State machines without default constructors in boost:msm

Question

In the documentation for boost::msm there is an example of a state machine without a default constructor. I can get it to work where I jump directly from a super-SM into a sub-SM. But when I jump from one sub-SM into another sub-SM the target SM is default constructed and my data is gone. Below is an example. I can't get it to compile without providing default constructors for the sub states. Do I need to provide some extra info in my sub-SMs for this to work?

When I run the example I get:

Jumping directly to Sub1
Sub1.data_ = 0x7fff5fbfd778
Jumping directly to Sub2
Sub2.data_ = 0x7fff5fbfd778
Jumping from Sub1 to Sub2
Sub1.data_ = 0x7fff5fbfd778
Sub2.data_ = 0xdeadbeef

I expected the 0xdeadbeef to be the same address as the others.

#include <iostream>
#include <boost/msm/back/state_machine.hpp>
#include <boost/msm/front/state_machine_def.hpp>
#include <boost/msm/front/functor_row.hpp>

namespace {

    using namespace boost::msm;
    using namespace boost::msm::front;
    namespace mpl = boost::mpl;

    struct MyData {
        int data;
    };

    struct EvGotoSub1 {};
    struct EvGotoSub2 {};

    struct MainSM_;
    using Main = back::state_machine<MainSM_>;    
    struct Sub1SM_;
    using Sub1 = back::state_machine<Sub1SM_>;
    struct Sub2SM_;
    using Sub2 = back::state_machine<Sub2SM_>;

    struct Sub1SM_ : state_machine_def<Sub1SM_> {
        struct Started : state<> {
            template <class Event,class Fsm>
            void on_entry(Event const& e, Fsm& fsm) {
                std::cout << "Sub1.data_ = " << (void*) fsm.data_ << std::endl;
            }
        };
        using initial_state = mpl::vector<Started>;
        struct transition_table:mpl::vector<
        Row<Started, EvGotoSub2, Sub2, none, none>
        > {};
        MyData* data_;

        Sub1SM_() : data_((MyData*) 0xdeadbeef) {};
        Sub1SM_(MyData* data) : data_(data) {};
    };

    struct Sub2SM_ : state_machine_def<Sub2SM_> {
        struct Started : state<> {
            template <class Event,class Fsm>
            void on_entry(Event const& e, Fsm& fsm) {
                std::cout << "Sub2.data_ = " << (void*) fsm.data_ << std::endl;
            }
        };
        using initial_state = mpl::vector<Started>;
        struct transition_table:mpl::vector<
        //Row<Started, EvGotoSub1, Sub1, none, none>
        > {};
        MyData* data_;

        Sub2SM_() : data_((MyData*) 0xdeadbeef) {};
        Sub2SM_(MyData* data) : data_(data) {};
    };

    struct MainSM_ : state_machine_def<MainSM_> {
        struct Started : state<> {};
        using initial_state = mpl::vector<Started>;
        struct transition_table:mpl::vector<
        Row<Started, EvGotoSub1, Sub1, none, none>,
        Row<Started, EvGotoSub2, Sub2, none, none>
        > {};
        MyData* data_;

        MainSM_(MyData* data) : data_(data) {};
    };
}

int main() {
    MyData data { 123 };

    auto CreateMain = [&data] {
        auto ret = Main(back::states_ << Sub1(&data) << Sub2(&data), &data);
        ret.start();
        return ret;
    };

    std::cout << "Jumping directly to Sub1" << std::endl;
    Main main = CreateMain();
    main.process_event(EvGotoSub1());

    std::cout << "Jumping directly to Sub2" << std::endl;
    main = CreateMain();
    main.process_event(EvGotoSub2());

    std::cout << "Jumping from Sub1 to Sub2" << std::endl;
    main = CreateMain();
    main.process_event(EvGotoSub1());
    main.process_event(EvGotoSub2());        
}

Answer 1

The default constructor must be defined. For Sub1 you must specify as well which constructor of Sub2 you want to use:

auto ret = Main(back::states_ << Sub1(back::states_ << Sub2(&data), &data) << Sub2(&data), &data);

This outputs:

Jumping directly to Sub1
Sub1.data_ = 0xbfe82bf0
Jumping directly to Sub2
Sub2.data_ = 0xbfe82bf0
Jumping from Sub1 to Sub2
Sub1.data_ = 0xbfe82bf0
Sub2.data_ = 0xbfe82bf0

live example: https://ideone.com/XMtDye