Method num_cols

cpp/src/arrow/acero/schema_util.h:79–82

  }

  int num_cols(ProjectionIdEnum schema_handle) const {
    int id = schema_id(schema_handle);
    return static_cast<int>(schemas_[id].second.data_types.size());
  }

  bool is_empty(ProjectionIdEnum schema_handle) const {
    return num_cols(schema_handle) == 0;