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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