Function mutable_fixed_length_rows

cpp/src/arrow/compute/row/row_internal.h:219–222

    return data(1) + static_cast<int64_t>(row_id) * metadata_.fixed_length;
  }
  uint8_t* mutable_fixed_length_rows(uint32_t row_id) {
    ARROW_DCHECK(metadata_.is_fixed_length);
    return mutable_data(1) + static_cast<int64_t>(row_id) * metadata_.fixed_length;
  }

  const offset_type* offsets() const {
    ARROW_DCHECK(!metadata_.is_fixed_length);