import decorator

class IdDecorator(decorator.Decorator):
    """A decorator that adds a field giving the object behind
    the wrapper."""
    
    __slots__ = ["object"]

    def __init__(self, wrapper, info):
        super(IdDecorator, self).__init__(wrapper, info)
        
        try:
            # Try to get the direct object reference
            self.object = info.object
        except AttributeError:
            # There's not too much overhead if it's not
            # available.
            self.fail(IdDecorator)

    @classmethod
    def picklable(cls):
        return False
    
    @classmethod
    def idempotent(cls, items):
        return super(IdDecorator, cls).idempotent(items) and \
               hasattr(self, "object") == ("object" in items)