LumiGuide
diff --git a/‎opencv/src/OpenCV/Core/Types/Mat/HMat.hs
Lines changed: 1 addition & 0 deletions b/‎opencv/src/OpenCV/Core/Types/Mat/HMat.hs
Lines changed: 1 addition & 0 deletions
diff --git a/‎opencv/src/OpenCV/Internal/Core/Types/Mat.hs
Lines changed: 43 additions & 2 deletions b/‎opencv/src/OpenCV/Internal/Core/Types/Mat.hs
Lines changed: 43 additions & 2 deletions
diff --git a/‎opencv/src/OpenCV/Internal/Core/Types/Mat/HMat.hs
Lines changed: 20 additions & 1 deletion b/‎opencv/src/OpenCV/Internal/Core/Types/Mat/HMat.hs
Lines changed: 20 additions & 1 deletion
@@ -11,6 +11,7 @@ module OpenCV.Core.Types.Mat.HMat
 
     , matToHMat
     , hMatToMat
+    , withHMatAsMat
     ) where
 
 import "this" OpenCV.Internal.Core.Types.Mat.HMat
@@ -31,6 +31,7 @@ module OpenCV.Internal.Core.Types.Mat
     , keepMatAliveDuring
     , newEmptyMat
     , newMat
+    , withMat
     , withMatData
     , matToVec
     , vecToMat
@@ -49,6 +50,7 @@ module OpenCV.Internal.Core.Types.Mat
 
     , mkMatM
     , createMat
+    , unsafeFinalizeMat
     , withMatM
     , cloneMatM
     , deallocateMatM
@@ -83,7 +85,7 @@ module OpenCV.Internal.Core.Types.Mat
     , ValidChannels'
     ) where
 
-import "base" Control.Exception ( throwIO, mask_ )
+import "base" Control.Exception ( throwIO, mask_, bracket )
 import "base" Control.Monad ( when )
 import "base" Control.Monad.IO.Class
 import "base" Control.Monad.ST ( ST )
@@ -94,10 +96,11 @@ import qualified "base" Data.List.NonEmpty as NE
 import "base" Data.Maybe
 import "base" Data.Monoid ( (<>) )
 import "base" Data.Proxy
+import "base" Data.Traversable ( for )
 import "base" Data.Word
 import "base" Foreign.C.Types
 import "base" Foreign.ForeignPtr
-    ( ForeignPtr, withForeignPtr, touchForeignPtr, newForeignPtr, newForeignPtr_ )
+    ( ForeignPtr, withForeignPtr, touchForeignPtr, newForeignPtr, newForeignPtr_, finalizeForeignPtr )
 import "base" Foreign.Marshal.Alloc ( alloca )
 import "base" Foreign.Marshal.Array ( allocaArray, peekArray )
 import "base" Foreign.Marshal.Utils ( toBool )
@@ -400,6 +403,44 @@ newMat shape channels depth defValue = do
     depth'    = toDepth depth
     defValue' = toScalar defValue
 
+-- | Frees the data underlying the Mat.
+--
+-- Only use it if you can guarantee that the Mat isn't used
+-- afterwards!
+unsafeFinalizeMat
+    :: Mat shape channels depth -- ^ The matrix to be finalised.
+    -> IO ()
+unsafeFinalizeMat mat = do
+  finalizeForeignPtr (unMat mat)
+
+-- | Like `newMat`, but provides scoped access to the matrix
+-- and it's guaranteed to be freed when this function returns.
+--
+-- Use this instead of `newMat` where you can (where the matrix
+-- needs only lexically scocped life time).
+--
+-- Thus you must not return the matrix outside of the scope.
+withMat
+    :: ( ToShape    shape
+       , ToChannels channels
+       , ToDepth    depth
+       , ToScalar   scalar
+       , MonadError CvException m
+       , MonadIO m
+       )
+    => shape -- ^
+    -> channels
+    -> depth
+    -> scalar
+    -> (Mat (ShapeT shape) (ChannelsT channels) (DepthT depth) -> IO a)
+    -> m a
+withMat shape channels depth defValue action =
+  wrapException $ liftIO $ do
+    bracket
+      (runExceptT $ newMat shape channels depth defValue)
+      (\eMat -> for eMat $ \mat -> unsafeFinalizeMat mat) -- free Mat promptly
+      (\eMat -> for eMat $ \mat -> action mat)
+
 -- TODO (BvD): Move to some Utility module.
 withVector
     :: (VG.Vector v a, Storable a)
 
@@ -13,8 +13,10 @@ module OpenCV.Internal.Core.Types.Mat.HMat
 
     , matToHMat
     , hMatToMat
+    , withHMatAsMat
     ) where
 
+import "base" Control.Exception ( bracket )
 import "base" Data.Foldable
 import "base" Data.Int
 import "base" Data.Word
@@ -124,7 +126,10 @@ matToHMat mat = unsafePerformIO $ withMatData mat $ \step dataPtr -> do
             VU.unsafeFreeze v
 
 hMatToMat :: HMat -> Mat 'D 'D 'D
-hMatToMat (HMat shape channels elems) = unsafePerformIO $ do
+hMatToMat hMat = unsafePerformIO $ hMatToMatIO hMat
+
+hMatToMatIO :: HMat -> IO (Mat 'D 'D 'D)
+hMatToMatIO (HMat shape channels elems) = do
     mat <- exceptErrorIO $ newMat sizes channels depth scalar
     withMatData mat copyElems
     pure mat
@@ -153,6 +158,20 @@ hMatToMat (HMat shape channels elems) = unsafePerformIO $ do
               for_ [0 .. channels - 1] $ \channelIx ->
                 pokeElemOff elemPtr (fromIntegral channelIx) $ VU.unsafeIndex v (fromIntegral $ posIx + channelIx)
 
+-- | Like `hMatToMat`, but provides scoped access to the matrix
+-- and it's guaranteed to be freed when this function returns.
+--
+-- Use this instead of `hMatToMat` where you can (where the matrix
+-- needs only lexically scocped life time).
+--
+-- Thus you must not return the matrix outside of the scope.
+withHMatAsMat :: HMat -> (Mat 'D 'D 'D -> IO a) -> IO a
+withHMatAsMat hMat action = do
+  bracket
+    (hMatToMatIO hMat)
+    (\mat -> unsafeFinalizeMat mat)
+    action
+
 product0 :: (Num a) => [a] -> a
 product0 [] = 0
 product0 xs = product xs