// In header: <boost/log/utility/setup/formatter_parser.hpp>
template<typename CharT> 
struct formatter_factory {
  // types
  typedef CharT                                char_type;       // Character type. 
  typedef std::basic_string< char_type >       string_type;     // String type. 
  typedef basic_formatter< char_type >         formatter_type;  // The formatter function object. 
  typedef std::map< string_type, string_type > args_map;      
  // construct/copy/destruct
  formatter_factory() = default;
  formatter_factory(formatter_factory const &) = delete;
  formatter_factory & operator=(formatter_factory const &) = delete;
  ~formatter_factory();
  // public member functions
  virtual formatter_type 
  create_formatter(attribute_name const &, args_map const &) = 0;
};