4 ms·

State machines don't have syntax for "transition here when event is encountered no matter what state you are in" so the whole diagram becomes a spaghetti mess i

State machines don't have syntax for "transition here when event is encountered no matter what state you are in" so the whole diagram becomes a spaghetti mess if you have a lot of those escape hatches.

a_t48 2y ago
I believe HSMs can model this, but don't quote me. :)
- nurettin 2y ago
  Yes, of course in theory nested state machines should be able to model this. I feel like adding more complexity and bending the rules is a bit of a concession.
  - jeffreygoesto 2y ago
    Back in the days we implemented HSM helper classes in about 500 LoC and generated them from Enterprise Architect. No need to write a GUI yourself, but better to have a visual for documentation and review. Worked very well until we replaced EA with docs-as-code, now I miss that there is no nice simulator and Modeler for that workflow.
quietbritishjim 2y ago
State machines don't have a native syntax in C++ at all, so you can structure them however you want. It's easy to structure a state machine, if needed, so that all (or some) states can handle the same event in the same way.
- garethrowlands 2y ago
  Switch + goto is very close to being a native syntax for state machines. It's also very efficient.
- dgfitz 2y ago
  I always thought this framework was neat: https://doc.qt.io/qt-5/statemachine-api.html https://doc.qt.io/qt-5/statemachine-api.html Downside of course is now you have a dependency on qt.
  - alexvitkov 2y ago
    The downside is that you're now heap allocating at least one object for every state, and I'm willing to bet that each QState has an associated std::vector-style list of actions, and that each action is also its own object on the heap. If you can afford to do things like this you can most likely use something other than C++ and save yourself a lot of headaches.
    - dgfitz 2y ago
      > If you can afford to do things like this you can most likely use something other than C++ and save yourself a lot of headaches. Surely you can understand that, despite the recent c++ hate, my job doesn't give a fuck and we aren't migrating our massive codebase from c++ to... anything.
liontwist 2y ago
goto is exactly this feature.
lelanthran 2y ago
> State machines don't have syntax for "transition here when event is encountered no matter what state you are in" so the whole diagram becomes a spaghetti mess if you have a lot of those escape hatches. I place a note at the top of my diagrams stating what the default state would be on receipt of an unexpected event. There is no such thing as "event silently gets swallowed because no transition exists", because, in implementation, the state machine `switch` statement always has a `default` clause which triggers all the alarm bells. Works very well in practice; I used to write hard real-time munitions control software for blowing shit up. Never had a problem.
- rramadass 2y ago
  > hard real-time munitions control software for blowing shit up. Never had a problem. Ha, Ha, Ha! The juxtaposition of these two phrases is really funny. I would like to apply for a position on the Testing team :-)
  - lelanthran 2y ago
    > Ha, Ha, Ha! The juxtaposition of these two phrases is really funny. I would like to apply for a position on the Testing team :-) It had its moments: used to go to a range where we'd set off detonators. Once or twice in production on site where we'd set off actual explosives.

a_t48 2y ago

I believe HSMs can model this, but don't quote me. :)

nurettin 2y ago
Yes, of course in theory nested state machines should be able to model this. I feel like adding more complexity and bending the rules is a bit of a concession.
- jeffreygoesto 2y ago
  Back in the days we implemented HSM helper classes in about 500 LoC and generated them from Enterprise Architect. No need to write a GUI yourself, but better to have a visual for documentation and review. Worked very well until we replaced EA with docs-as-code, now I miss that there is no nice simulator and Modeler for that workflow.

quietbritishjim 2y ago

State machines don't have a native syntax in C++ at all, so you can structure them however you want. It's easy to structure a state machine, if needed, so that all (or some) states can handle the same event in the same way.

garethrowlands 2y ago
Switch + goto is very close to being a native syntax for state machines. It's also very efficient.
dgfitz 2y ago
I always thought this framework was neat: https://doc.qt.io/qt-5/statemachine-api.html https://doc.qt.io/qt-5/statemachine-api.html Downside of course is now you have a dependency on qt.
- alexvitkov 2y ago
  The downside is that you're now heap allocating at least one object for every state, and I'm willing to bet that each QState has an associated std::vector-style list of actions, and that each action is also its own object on the heap. If you can afford to do things like this you can most likely use something other than C++ and save yourself a lot of headaches.
  - dgfitz 2y ago
    > If you can afford to do things like this you can most likely use something other than C++ and save yourself a lot of headaches. Surely you can understand that, despite the recent c++ hate, my job doesn't give a fuck and we aren't migrating our massive codebase from c++ to... anything.

liontwist 2y ago

goto is exactly this feature.

lelanthran 2y ago

> State machines don't have syntax for "transition here when event is encountered no matter what state you are in" so the whole diagram becomes a spaghetti mess if you have a lot of those escape hatches. I place a note at the top of my diagrams stating what the default state would be on receipt of an unexpected event. There is no such thing as "event silently gets swallowed because no transition exists", because, in implementation, the state machine `switch` statement always has a `default` clause which triggers all the alarm bells. Works very well in practice; I used to write hard real-time munitions control software for blowing shit up. Never had a problem.

rramadass 2y ago
> hard real-time munitions control software for blowing shit up. Never had a problem. Ha, Ha, Ha! The juxtaposition of these two phrases is really funny. I would like to apply for a position on the Testing team :-)
- lelanthran 2y ago
  > Ha, Ha, Ha! The juxtaposition of these two phrases is really funny. I would like to apply for a position on the Testing team :-) It had its moments: used to go to a range where we'd set off detonators. Once or twice in production on site where we'd set off actual explosives.