Merge pull request #769 from IntersectMBO/jdral/serialisekey-void

A `SerialiseKey` instance for `Void`

Author: jorisdral

src/Database/LSMTree/Internal/Serialise/Class.hs

@@ -510,11 +510,13 @@ instance SerialiseValue P.ByteArray where
   Void
 -------------------------------------------------------------------------------}
 
-{- |
-This instance is intended for tables without blobs.
+-- | The implementation of 'deserialiseKey' throws an exception.
+instance SerialiseKey Void where
+  serialiseKey = absurd
+  deserialiseKey = error "deserialiseKey: cannot deserialise into Void"
 
-The implementation of @'deserialiseValue'@ throws an excepValuen.
--}
+
+-- | The implementation of 'deserialiseValue' throws an exception.
 instance SerialiseValue Void where
   serialiseValue = absurd
   deserialiseValue = error "deserialiseValue: cannot deserialise into Void"

src/Database/LSMTree/Internal/Types.hs

@@ -19,6 +19,7 @@ import           Control.DeepSeq (NFData (..), deepseq)
 import           Data.Kind (Type)
 import           Data.Semigroup (Sum)
 import           Data.Typeable
+import           Data.Void (Void)
 import           Data.Word (Word64)
 import qualified Database.LSMTree.Internal.BlobRef as Unsafe
 import           Database.LSMTree.Internal.RawBytes (RawBytes (..))
@@ -225,4 +226,6 @@ instance ResolveValue (ResolveAsFirst v) where
   resolveSerialised :: Proxy (ResolveAsFirst v) -> RawBytes -> RawBytes -> RawBytes
   resolveSerialised _p = const
 
+deriving via ResolveViaSemigroup Void instance ResolveValue Void
+
 deriving via (ResolveViaSemigroup (Sum v)) instance (Num v, SerialiseValue v) => ResolveValue (Sum v)