Re: [sigc] dynamic signals?

[Martin Schulze <martin-ml hippogriff de>]

Hi!

Your scenario seems to be possible to implement. You are aware, of  
course, that you loose any kind of type safety! Wrong connect/emit  
function calls would not be detected at compile time and cause the  
program to segfault at run time.

Note that

> sc.connect("second-signal", sigc::ptr_fun(foo));

cannot be implemented like this. Normally, the argument to  
signal.connect() is converted to a slot object implicitly according to  
the type the parameter to signal.connect(). This type depends on the  
template signature of the signal. Since in the code above the  
information from the signal's template signature is not available, the  
exact type of the slot has to specified manually like in:

  sc.connect("second-signal",  
sigc::slot<void,int>(sigc::ptr_fun(foo)));

Problems can also arise in your emit() function if the parameter types  
don't match the signal's template signature exactly. E.g. if you  
exchange:

> sc.emit("second-signal",2);

with

  sc.emit("second-signal",2.1);

your emit() template function will be instantiated for type "float" and  
you will cast the signal "second-signal" to signal<void,float> where  
the real type is signal<void,int>!

Regards,

  Martin

Am 01.04.2005 20:02:57 schrieb(en) Aaron Griffin:
> Hello everyone,
> I've been looking into libsigc++ briefly, and I like it alot.  I have
> one implementation question for you all.  I would like to product the
> following behavior:
>
> /***************************************************/
> void foo(int i)
> {
>    std::cout << "called with i="
>              << i << std::endl;
> }
>
> signal_creator sc;
> sc.create("first-signal",sigc::signal<void>());
> sc.create("second-signal",sigc::signal<void,int>());
>
> sc.connect("first-signal", sigc::bind(foo,1));
> sc.connect("second-signal", sigc::ptr_fun(foo));
>
> sc.emit("first-signal");
> sc.emit("second-signal",2);
> /***************************************************/
>
> is this possible? my idea was to create a private
> std::map<std::string,sigc::signal_base> and insert upon creation.  I
> think I may have difficulty when creating both the connect and emit
> signatures...
>
> I would assume the "connect" method would be typed with a
> "sigc::slot_base" - but I'm curious as to what would happen if a slot
> expecting 3 parameters is attached to a signal emitting 1
> parameter...
>
> as for the emit signature, I was planning on just overloading it to
> take 0 to 7 parameters, and up-cast the signal accordingly before
> calling emit
>
> would this work? is there a better way to do it?
>
> Thanks for your time,
> Aaron Griffin
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