    {-# 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 :: forall (m :: * -> *).
    MonadIO m =>
    (ManagedPtr a -> a) -> [AttrOp a tag] -> m a
    new = (ManagedPtr a -> a) -> [AttrOp a tag] -> m a
    (ManagedPtr a -> a) -> [AttrOp a 'AttrConstruct] -> m a
    forall o (m :: * -> *).
    (GObject o, MonadIO m) =>
    (ManagedPtr o -> o) -> [AttrOp o 'AttrConstruct] -> m o
    constructGObject