// In header: <boost/log/expressions/attr.hpp>
template<typename T, typename FallbackPolicyT, typename TagT, 
         template< typename > class ActorT> 
class attribute_actor :
  public ActorT< attribute_terminal< T, FallbackPolicyT, TagT > >
{
public:
  // types
  typedef TagT                                                               tag_type;              // Attribute tag type. 
  typedef FallbackPolicyT                                                    fallback_policy;       // Fallback policy. 
  typedef attribute_terminal< T, fallback_policy, tag_type >                 terminal_type;         // Base terminal type. 
  typedef terminal_type::value_type                                          value_type;            // Attribute value type. 
  typedef ActorT< terminal_type >                                            base_type;             // Base actor type. 
  typedef attribute_actor< value_type, fallback_to_none, tag_type, ActorT >  or_none_result_type;   // Expression with cached attribute name. 
  typedef attribute_actor< value_type, fallback_to_throw, tag_type, ActorT > or_throw_result_type;  // Expression with cached attribute name. 
  // construct/copy/destruct
  explicit attribute_actor(base_type const &);
  // public member functions
  attribute_name get_name() const;
  fallback_policy const & get_fallback_policy() const;
  or_none_result_type or_none() const;
  or_throw_result_type or_throw() const;
  template<typename DefaultT> 
    attribute_actor< value_type, fallback_to_default< DefaultT >, tag_type, ActorT > 
    or_default(DefaultT const &) const;
};