Bohdan, > Ooops, sorry ... i was terribly unclear. > > Andreas Huber wrote: > "boost::fsm no longer uses acyclic visitor! The current double > dispatch implementation (which was inspired by Aleksey's fsm lib) > uses one virtual call followed by a linear search for a suitable > reaction, using one RTTI comparison per visited reaction. Although > you cannot change the double dispatch implementation itself, you can > change one aspect of it, i.e. RTTI." > > I mean : > Where can i find something about cool "double dispatch" used in > recently submitted FSM code ? > Or Aleksey's fsm lib sources ?
You can find Aleksey's fsm lib here: http://www.mywikinet.com/mpl/fsm_example_25_jul_02.zip In my library, you can look for simple_state::react_impl() which is the override for the abstract state_base::react_impl(). The implementation is quite simple: all reactions are contained in an mpl::list, which is passed to a function. The function then calls the front reaction. If the reaction returns that there was a match the result is returned. Otherwise, the function calls itself again with the front of the list removed. Of course, there is a specialisation for an empty list which does nothing. BTW, this double dispatch variant is only "cool" ;-) for cases where the second stage of the double dispatch has to choose from only a few different possibilities. That's because the second stage performs a linear search. In contrast to GOF-visitor, which is essentially constant-time, this variant becomes slower the more choices it has in the second stage. But it scales much better in terms of dependencies. Regards, Andreas _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
