def to_regular_array(self, A):
        """
        Converts from an array of type `self.dtype` to an array
        of type `int` with an additional index labeling the
        tuple indeces.

        :param np.ndarray A: An `np.array` of type `self.dtype`.

        :rtype: `np.ndarray`
        """
        # this could be a static method, but we choose to be consistent with
        # from_regular_array
        return A.view((int, len(A.dtype.names))).reshape(A.shape + (-1,))