// In header: <boost/log/sinks/attribute_mapping.hpp>
template<typename MappedT, typename AttributeValueT = int> 
class basic_custom_mapping :
  public boost::log::sinks::basic_mapping< MappedT >
{
public:
  // types
  typedef AttributeValueT        attribute_value_type;  // Attribute contained value type. 
  typedef base_type::mapped_type mapped_type;           // Mapped value type. 
  // construct/copy/destruct
  explicit basic_custom_mapping(attribute_name const &, mapped_type const &);
  // public member functions
  mapped_type operator()(record_view const &) const;
  implementation_defined operator[](attribute_value_type const &);
};