Is there a way to get message tag?

[fishTsai20]

get message tag by c++ like below: https://github.com/dungeon-master-666/ton/blob/200508cf8fca3ce5aa8d566105e32aea38601e93/crypto/tl/tlblib.hpp#L723

auto message_cs = vm::load_cell_slice(trans.r1.in_msg->prefetch_ref());
block::gen::t_CommonMsgInfo.get_tag(message_cs)

  int get_tag(const vm::CellSlice& cs) const override {
    return cs.bselect(2, 13);
  }

How to get tag by your code?