fast std::string concat c++

concat.h

//originally it was written on 

template <class... S>
std::string concat(const S&... strs) {
  std::string_view views[]{strs...};
  int totalsize = std::accumulate(std::begin(views), std::end(views), 0, [](int count, std::string_view v){return count + v.size();});
  std::string result(totalsize, '\0');
  int cur_pos = 0;
  for(const auto& v : views){
    std::copy(v.begin(), v.end(), result.begin() + cur_pos);
    cur_pos += v.size();
  }
  assert(cur_pos == totalsize);
  return result;
}