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How to reuse code (a Guard) defined in a submachine in the parent SM (using boost-msm)?

I've defined a guard in a sub-state machine and now I want to use the exact logic/guard in the parent SM (using boost-msm). using the same guard in the transition_table results in compilation error: unknown type name 'GuardSS'.

I've defined the guard (and its corresponding value) in the sub-machine, but it can be moved to the parent SM if it helps in solving the problem and allows me to reuse the guard.

A sample code can be found here.

How can I reuse the code used in the guard?

Code included:

#include <iostream>
#include "myfsm.h"

int main()

std::cout << "Testing boost::msm ..." << std::endl;
MyFsm fsm;
fsm.start();

fsm.process_event(Event12());

fsm.process_event(Event_ss12());

//guard valu changes
MyFsm_::State2 &state = fsm.get_state<MyFsm_::State2&>();
state.m_guardVal = true;

fsm.process_event(Event_ss12());

fsm.process_event(Event21());//?protect this transition using the same Guard



fsm.h:

#ifndef MYFSM
#define MYFSM

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

struct Event12;
struct Event21;
struct Event_ss12;
struct Event_ss21;

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

struct MyFsm_ : msmf::state_machine_def<MyFsm_>

struct State1 : msmf::state<>
template<class Event, class Fsm> void on_entry(const Event&, Fsm&) const std::cout << "State1::on_entry()" << std::endl;
template<class Event, class Fsm> void on_exit(const Event&, Fsm&) const std::cout << "State1::on_exit()" << std::endl;
;

struct State2_ : msmf::state_machine_def<State2_>
template <class Event,class Fsm> void on_entry(Event const&, Fsm&) const std::cout << "State2::on_entry()" << std::endl;
template <class Event,class Fsm> void on_exit(Event const&, Fsm&) const std::cout << "State1::on_exit()" << std::endl;

struct SubState1 : msmf::state<>
template <class Event,class Fsm> void on_entry(Event const&, Fsm&) const std::cout << "SubState1::on_entry()" << std::endl;
template <class Event,class Fsm> void on_exit(Event const&, Fsm&) const std::cout << "SubState1::on_exit()" << std::endl;
;
struct SubState2 : msmf::state<>
template <class Event,class Fsm> void on_entry(Event const&, Fsm&) const std::cout << "SubState2::on_entry()" << std::endl;
template <class Event,class Fsm> void on_exit(Event const&, Fsm&) const std::cout << "SubState2::on_exit()" << std::endl;
;
// Guards
struct GuardSS
template <class Event, class Fsm, class SourceState, class TargetState>
bool operator()(Event const&, Fsm& fsm, SourceState&, TargetState&)

if (fsm.m_guardVal == true)
std::cout << "Transition Approved by Guard n";
return true;

std::cout << "Transition Rejected by Guard n";
return false;

;
typedef SubState1 initial_state;

struct transition_table:mpl::vector<
// Start Event Next Action Guard
msmf::Row < SubState1, Event_ss12, SubState2, msmf::none, GuardSS >,
msmf::Row < SubState2, Event_ss21, SubState1, msmf::none, msmf::none >
> ;

bool m_guardVal=false;
;
typedef msm::back::state_machine<State2_> State2;

// Set initial state
typedef State1 initial_state;

// Transition table
struct transition_table:mpl::vector<
msmf::Row < State1, Event12, State2, msmf::none, msmf::none >,
msmf::Row < State2, Event21, State1, msmf::none, GuardSS/*msmf::none*/ >
>;

template<class Event, class Fsm>
void no_transition(Event const&, Fsm&, int state)
std::cout<<"no_transiton detected from state: "<< state << std::endl;


;
// Pick a back-end
typedef msm::back::state_machine<MyFsm_> MyFsm;


#endif // MYFSM


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