as long as they don't contain any pointers into the heap. So instead of using malloc()/free() for alloca, we allocate a pinned ByteArray# and let the GC free it. (it needs to be pinned so that it can be passed to foreign functions which might re-enter the RTS and trigger GC, etc.) This proposed extension to ForeignPtr is just taking the idea one step further: we can use the same trick for ForeignPtrs too, at least in the common case where you want the finalizer to free() the object again.

Does this, then, effectively solve this old problem? Wouldn't you want newXXX and withXXX variants of the above, too?

The two functions I mentioned are all that's needed: mallocForeignPtr :: Storable a => IO (ForeignPtr a) mallocForeignPtrBytes :: Int -> IO (ForeignPtr a) they both do the job of a combined malloc/newForeignPtr. withForeignPtr still works fine with a ForeignPtr constructed this way. Cheers, Simon