Re: How does libsigc++ accept member functions?

[Chris Vine <chris cvine freeserve co uk>]

On Fri, 05 Jun 2009 08:51:38 +0400
Igor Gorbounov <igorbounov topazelectro ru> wrote:

> Daniel Elstner пишет:
> > Am Donnerstag, den 04.06.2009, 16:01 +0400 schrieb Igor Gorbounov:
> > [...]
> >
> > As an example, I'm calling a method directly through a PMF here:
> > http://github.com/danielkitta/kcio/blob/8edc530dbfe3d998c682da0218263d7c577f5c46/kc-keyboard/controller.cc#L162
> >
> >   
> 
> Thanks, Daniel, it was helpfull, though it seems to be impossible to 
> transfer this
> pointer to some outward object, knowing nothing about the class with 
> member function.

Yes, but you can pass an opaque callback object to an outward object.
The callback object which would comprise just a functor with an
operator()() method containing:

a) a pointer or reference to the particular object on which you want to
invoke a method;
b) a pointer to member function referencing the particular member
function that you want to invoke;
c) any arguments that you want to pass to the function call.

Such an object is sometimes called a closure and is entirely opaque and
self-contained.  The outward object does not need to know what is in
the closure, all it needs to do is call operator()() and whatever
happens to be in the closure will execute.

If in addition you have a template function to instantiate the
callback objects, which (as it would be a template function) can use
automatic type deduction, such callback objects become trivial to
create and use.

I have such a callback functor class which I sometimes use in preference
to sigc::slot/sigc::mem_fun which I can e-mail you if you like.

Chris