Johan Nilsson wrote:
1. For a state, is it possible to specify a method that will be called when an event with no defined handlers is received?
Interesting question. Can all events inherit from a common base class, to which a state could define a (default) reaction, and override this with reactions to specific event sub-classes?
2. Is is somehow possible to reuse state definitions as substates of different "higher-level" states?
In boost/libs/statechart/doc/tutorial.html#TransitionActions it says, "With Boost.Statechart, a transition action can be a member of any common outer context" and goes on to give some examples. If I've understood your question correctly then the answer is "Yes".
- I've got an application that can be either in remote or locally controlled mode (this is the highest-level states). - Certain events are allowed both in remote and local, while some are not. As an example, the "CommandEvent" event should be handled both in remote and local - resulting in the "ExecutingCommandState" being entered. - I'd like to be able to reuse the definition of ExecutingCommandState regardless of the enclosing state being Remote or Local - Possible?
Could you implement this with orthogonal regions? Top Remote Local ------ Idle Executing Here the top state contains two orthogonal regions separated by a dashed line. The only problem here is that actions (in transitions from say Idle) that need to be different depending on whether it's in Remote or Local gain conditional logic. (If that's all Remote and Local are used for they could just be replaced by a bool member of Top.) If you had Top Remote RIdle RExecuting Local LIdle LExecuting you'd avoid this, at the expense of possibly repeating code in the (only slightly different) actions of a transition originating from either RIdle or LIdle. This common code could perhaps be extracted into a method belonging to the shared super-state, Top. This sounds like a similar problem to the one I face. Where are you planning to execute the command? In my application the commands take a long time, so are not suitable for implementing as an action. UML provides "Do Activities" that can be used for this purpose. The statechart docs suggest simulating this "with a separate thread that is started in the entry action and canceled (!) in the exit action of a particular state". I quite like that approach. Yours, Tim Milward