Proposed change to ForeignPtr

[Alastair Reid]

Alastair wrote [snip]
> makeForeignPtr :: Ptr a -> FunPtr (Ptr a -> IO ()) -> IO ForeignObj

> [snip] I don't understand this proposal.  What is a ForeignObj?

Sorry, that was a typo.  The result type should be 

  IO (ForeignPtr a)

> I call a C function, which gives me a cString :: Ptr CChar, and it's
> my responsibility to free it when I've finished with it.  So I
> convert it to a ForeignPtr:

>    foreignPtr <- mkForeignPtr cString

> and then always refer to the pointer via foreignPtr.  When
> foreignPtr is garbage collected the space is freed.  So how do I do
> this with your proposal?

With the existing spec, you would write:

> foreign import free :: Ptr CChar -> IO ()
>
> foo = do
>   ...
>   foreignPtr <- newForeignPtr cString (free cString)
>   ...

With my proposal, you would write:

> foreign import "&" free :: FunPtr (Ptr CChar -> IO ())
>
> foo = do
>   ...
>   foreignPtr <- newForeignPtr cString free
>   ...

All the rest of your code to manipulate ForeignPtrs remains the same.
(Well, there's a corresponding change in addForeignFinalizer if you
happen to use that.)


-- 
Alastair Reid                 alastair at reid-consulting-uk.ltd.uk  
Reid Consulting (UK) Limited  http://www.reid-consulting-uk.ltd.uk/alastair/