@classmethod
def _constructor(cls, alpha, **kwargs):
    """
        Constructs distribution and moments objects.
        """
    retval = super()._constructor(alpha, **kwargs)
    if retval[2] != cls._moments.dims:
        raise ValueError(
            'Parent has wrong dimensionality. Must be a two-dimensional vector.'
            )
    return retval[0], retval[1], retval[2], retval[3
        ], cls._distribution, cls._moments, retval[6]
