Method operator()

cpp/src/arrow/array/diff.cc:804–807

      using UnionImpl::UnionImpl;

      void operator()(const Array& array, int64_t index, std::ostream* os) {
        const auto& union_array = checked_cast<const DenseUnionArray&>(array);
        DoFormat(union_array, index, union_array.raw_value_offsets()[index], os);
      }
    };

    std::vector<Formatter> field_formatters(t.max_type_code() + 1);