Evaluates and accumulates evaluation metric on outputs of the last forward computation.

        Parameters
        ----------
        eval_metric : EvalMetric
        labels : list of NDArray
            Typically ``data_batch.label``.

def update_metric(self, eval_metric, labels, pre_sliced=False):
        """Evaluates and accumulates evaluation metric on outputs of the last forward computation.

        Parameters
        ----------
        eval_metric : EvalMetric
        labels : list of NDArray
            Typically ``data_batch.label``.
        """
        assert self.binded and self.params_initialized
        self._curr_module.update_metric(eval_metric, labels, pre_sliced)