// In header: <boost/log/sinks/attribute_mapping.hpp>

template<typename CharT, typename MappedT> 
struct basic_mapping :
  public std::unary_function< basic_attribute_values_view< CharT >, MappedT >
{
  // types
  typedef CharT                                    char_type;         // Char type. 
  typedef std::basic_string< char_type >           string_type;       // String type. 
  typedef basic_attribute_values_view< char_type > values_view_type;  // Attribute values view type. 
  typedef MappedT                                  mapped_type;       // Mapped value type. 
};