[sigc] how to use signal as slot?

[Martin Bickel <martin asc-hq org>]

Hi all,

I'm currently converting an application from sigc++ 1.2 to sigc++ 2 
(tested 2.4.1 and 2.2.10).

In 1.2, I could take a signal as a slot and connect it to another signal:

SigC::Signal0<bool> signal_detected;
SigC::Signal0<bool> alarm;
signal_detected.connect( alarm );


In 2.x , it works for Signals with return type void:

sigc::signal<void> signal_detected;
sigc::signal<void> warning;
signal_detected.connect( warning ) ;


but changing the return value to bool gives a compiler error:


#include <sigc++/sigc++.h>
#include <iostream>

bool warn_people()
{
    std::cout << "There are aliens in the carpark!\n";
    return true;
}

int main()
{
    sigc::signal<bool> signal_detected;
    sigc::signal<bool> warning;

    warning.connect( sigc::ptr_fun(warn_people) );
    signal_detected.connect( warning ) ;

    signal_detected();
    return 0;
}


/home/martin/software/libsigc++-2.4.1/sigc++/functors/slot.h:103:36: 
error: void value not ignored as it ought to be
       return (typed_rep->functor_)();


Is there any way to use signals as slots without writing an adaptor 
function that emits the second signal?

Regards
Martin