Re: Connecting signals syntax.

[Marko Anastasov <marko marko anastasov name>]

On Sat, 2007-01-13 at 15:22 +0100, German Diago Gomez wrote:
>  When I want to connect some signal to a slot, I think the syntax should be
> clearer. Why have I to do:
> 
>    button.signal_clicked().connect(sigc::mem_fun(this, &MyClass::myFunc));
>    button.signal_clicked().connect(sigc::ptr_fun(&myFunc));
> 
> When I could do:
> 
>    button.signal_clicked().connect(this, &MyClass::myFunc);
>    button.signal_clicked().connect(&myFunc);

connect() expects a sigc::slot, which is what sigc::mem_fun() and
sigc::ptr_fun() provide.

> But the thing gets worse when you combine that with bind:
>  
>    button.signal_clicked().connect(boost::bind(sigc::mem_fun(this,
> &MyClass::myFunc), data));

There's sigc::bind for that matter.

> This is difficult to write. I always have to think carefully what I'm writing.
> Otherwise I make mistakes.

Well, binding is not very common when dealing with widgets' signals.
But anyway, you should always think carefully when programming :).

>   I think that sigc should be replaced by boost::function which is more powerful
> and you haven't to deal explicitly with mem_fun and ptr_fun because it has a
> better type deduction system.

They are not the same. libsigc++ implements a typesafe callback system
for standard C++ [1]. A signals and slots system. Boost equivalent is
boost.signals, actually influenced by libsigc++ [2] . However, gtkmm
won't be switching to boost.signals.

>   And I think that instead of using bind, you could overload connect to receive
> additional parameters until an arbitrary number. This would make the syntax
> like this:
> 
>   button.signal_clicked().connect(this, &MyClass::myFunc, data1, data2);
> 
>  You could do this for an arbitrary number of arguments, say, 10 arguments for
> example. I think that syntax matters because you have to deal with connections
> in code since the signaling system is type-safe and you can't do it from glade
> like in python or C.

This is possible with libsigc++. It supports arbitrary number and
provides compile time typesafe callbacks [1].

I strongly suggest you go through the gtkmm tutorial [3]. There's
a section dedicated to the usage of signals and slots [4]. There is
also a separate libsigc++ tutorial [5].

Marko

[1] http://libsigc.sourceforge.net/
[2] http://www.boost.org/doc/html/signals/s06.html#id2740156
[3] http://www.gtkmm.org/docs/gtkmm-2.4/docs/tutorial/html/index.html
[4] http://www.gtkmm.org/docs/gtkmm-2.4/docs/tutorial/html/apb.html
[5] http://libsigc.sourceforge.net/libsigc2/docs/manual/html/index.html