Ptr.hs

{-# OPTIONS_HADDOCK hide #-}

-- NOTE: For now, this module is classified "Support" because the definitions
-- are re-exported from the runtime prelude. Should we add definitions intended
-- for qualified import, we need to add a public module.

-- | Pointer utilities
module HsBindgen.Runtime.Support.Ptr (
  plusPtrElem,
  safeCastFunPtr,
) where

import Data.Coerce (Coercible, coerce)
import Foreign.Ptr
import Foreign.Storable

-- | Advances the given address by the given offset in number of elements of
-- type @a@.
--
-- Examples:
--
-- > plusPtr (_ :: Ptr Word32) 2 -- moves the pointer by 2 bytes
-- > plusPtrElem (_ :: Ptr Word32) 2 -- moves the pointer by 2*4=8 bytes
--
-- NOTE: if @a@ is an instance of 'Data.Primitive.Types.Prim', then you can
-- alternatively use 'Data.Primitive.Ptr.advancePtr'.
plusPtrElem :: forall a. (Storable a) => Ptr a -> Int -> Ptr a
plusPtrElem ptr i = ptr `plusPtr` (i * sizeOf (undefined :: a))

-- | Safely casts a 'FunPtr' to a 'FunPtr' of a different type.
safeCastFunPtr
  :: forall a b. (Coercible a b) => FunPtr a -> FunPtr b
safeCastFunPtr = castFunPtr
 where
  _unused :: a -> b
  _unused = coerce