New module: Data.ArrayBuffer.Cast

Author: jamesdbrock

CHANGELOG.md

@@ -8,6 +8,8 @@ Breaking changes:
 
 New features:
 
+- `Data.ArrayBuffer.Cast` (#46 by @jamesdbrock)
+
 Bugfixes:
 
 Other improvements:

src/Data/ArrayBuffer/Cast.purs

@@ -0,0 +1,46 @@
+-- | `DataView` represents unaligned memory of unknown endianness.
+-- |
+-- | `ArrayView` represents arrays of aligned elements of
+-- | local-machine endianness.
+-- | For the cases of `Int8Array`, `Uint8Array`, `Uint8ClampedArray`,
+-- | the elements
+-- | are single bytes, so they are always aligned and they have no
+-- | endianness. Therefore in those cases we can freely cast back and forth
+-- | to `DataView`.
+module Data.ArrayBuffer.Cast
+  ( fromInt8Array
+  , fromUint8Array
+  , fromUint8ClampedArray
+  , toInt8Array
+  , toUint8Array
+  , toUint8ClampedArray
+  ) where
+
+import Data.ArrayBuffer.DataView as DV
+import Data.ArrayBuffer.Typed as AT
+import Data.ArrayBuffer.Types (DataView, Uint8Array, Uint8ClampedArray, Int8Array)
+import Effect (Effect)
+
+-- | Cast an `Int8Array` to a `DataView`.
+fromInt8Array :: Int8Array -> Effect DataView
+fromInt8Array x = DV.part (AT.buffer x) (AT.byteOffset x) (AT.byteLength x)
+
+-- | Cast a `DataView` to an `Int8Array`.
+toInt8Array :: DataView -> Effect Int8Array
+toInt8Array x = AT.part (DV.buffer x) (DV.byteOffset x) (DV.byteLength x)
+
+-- | Cast a `UInt8Array` to a `DataView`.
+fromUint8Array :: Uint8Array -> Effect DataView
+fromUint8Array x = DV.part (AT.buffer x) (AT.byteOffset x) (AT.byteLength x)
+
+-- | Cast a `DataView` to a `Uint8Array`.
+toUint8Array :: DataView -> Effect Uint8Array
+toUint8Array x = AT.part (DV.buffer x) (DV.byteOffset x) (DV.byteLength x)
+
+-- | Cast a `UInt8ClampedArray` to a `DataView`.
+fromUint8ClampedArray :: Uint8ClampedArray -> Effect DataView
+fromUint8ClampedArray x = DV.part (AT.buffer x) (AT.byteOffset x) (AT.byteLength x)
+
+-- | Cast a `DataView` to a `Uint8ClampedArray`.
+toUint8ClampedArray :: DataView -> Effect Uint8ClampedArray
+toUint8ClampedArray x = AT.part (DV.buffer x) (DV.byteOffset x) (DV.byteLength x)

src/Data/ArrayBuffer/ValueMapping.purs

@@ -12,7 +12,8 @@ import Data.Float32 (Float32) as F
 import Data.UInt (UInt)
 import Type.Proxy (Proxy)
 
--- | Map of each `ArrayViewType` to the number of bytes of storage it requires.
+-- | Type-level map of each `ArrayViewType` to the number of bytes of storage
+-- | it requires.
 class BytesPerType (a :: ArrayViewType) where
   byteWidth :: (Proxy a) -> Int
 
@@ -43,7 +44,8 @@ instance bytesPerTypeFloat32 :: BytesPerType Float32 where
 instance bytesPerTypeFloat64 :: BytesPerType Float64 where
   byteWidth _ = 8
 
--- | Maps a `TypedArray`’s binary casted value to its computable representation in JavaScript.
+-- | Type-level map of `TypedArray`’s binary casted value to its
+-- | representation in JavaScript.
 class BinaryValue (a :: ArrayViewType) (t :: Type) | a -> t
 
 instance binaryValueUint8Clamped :: BinaryValue Uint8Clamped UInt
@@ -56,6 +58,7 @@ instance binaryValueInt8 :: BinaryValue Int8 Int
 instance binaryValueFloat32 :: BinaryValue Float32 F.Float32
 instance binaryValueFloat64 :: BinaryValue Float64 Number
 
+-- | Type-level map of `TypedArray` to its element type name.
 class ShowArrayViewType (a :: ArrayViewType) (name :: Symbol) | a -> name
 
 instance showArrayViewTypeUint8Clamped :: ShowArrayViewType Uint8Clamped "Uint8Clamped"