New API in libsigc++ 3.4

Member sigc::track_object (const T_functor & func, const T_obj1 & obj1, const T_objs &... objs)

Class sigc::trackable_signal< T_return(T_arg...)>

Class sigc::trackable_signal< T_return(T_arg...)>::accumulated< T_accumulator >

Class sigc::trackable_signal_with_accumulator< T_return, T_accumulator, T_arg >