if (a.at(i).has_index() && a.at(i).index() == b.at(i).index()) {
          matches += 1;
        }
        break;
      case ::tensorflow::proto_splitter::FieldIndex::KindCase::kMapKey:
        if (a.at(i).has_map_key()) {
          const ::tensorflow::proto_splitter::FieldIndex_MapKey& key =
              b.at(i).map_key();
          const ::tensorflow::proto_splitter::FieldIndex_MapKey& chunked_key =
              a.at(i).map_key();