Chris Knight wrote:
On Tuesday 05 August 2008 4:34:30 pm David Abrahams wrote:
The finite state machine I came up with for the FIX protocol was well over 50 transitions. I implemented ours so that the from state could be boost::any which acts acts like '.' in regexps and I suppose means our implementation should be renamed kmt::nfsm. It was a zero-cost implentation as it simply adds one last transition to each from state's action linked-list.I was able to get the transition list down to 22 with that one feature. Mostly all the different error conditions that you want to handle gracefully in a text protocol originally designed in the 1980's and still used by finance exchanges today. <sigh>
The Boost.FSM library supports similar feature. You can use any_state placeholder in transitions in order to tell that the transition works for any source state.
The other feature that I'm not sure whether FSM supports or not is static registering of posted event types so as to skip around run-time double dispatching. I suspect any implementation that seeks to provide a simplified/speedier interface over StateChart should support that as well.
I'm not sure what you mean by that "registering". The library does one event dispatching if it is known at compile time that no entry in the transition map will be triggered. If a transition map entry is triggered, then two dispatches are done - one to deliver event to the transition handler, and second to deliver the event to the active state. In any case, dispatching is very efficient and is basically a call on a function pointer that is acquired from an array by index.