Re: [Boost-users] [Function][bind]Using function to store arbitrary class and arbitrary function

From: Hughes, James (jhughes_at_[hidden])
Date: 2007-06-15 03:42:37

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] 
> [mailto:boost-users-bounces_at_[hidden]] On Behalf Of 
> Kirit Sælensminde
> Sent: 14 June 2007 10:20
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] [Function][bind]Using function to 
> store arbitrary class and arbitrary function
> 
> Hughes, James wrote:
> > Hello all,
> > 
> > I have a quick question that I hope some of the experts on 
> Function and Bind can answer. I'll give a quick précis of 
> what I would like to do.
> > 
> > We have an event system in our code. I would like to set 
> this up so that any particular event can be 'attached' to 
> arbitrary classes and functions in those classes. For 
> example, a "Print" Event may need to call an arbitrary 
> function in an arbitrary class (or a number of these). 
> Therefore the event server needs to have a list of all these 
> class/function pairs for each event type.
> > 
> > I am pretty sure I can achieve that with a combination of 
> boost::function and boost::bind. I see how I can use function 
> if I know what the class type is..I would need to store the 
> function and a this pointer in to the event server, but the 
> this pointer would need to be to a specific type - that 
> specified in the boost::function defn. Is there any way to 
> make the this pointer of an arbitrary type such that the 
> function call can be made to any arbitrary function in any 
> arbitrary class?
> > 
> > Sorry, I don't have a code snippet to help explain - that's 
> what I'm trying to figure out!!
> > 
> > There may well be better ways of doing what we need - those 
> thoughts 
> > also gratefully received (nb. Working in a multithreaded 
> environment, 
> > so boost:signals may not be appropriate)
> 
> Sounds like you're labouring under a misunderstanding of how 
> the whole function type works. The this pointer will be bound 
> into the lambda created by the boost::bind function (I always 
> use boost::lambda::bind as I don't really understand the 
> difference between them and I always think of this stuff in 
> terms of lambdas).
>

More of a complete lack of knowledge than a misunderstanding!!!

 
> Say that the event comprises of a couple of parameters sent 
> to a function. We can use something like a mouse click as an example:
> 
> string do_click( int x, int y );
> 
> The event dispatcher is going to do this sort of thing:
> 
> result = do_click( theX, theY );
> 
> A boost function that looks like that will be this:
> 
> boost::function< string ( int, int ) > event_handler;
> 
> We can tie the global function into it like this:
> 
> event_handler = boost::function< string ( int, int ) >( do_click );
> 
> So far so good. But what if the do_click is a member of a 
> mouse object? 
> You might have something like this:
> 
> Mouse mouse;
> event_handler = boost::lambda::bind( &Mouse::do_click, mouse, 
> boost::lambda::_1, boost::lambda::_2 );
> 
> (There is a complication to do with the lifetime of mouse 
> here that I'm ignoring, but you won't be able to. I tend to 
> bind a boost::shared_ptr if needed.)
> 

That what I needed. Thanks.

<snip>

James

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