  static std::string&& dna_to_upper_case(std::string& unpacked_dna_sequence) {     std::string ret;     std::for_each(unpacked_dna_sequence.cbegin(),                   unpacked_dna_sequence.cend(),                   [&ret](char c) { ret.push_back(std::toupper(c)); });      return std::move(ret); 