A desirable Boxed instance for Unboxed - #508

data Foo a = Foo Int a
  deriving (Eq, Ord, Show)

instance NFData a => VU.IsoUnbox (Foo a) (Int, AsBoxedStrictly a) where
  toURepr (Foo i a) = (i, makeBoxedStrictly a)
  fromURepr (i, a) = Foo i $ grabBoxedStrictly a
  {-# INLINE toURepr #-}
  {-# INLINE fromURepr #-}
  
newtype instance VU.MVector s (Foo a) = MV_Foo (VU.MVector s (Int, AsBoxedStrictly a))

newtype instance VU.Vector    (Foo a) = V_Foo  (VU.Vector    (Int, AsBoxedStrictly a))

deriving via (Foo a `VU.As` (Int, AsBoxedStrictly a)) instance NFData a => VGM.MVector VUM.MVector (Foo a)

deriving via (Foo a `VU.As` (Int, AsBoxedStrictly a)) instance NFData a => VG.Vector   VU.Vector   (Foo a)

instance NFData a => VU.Unbox (Foo a)

import qualified Data.Vector.Unboxed as VU
VU.fromListN 3 [ Foo 4 "Hello", Foo 8 "there", Foo 16 "sailor" ]
[Foo 4 "Hello",Foo 8 "there",Foo 16 "sailor"]

data Bar a = Bar Int a
  deriving (Eq, Ord, Show)

instance VU.IsoUnbox (Bar a) (Int, AsBoxedLazily a) where
  toURepr (Bar i a) = (i, AsBoxedLazily a)
  fromURepr (i, AsBoxedLazily a) = Bar i a
  {-# INLINE toURepr #-}
  {-# INLINE fromURepr #-}
  
newtype instance VU.MVector s (Bar a) = MV_Bar (VU.MVector s (Int, AsBoxedLazily a))

newtype instance VU.Vector    (Bar a) = V_Bar  (VU.Vector    (Int, AsBoxedLazily a))

deriving via (Bar a `VU.As` (Int, AsBoxedLazily a)) instance VGM.MVector VUM.MVector (Bar a)

deriving via (Bar a `VU.As` (Int, AsBoxedLazily a)) instance VG.Vector   VU.Vector   (Bar a)

instance VU.Unbox (Bar a)

import qualified Data.Vector.Unboxed as VU
VU.fromListN 3 [ Bar 3 "Bye", Bar 2 "for", Bar 1 "now" ]
[Bar 3 "Bye",Bar 2 "for",Bar 1 "now"]