Class not_isempty

external/include/backward/backward.hpp:3784–3789

  // and define this one here because C++98 is not happy with local defined
  // struct passed to template functions, fuuuu.
  struct not_isempty {
    bool operator()(const lines_t::value_type &p) {
      return !(std::find_if(p.second.begin(), p.second.end(), not_isspace()) ==
               p.second.end());
    }
  };

  void swap(SourceFile &b) { _file.swap(b._file); }