Function mutable_offsets

cpp/src/arrow/compute/row/row_internal.h:228–231

    return reinterpret_cast<const offset_type*>(data(1));
  }
  offset_type* mutable_offsets() {
    ARROW_DCHECK(!metadata_.is_fixed_length);
    return reinterpret_cast<offset_type*>(mutable_data(1));
  }

  const uint8_t* var_length_rows() const {
    ARROW_DCHECK(!metadata_.is_fixed_length);