[Boost-users] [1.44 MSM meta state machine] accessing objects from actions

Subject: [Boost-users] [1.44 MSM meta state machine] accessing objects from actions
From: Hajo Kirchhoff (mailinglists_at_[hidden])
Date: 2010-10-25 03:39:00

Hi all,
what is the recommended way to use objects with an MSM state machine?

I've written a state machine that handles sending data via UDP (asio).
I'm using the functor front end and I have a 'send' action:
struct a_send
{
  template <typename Event, typename Fsm, typename S, typename T>
  void operator()(Event const& evt, Fsm &fsm, S&, T&)
  {
        // get next object from queue and post it to asio
  }
};

My question is, how are actions supposed to access the objects that the
state machine should work with?

Currently my queue object is a member of the state machine itself, so I
can write

struct Send_ : public msm::front::state_machine_def<Send_>
{
  string m_next_line_to_send;
  socket m_socket;
  string get_next_send_line();
};

and in my a_send action
  void operator()(Event &const &evt, Fsm &fsm, S&, T&)
  {
    fsm.m_next_line_to_send=fsm.get_next_send_line();
    fsm.m_socket.async_write(fsm.m_next_line_to_send);
  }

This works well as long as I am not using sub-statemachines.

Here is my problem:
I would like to use a substate machine for the actual sending. The main
state machine has the states Disconnected, Working, Error, Shutdown. The
Working state should actually be a substate machine.

The problem is, when a_send gets called by the substate machine Working,
the fsm object is of type Working.

How can I access the member variables of the parent of a substate
machine? Or is there a better way of accessing the objects the state
machine should work with from actions?

The tutorial explains state machines very nicely with the example of a
CD player. But all the actions are empty and nowhere is explained, how
you would actually access a CD player member variable or other such
object so that you could actually manipulate the player to do something.

Regards and thanks

Hajo