template<typename Signature> 
class storage_modifier {
public:
  // types
  typedef boost::function_types::parameter_types< Signature >::type   parameter_types;
  typedef unspecified                                                 storable_types; 
  typedef boost::fusion::result_of::as_vector< storable_types >::type storable_vector;
  template<typename S, typename T1> 
  struct result<storage_modifier< S >(const T1 &)> {
    // types
    typedef boost::optional< const T1 & > type;
  };

  // construct/copy/destruct
  storage_modifier(bool = true);
  storage_modifier(const storage_modifier &);
  template<typename Seq> storage_modifier(const Seq &, bool = true);

  // public member functions
  const storable_vector & stored_vector() ;
  void open() ;
  void close() ;
};