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{-# LANGUAGE DataKinds, FlexibleInstances, MultiParamTypeClasses,
UndecidableInstances, KindSignatures, TypeFamilies, TypeOperators #-}
#if !MIN_VERSION_base(4,8,0)
{-# LANGUAGE OverlappingInstances #-}
#endif
-- | `Constructible` types are those for which `new` is
-- defined. Often these are `GObject`s, but it is possible to
-- construct new (zero-initialized) structures and unions too.
module Data.GI.Base.Constructible
( Constructible(..)
) where
import Control.Monad.IO.Class (MonadIO)
import Data.GI.Base.Attributes (AttrOp, AttrOpTag(..))
import Data.GI.Base.BasicTypes (GObject, ManagedPtr)
import Data.GI.Base.GObject (constructGObject)
-- | Constructible types, i.e. those which can be allocated by `new`.
class Constructible a (tag :: AttrOpTag) where
-- | Allocate a new instance of the given type, with the given attributes.
new :: MonadIO m => (ManagedPtr a -> a) -> [AttrOp a tag] -> m a
-- | Default instance, assuming we have a `GObject`.
instance {-# OVERLAPPABLE #-}
(GObject a, tag ~ 'AttrConstruct) => Constructible a tag where
new = constructGObject
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