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\ignore{
\begin{code}
module DBus.Types.Containers.Variant
( Variant (..)
, Variable (..)
, variantSignature
, variantType
) where
import Data.Typeable (Typeable, cast)
import Data.Word (Word8, Word16, Word32, Word64)
import Data.Int (Int16, Int32, Int64)
import qualified DBus.Types.Signature as S
import qualified DBus.Types.ObjectPath as O
\end{code}
}
\subsubsection{Variants}
Any value which can be converted to a {\tt Variant} can be stored in D-Bus
containers or marshaled. Additionally, external types may implement the
{\tt Variable} interface to provide custom conversion to/from built-in D-Bus
types.
The {\tt defaultSignature} function will be passed {\tt unknown} to determine
the signature an empty array or dictionary.
\begin{code}
class Variable a where
defaultSignature :: a -> S.Signature
toVariant :: a -> Variant
fromVariant :: Variant -> Maybe a
\end{code}
\begin{code}
data Variant = forall a. (Variable a, Typeable a, Show a) =>
Variant S.Signature a
deriving (Typeable)
instance Show Variant where
showsPrec d (Variant sig x) = showParen (d > 10) $
s "Variant " . s sigStr . s " " . showsPrec 11 x
where sigStr = show . S.strSignature $ sig
s = showString
\end{code}
Ghetto Eq instance -- the types contained in variants are known to have
fixed {\tt show} representations, so this works well enough.
It might not work right for {\tt Double}, though.
\begin{code}
instance Eq Variant where
x == y = show x == show y
\end{code}
Variants are themselves variables.
\begin{code}
instance Variable Variant where
defaultSignature _ = S.mkSignature' "v"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
variantSignature :: Variant -> S.Signature
variantSignature (Variant s _) = s
\end{code}
\begin{code}
variantType :: Variant -> S.Type
variantType = head . S.signatureTypes . variantSignature
\end{code}
\begin{code}
instance Variable Bool where
defaultSignature _ = S.mkSignature' "b"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable Word8 where
defaultSignature _ = S.mkSignature' "y"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable Word16 where
defaultSignature _ = S.mkSignature' "q"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable Word32 where
defaultSignature _ = S.mkSignature' "u"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable Word64 where
defaultSignature _ = S.mkSignature' "t"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable Int16 where
defaultSignature _ = S.mkSignature' "n"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable Int32 where
defaultSignature _ = S.mkSignature' "i"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable Int64 where
defaultSignature _ = S.mkSignature' "x"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable Double where
defaultSignature _ = S.mkSignature' "d"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable String where
defaultSignature _ = S.mkSignature' "s"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable O.ObjectPath where
defaultSignature _ = S.mkSignature' "o"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\begin{code}
instance Variable S.Signature where
defaultSignature _ = S.mkSignature' "g"
toVariant = toVariant'
fromVariant = fromVariant'
\end{code}
\subsubsection*{Helper functions}
\begin{code}
toVariant' :: (Variable a, Typeable a, Show a) => a -> Variant
toVariant' x = Variant (defaultSignature x) x
fromVariant' :: Typeable a => Variant -> Maybe a
fromVariant' (Variant _ x) = cast x
\end{code}