Can a boost::sml state machine with policies be copied?

Question

From https://boost-ext.github.io/sml/examples.html#deferprocess

Modified to try and copy the fsm.

#include <boost/sml.hpp> #include <cassert> #include <deque> #include <queue> namespace sml = boost::sml; namespace { struct e1 {}; struct e2 {}; struct e3 {}; struct e4 {}; struct defer_and_process { auto operator()() const noexcept { using namespace sml; return make_transition_table( *"idle"_s + event<e1> / defer , "idle"_s + event<e2> = "s1"_s , "s1"_s + event<e1> / process(e2{}) = "s2"_s , "s2"_s + event<e3> / process(e4{}) , "s2"_s + event<e4> = X ); } }; } // namespace int main() { using namespace sml; boost::sml::sm<defer_and_process, sml::defer_queue<std::deque>, sml::process_queue<std::queue>> sm; /// defer_queue policy to enable deferred events using std::queue boost::sml::sm<defer_and_process, sml::defer_queue<std::deque>, sml::process_queue<std::queue>> secondSm; sm = secondSm; }

Copies fine without policies. Is there a trick to it?

If not, then how can the fsm ever be put into a class, seeing how it's a c++ library? Pointers? But those are on the heap.

I apparently cannot. I'm not sure why not. Regardless, it's not a problem to store it in a class at all. The containing class will just not be copyable. unique_ptr<SM> to make it movable or shared_ptr<SM> to make it copyable. Of course, none of that make the SM actually copy. I'd refer to the library devs to find out about whether that's by design — sehe
– sehe, Commented Apr 21 at 22:05
Then maybe I have asked the wrong question. Cause without a copy then I don't know how to make an instance of the fsm later when all dependencies are finished, give them it, and then overwrite the fsm with that. — DrDreadful
– DrDreadful, Commented Apr 21 at 22:45
Yes, there's no way, unless there's another documented way to clone. Again, I'd file the issue on github — sehe
– sehe, Commented Apr 21 at 22:54
I'll get to that, yeah. Maybe ask if it's possible to inject dependencies later, too. I think this library might be for things like firmware and other such things, though, and not really general stuff. — DrDreadful
– DrDreadful, Commented Apr 21 at 23:06

DrDreadful · Accepted Answer · 2025-04-21 23:10:20Z

1

Apparently it is not possible.

answered Apr 21 at 23:10

DrDreadful

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