Add unsafeToArray function for getting the underlying boxed Array. Fixes #245

Author: lehins

vector/changelog.md

@@ -47,6 +47,7 @@
 * Add `groupBy` and `group` for `Data.Vector.Generic` and the specialized
   version in `Data.Vector`, `Data.Vector.Unboxed`, `Data.Vector.Storable` and
   `Data.Vector.Primitive`.
+* Add `unsafeToArray` function for getting the underlying boxed `Array`.
 
 # Changes in version 0.12.3.1
 

vector/src/Data/Vector.hs

@@ -163,7 +163,7 @@ module Data.Vector (
   toList, Data.Vector.fromList, Data.Vector.fromListN,
 
   -- ** Arrays
-  fromArray, toArray,
+  fromArray, toArray, unsafeToArray,
 
   -- ** Other vector types
   G.convert,
@@ -2147,6 +2147,17 @@ toArray (Vector offset size arr)
   | offset == 0 && size == sizeofArray arr = arr
   | otherwise = cloneArray arr offset size
 
+-- | /O(1)/ Extract the underlying `Array`, offset where vector starts and the
+-- total number of elements in the vector. Below property always holds:
+--
+-- > let (array, offset, size) = unsafeToArray v
+-- > v === unsafeTake size (unsafeDrop offset (`fromArray` array))
+--
+-- @since 0.13.0.0
+unsafeToArray :: Vector a -> (Array a, Int, Int)
+{-# INLINE unsafeToArray #-}
+unsafeToArray (Vector offset size arr) = (arr, offset, size)
+
 -- Conversions - Mutable vectors
 -- -----------------------------
 

vector/tests/Tests/Vector/UnitTests.hs

@@ -91,6 +91,7 @@ tests =
   , testGroup "Data.Vector"
     [ testCase "MonadFix" checkMonadFix
     , testCase "toFromArray" toFromArray
+    , testCase "toFromArrayUnsafe" toFromArrayUnsafe
     , testCase "toFromMutableArray" toFromMutableArray
     ]
   ]
@@ -202,6 +203,14 @@ toFromArray =
   mkArrayRoundtrip $ \name v ->
     assertEqual name v $ Boxed.fromArray (Boxed.toArray v)
 
+toFromArrayUnsafe :: Assertion
+toFromArrayUnsafe =
+  mkArrayRoundtrip $ \name v ->
+    case Boxed.unsafeToArray v of
+      (arr, off, n) ->
+        assertEqual name v $
+        Boxed.unsafeTake n (Boxed.unsafeDrop off (Boxed.fromArray arr))
+
 toFromMutableArray :: Assertion
 toFromMutableArray = mkArrayRoundtrip assetRoundtrip
   where