looking for examples of polymorphism in boost::msm basic state machine

Question

I am new to c++, boost and using state machines. Does anyone know of an example of polymorphic boost::msm state machine?

I tried to change a transition action to virtual in the basic example provided, but the linker says :

undefined reference to `vtable for DerivedClass'

EDIT: Error was a basic and boring include/definition error that was resolved by analyzing the code.

After reading the basic example again carefully, I realized that to make it polymorphic, I should define the back-end in the child classes and inherit from the front-end.

The bellow source files define a Polymorphic basic msm:

• Flower is a dead object with no state
• FlowerMSM is state machine (a way to give MSM behavior to Flower)
• LiveFlower inherits from both and overrides transition actions from FlowerMSM

LiveFlower.cpp

#include "Flower.hpp"
#include "FlowerMSM.hpp"

class LiveFlower: public Flower, public player_ 
{
        void waterAction(evNoWater const&);
        void stopWateringAction(evEnoughWater const&);
};
//Idle
void LiveFlower::waterAction(evNoWater const&)       { std::cout << "Here goes call to LiveFlower::waterAction"; }
//Watering
void LiveFlower::stopWateringAction(evEnoughWater const&)       { std::cout << "Here goes call to LiveFlower::stopWateringAction"; }

typedef msm::back::state_machine<LiveFlower> FonFon;

int main()
{
    FonFon =new FonFon f();
    f.start();
    f.process_event(evNoWater());
}

FlowerMSM.cpp

#include <iostream>
// back-end
#include <boost/msm/back/state_machine.hpp>
//front-end
#include <boost/msm/front/state_machine_def.hpp>
// FlowerMSM is the boost::msm state machine of Flower and defines the logic of its dynamic behavior in response to external events.
namespace msm = boost::msm;
namespace mpl = boost::mpl;


namespace
{

    // events

    struct evNoWater {};
    struct evEnoughWater {};
    // front-end: define the FSM structure 
    struct player_ : public msm::front::state_machine_def<player_>
    {
        template <class Event,class FSM>
        void on_entry(Event const& ,FSM&) 
        {
            std::cout << "entering: Flower Player" << std::endl;
        }
        template <class Event,class FSM>
        void on_exit(Event const&,FSM& ) 
        {
            std::cout << "leaving: Flower Player" << std::endl;
        }

// The list of Flower states
        struct Idle : public msm::front::state<> 
        {
            // every (optional) entry/exit methods get the event passed.
            template <class Event,class FSM>
            void on_entry(Event const&,FSM& ) {std::cout << "Flower entering: Idle" << std::endl;}
            template <class Event,class FSM>
            void on_exit(Event const&,FSM& ) {std::cout << "Flower leaving: Idle" << std::endl;}
        };

        struct Watering : public msm::front::state<> 
        {
            // every (optional) entry/exit methods get the event passed.
            template <class Event,class FSM>
            void on_entry(Event const&,FSM& ) {std::cout << "Flower entering: Watering" << std::endl;}
            template <class Event,class FSM>
            void on_exit(Event const&,FSM& ) {std::cout << "Flower leaving: Watering" << std::endl;}
        };

        // the initial state of the Flower player SM. Must be defined
        typedef Idle initial_state;
        // transition actions

    //Idle
        virtual void waterAction(evNoWater const&)       { std::cout << "Here goes call to Flower::waterAction"; }


    //Watering
        virtual void stopWateringAction(evEnoughWater const&)       { std::cout << "Here goes call to Flower::stopWateringAction"; }

        typedef player_ p; // makes transition table cleaner

        // Transition table for player
        struct transition_table : mpl::vector<
            //    Start     Event         Next      Action               Guard
            //  +---------+-------------+---------+---------------------+----------------------+

          a_row < Idle , evNoWater        , Watering , &p::waterAction                      >,
          a_row < Watering , evEnoughWater        , Idle , &p::stopWateringAction                      >
            //  +---------+-------------+---------+---------------------+----------------------+
        > {};
        // Replaces the default no-transition response.
        template <class FSM,class Event>
        void no_transition(Event const& e, FSM&,int state)
        {
            std::cout << "no transition from state " << state
                << " on event " << typeid(e).name() << std::endl;
        }


    };
    // Pick a back-end
    typedef msm::back::state_machine<player_> FlowerMSM;
}

And for the sake of completeness, the "Dead" Flower class: Flower.hpp

#include <string>
#include <iostream>

class Flower
{
    public:
        Flower();
        Flower(std::string type);
        std::string getType();
        void setType(std::string type);
        void water();
        void stopWatering();
    private:
        std::string typ;
};
Flower::Flower(){}

Flower::Flower(std::string type){typ=type;}
std::string Flower::getType(){return typ;}
void Flower::setType(std::string type){typ=type;}
void Flower::water(){std::cout<<"watering now";}
void Flower::stopWatering(){std::cout<<"stopped watering ";}

EDIT: not accepting my own answer yet in case someone comes with a better solution.

Answer 1

In the original post the answer is now provided.