Re: [boost] boost [msm] deferring event by base type.

25 Jun 2010

      On 25 June 2010 12:59, Juraj Ivančić <juraj.ivancic@gmail.com> wrote:
...
On 25.6.2010 10:40, Richard Szabo wrote:
...
I'm now using Row and Defer functor I have now an other problem whit the :
    void defer_event(Event const&  e)
    {
        // to call this function, you need either a state with a
deferred_events typedef
        // or that the fsm provides the activate_deferred_events typedef
        BOOST_MPL_ASSERT(( has_fsm_deferred_events<library_sm>  ));
        execute_return (library_sm::*pf) (Event const&  evt)=
&library_sm::process_event;
        Event temp (e);
        ::boost::function<execute_return ()>  f= ::boost::bind(pf,
this,temp);
        post_deferred_event(f);
    }
actually it tries to instantiate the base class ( Event temp (e); )
but in my case the base class is an abstract class ->  compiler error;
and after deferring I want to dispatch the original derived event not
the copy constructed base class instance of the event.
You might try the following:
Instead of making your event class polymorphic, you add a shared pointer to
polymorphic data. E.g.
struct deferred_event
{
   boost::shared_ptr<deferred_event_data_base> event_data;
};
I don't understand how this would help me with the differing based on
base type ?

Can you please provide a little example based on something like this ?

  struct BaseEvent
  {
    virtual ~BaseEvent() = 0;
  };

BaseEvent::~BaseEvent() {}

struct AEvent : public BaseEvent
{
};

struct BEvent : public BaseEvent
{
};

will not compile :
Row < State1, BaseEvent, none, Defer, none  >

you suggesting  :

struct deferred_event
{
    boost::shared_ptr<BaseEvent> event_data;
};

now as soon as I assign AEvent to sharedPointer to BaseEvent I loose
the event type and I have to use static cast to actually get back the
AEvent.

and I don't see how deferred_event would fit together with other rows
which are using AEvent of BEvent ?

 I think he only think it would solve is avoiding the copy of
even_data during event queuing. And gives us problems with deletion if
the object is created by a factory and removed by a recycle. because
you can create  the shared pointer like this :
boost::shared_ptr<AEvent> mySPtrAEvent(myFactory::factory<AEvent>());
when there is a static factory method exist and returning a pointer to
the AEvent  for event creation. but how you call instead of delete
whit shared pointers something like myFactory::recycle(pAEevent) ?

thanks for your help !!!.
Br.
Richie
...
This would solve both issues as you would have a single event to be
deferred, and it would be copyable but would still retain polymorphic
data needed to process event.
HTH
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