Use Vector for column table for constant element access

lib/Database/PostgreSQL/Opium.hs

@@ -10,11 +10,13 @@
 {-# LANGUAGE TypeOperators #-}
 
 module Database.PostgreSQL.Opium
-  ( Error (..)
+  ( ColumnTable
+  , Error (..)
   , ErrorPosition (..)
   , FromField (..)
   , FromRow (..)
   , fetch_
+  , toListColumnTable
   )
   where
 
@@ -24,6 +26,7 @@ import Data.ByteString (ByteString)
 import Data.IORef (IORef, modifyIORef', newIORef, readIORef)
 import Data.Proxy (Proxy (..))
 import Data.Text (Text)
+import Data.Vector (Vector)
 import Database.PostgreSQL.LibPQ
   ( Column
   , Connection
@@ -36,6 +39,7 @@ import GHC.TypeLits (KnownSymbol, symbolVal)
 
 import qualified Data.Text as Text
 import qualified Data.Text.Encoding as Encoding
+import qualified Data.Vector as Vector
 import qualified Database.PostgreSQL.LibPQ as LibPQ
 
 import Database.PostgreSQL.Opium.Error (Error (..), ErrorPosition (..))
@@ -57,20 +61,26 @@ execParams conn query = do
 fetch_ :: forall a. FromRow a => Connection -> ByteString -> IO (Either Error [a])
 fetch_ conn query = runExceptT $ do
   result <- execParams conn query
-  -- TODO: Use unboxed array for columnTable
   columnTable <- ExceptT $ getColumnTable @a Proxy result
   nRows <- liftIO $ LibPQ.ntuples result
   mapM (ExceptT . fromRow result columnTable) [0..nRows - 1]
 
-type ColumnTable = [(Column, Oid)]
+newtype ColumnTable = ColumnTable (Vector (Column, Oid))
+  deriving (Eq, Show)
+
+newColumnTable :: [(Column, Oid)] -> ColumnTable
+newColumnTable = ColumnTable . Vector.fromList
 
 indexColumnTable :: ColumnTable -> Int -> (Column, Oid)
-indexColumnTable = (!!)
+indexColumnTable (ColumnTable v) i = v `Vector.unsafeIndex` i
+
+toListColumnTable :: ColumnTable -> [(Column, Oid)]
+toListColumnTable (ColumnTable v) = Vector.toList v
 
 class FromRow a where
   getColumnTable :: Proxy a -> Result -> IO (Either Error ColumnTable)
   default getColumnTable :: (Generic a, GetColumnTable' (Rep a)) => Proxy a -> Result -> IO (Either Error ColumnTable)
-  getColumnTable Proxy = runExceptT . getColumnTable' @(Rep a) Proxy
+  getColumnTable Proxy = runExceptT . fmap newColumnTable . getColumnTable' @(Rep a) Proxy
 
   fromRow :: Result -> ColumnTable -> Row -> IO (Either Error a)
   default fromRow :: (Generic a, FromRow' (Rep a)) => Result -> ColumnTable -> Row -> IO (Either Error a)
@@ -79,7 +89,7 @@ class FromRow a where
     runExceptT $ to <$> fromRow' (FromRowCtx result columnTable iRef) row
 
 class GetColumnTable' f where
-  getColumnTable' :: Proxy (f p) -> Result -> ExceptT Error IO ColumnTable
+  getColumnTable' :: Proxy (f p) -> Result -> ExceptT Error IO [(Column, Oid)]
 
 instance GetColumnTable' f => GetColumnTable' (M1 D c f) where
   getColumnTable' Proxy = getColumnTable' @f Proxy
@@ -91,7 +101,7 @@ instance (GetColumnTable' f, GetColumnTable' g) => GetColumnTable' (f :*: g) whe
   getColumnTable' Proxy result =
     (++) <$> getColumnTable' @f Proxy result <*> getColumnTable' @g Proxy result
 
-checkColumn :: forall a. FromField a => Proxy a -> String -> Result -> ExceptT Error IO ColumnTable
+checkColumn :: forall a. FromField a => Proxy a -> String -> Result -> ExceptT Error IO [(Column, Oid)]
 checkColumn Proxy nameStr result = do
   column <- ExceptT $ maybe (Left $ ErrorMissingColumn nameText) Right <$> LibPQ.fnumber result name
   oid <- liftIO $ LibPQ.ftype result column