[Boost-users] Accessing MSM attribute under specific conditions causes non-compile

Subject: [Boost-users] Accessing MSM attribute under specific conditions causes non-compile
From: Chiem Whua Ma (boost.reg_at_[hidden])
Date: 2012-09-01 03:22:56

 This is my first post to the list.  I've been working with MSM and have
been pulling my hair out over what I now think is a bug, either in the
library or the compiler.

If you create an action, and inside that action you do a get_attribute on
the state machine, and that state machine (MSM) is a sub-statemachine of
another (parent) MSM, and that sub-machine state happens to be the initial
state of the parent machine (that's a lot of ifs!), the code will not
compile.  It aborts with the mysterious error:

c:\boost_1_51_0\boost\fusion\container\map\detail\deref_data_impl.hpp(28):
error C2039: 'second_type' : is not a member of 'boost::mpl::void_'

followed by the traditional slew of other stuff.

Although this example is easy enough to work around, I've found whether it
works or not is erratic.  The one thing that seems to work OK is to move
the action out of the entry for the sub machine and into the entry of the
first state, but I haven't done enough testing to show that this works.

I've attached a zip and included the text of a sample.  As is it will not
compile.  You can either uncomment the attribute assignment or change the
initial state to make it compile.

Any help with this would be appreciated!  Thanks!

-Chiem

Here's sample code.  I've also attached a zip:

#include <vector>
#include <iostream>

#include <boost/msm/back/state_machine.hpp>
#include <boost/msm/front/euml/euml.hpp>

using namespace std;
using namespace boost::msm::front::euml;
namespace msm = boost::msm;

namespace MSM_A // Concrete FSM implementation
{
    BOOST_MSM_EUML_DECLARE_ATTRIBUTE(int, borrowedBuffer_attribute);

    BOOST_MSM_EUML_ACTION(someAction)
    {
        template <class Event,class FSM,class STATE>
        void operator()(Event const& event,FSM& fsm, STATE&)
        {
            fsm.get_attribute(borrowedBuffer_attribute)=1;        //
<--------------- UNCOMMENTING THIS WILL ALSO ALLOW COMPILATION
        }
    };

    BOOST_MSM_EUML_EVENT(someevent)

    BOOST_MSM_EUML_STATE((no_action), someStateA)
    BOOST_MSM_EUML_STATE((no_action), someStateB)

    BOOST_MSM_EUML_TRANSITION_TABLE((
          someStateA + someevent == someStateB
          ),transition_table)

    BOOST_MSM_EUML_DECLARE_STATE_MACHINE(( transition_table,
                                    init_ << someStateA,
                                    someAction,  // <--------------------
ACTION IS AN ENTRY ACTION
                                    no_action,
                                    attributes_ << borrowedBuffer_attribute,
                                    configure_ << no_configure_
                                    ),
                                    MSM_A_frontEnd) //fsm name
    typedef msm::back::state_machine<MSM_A_frontEnd> MSM_A_player;
}

namespace MSM_B // Concrete FSM implementation
{
    ::MSM_A::MSM_A_player subMachine;
    BOOST_MSM_EUML_EVENT(someEvent)
    BOOST_MSM_EUML_STATE((no_action), someState)
    BOOST_MSM_EUML_TRANSITION_TABLE((
        someState + someEvent == subMachine
    ), transition_table)
    BOOST_MSM_EUML_DECLARE_STATE_MACHINE((    transition_table, //STT
                                            //init_ << someState, //
<---------------- WORKS
                                            init_ << subMachine, //
<---------------- DOES NOT COMPILE
                                            no_action, // Entry
                                            no_action, // Exit
                                            attributes_ << no_attributes_,
// Attributes
                                            configure_ << no_configure_
                                            ),
                                            MSM_B_frontEnd) //fsm name

    typedef msm::back::state_machine<MSM_B_frontEnd> MSM_B_player;
}

int main()
{

    MSM_B::MSM_B_player player;
    player.start();
    return 0;
}