A write-back version of Trace

        Returns
        -------
        ref : RefTrace
            `ref` is returned in a context manager, and must be in a ``with``
            statement

        Notes
        -----
        .. versionadded:: 1.6

        Examples
        --------
        >>> with trace.ref as ref:
        ...     ref[10] += 1.617

def ref(self):
        """
        A write-back version of Trace

        Returns
        -------
        ref : RefTrace
            `ref` is returned in a context manager, and must be in a ``with``
            statement

        Notes
        -----
        .. versionadded:: 1.6

        Examples
        --------
        >>> with trace.ref as ref:
        ...     ref[10] += 1.617
        """

        x = RefTrace(self.filehandle,
                     self.dtype,
                     len(self),
                     self.shape,
                     self.readonly,
                    )
        yield x
        x.flush()