#include <boost/sml.hpp> namespace sml = boost::sml;

struct sender { template<class TMsg> constexpr void send(const TMsg& msg) { std::printf("send: %d\n", msg.id); } };

struct ack { bool valid{}; }; struct fin { int id{}; bool valid{}; }; struct release {}; struct timeout {};

constexpr auto is_valid = [](const auto& event) { return event.valid; };

constexpr auto send_fin = [](sender& s) { s.send(fin{0}); }; constexpr auto send_ack = [](const auto& event, sender& s) { s.send(event); };

struct tcp_release { auto operator()() const { using namespace sml; /**  * Initial state: *initial_state  * Transition DSL: src_state + event [ guard ] / action = dst_state  */ return make_transition_table( *"established"_s + event<release> / send_fin = "fin wait 1"_s, "fin wait 1"_s + event<ack> [ is_valid ] = "fin wait 2"_s, "fin wait 2"_s + event<fin> [ is_valid ] / send_ack = "timed wait"_s, "timed wait"_s + event<timeout> = X ); } };

int main() { using namespace sml; sender s{}; sm<tcp_release> sm{s}; // pass dependencies via ctor assert(sm.is("established"_s)); sm.process_event(release{}); // complexity O(1) assert(sm.is("fin wait 1"_s)); sm.process_event(ack{true}); // prints 'send: 0' assert(sm.is("fin wait 2"_s)); sm.process_event(fin{42, true}); // prints 'send: 42' assert(sm.is("timed wait"_s)); sm.process_event(timeout{}); assert(sm.is(X)); // terminated }