def size(self, index: int):
        """
        Return an example's size as a float or tuple. Here we return the max
        across all underlying datasets. This value is used when filtering a
        dataset with max-positions.
        """
        return max(
            dataset.size(self._map_index_to_dataset(key, index))
            for key, dataset in self.datasets.items()
        )

        Return an example's size as a float or tuple. Here we return the max
        across all underlying datasets. This value is used when filtering a
        dataset with max-positions.
        
understand_icl/fairseq/fairseq/data/multi_corpus_sampled_dataset.py