diff --git a/Data/TCache/Defs.hs b/Data/TCache/Defs.hs
--- a/Data/TCache/Defs.hs
+++ b/Data/TCache/Defs.hs
@@ -101,9 +101,12 @@
 class Serializable a  where
   serialize   :: a -> B.ByteString
   deserialize :: B.ByteString -> a
+  deserialKey :: String -> B.ByteString -> a
+  deserialKey _ v= deserialize v
   setPersist  :: a -> Maybe Persist              -- ^ `defaultPersist` if Nothing
   setPersist =  const Nothing
 
+type Key= String
 --instance (Show a, Read a)=> Serializable a where
 --  serialize= show
 --  deserialize= read
@@ -112,9 +115,9 @@
 -- | a persist mechanism has to implement these three primitives
 -- 'filePersist' is the default file persistence
 data Persist = Persist{
-       readByKey   ::  (String -> IO(Maybe B.ByteString)) -- ^  read by key. It must be strict
-     , write       ::  (String -> B.ByteString -> IO())   -- ^  write. It must be strict
-     , delete      ::  (String -> IO())}                  -- ^  delete
+       readByKey   ::  (Key -> IO(Maybe B.ByteString)) -- ^  read by key. It must be strict
+     , write       ::  (Key -> B.ByteString -> IO())   -- ^  write. It must be strict
+     , delete      ::  (Key -> IO())}                  -- ^  delete
 
 -- | Implements default persistence of objects in files with their keys as filenames
 filePersist   = Persist
@@ -198,7 +201,7 @@
 defReadResourceByKey k= iox where
     iox= do
       let Persist f _ _ = getPersist  x
-      f  file >>=  evaluate . fmap  deserialize
+      f  file >>=  evaluate . fmap  (deserialKey k)
       where
       file= defPath x ++ k
       x= undefined `asTypeOf` (fromJust $ unsafePerformIO iox)
diff --git a/TCache.cabal b/TCache.cabal
--- a/TCache.cabal
+++ b/TCache.cabal
@@ -1,5 +1,5 @@
 name: TCache
-version: 0.10.2.3
+version: 0.10.2.4
 cabal-version: >= 1.6
 build-type: Simple
 license: BSD3