[Haskell-cafe] Nice addition to Foreign: castAny

[Maurí­cio CA]

This could be beside castPtr, castCharToCChar etc.

----

castAny :: (Storable a, Storable b) => a -> b
castAny = unsafePerformIO . genericCast
   where
     genericCast :: (Storable a, Storable b) => a -> IO b
     genericCast v = return undefined >>= \r ->
       allocaBytes (max (sizeOf v) (sizeOf r)) $ \p ->
         poke p v >> if False then return r else peek (castPtr p)

----

GHCi:

    > let a = -1000 :: Int16
    > castAny a :: Word16  -->
    64536
    > castAny a :: Ptr ()
    0xb4c2fc18
    > castAny (castAny a :: Ptr ()) :: Int16
    -1000

    > let b = pi :: CLDouble
    > b
    3.141592653589793
    > castAny b :: CInt
    1413754136
    > castAny b :: Ptr ()
    0x54442d18
    > castAny b :: CFloat
    3.3702806e12
    > castAny b :: Int8
    24


At minimum, this is safer than 'unsafeCoerce'. What do you think?

Best,
Maurício