[boost] Re: Slot copying in boost::signals

From: Dirk Gerrits (dirk_at_[hidden])
Date: 2002-10-14 14:44:29

graham.shanks_at_[hidden] wrote:
> I found the following behaviour in boost::signal rather surprising
> 
>   struct EventCounter
>   {
>     EventCounter() : events(0) {}
>     void operator()() { events++; }
>     int events;
>   };
> 
>   boost::signal0<void> sig;
>   EventCounter eventCounter;
>   sig.connect(eventCounter);
>   sig();
>   std::cout << "Events: " << eventCounter.events << std::endl;
> 
> gave the output 
> 
>   Events: 0
> 
> instead of the expected 1.
> 
> On investigation the reason is that the "eventCounter" slot is copied
> and the signal emitted to the copy (presumably this is the reason why
> slot must be copy constructable).
> 
> The solution to get the expected (by me) behaviour is to use
> boost::bind, i.e.
> 
>   sig.connect(boost::bind(&EventCounter::operator(), &eventCounter));

I'd use this:

sig.connect( boost::ref(eventCounter) );

That way, a reference to your original object should get connected instead of a 
copy, so the output of your test program should be 1.

I didn't run this through a compiler so please forgive me if I made a typo or 
other mistake. ;)

Dirk Gerrits