What compiler is he/she using? I cannot get this to compile at all but I might not know the magic compiler incantation to get it to work.

  template<typename T>
  auto length(const T& value) noexcept {
      if constexpr (std::integral<T>::value) { // is number
          return value;
      }
      else {
          return value.length();
      }
  }