[sigc] A std::vector of signals

[cheshirekow <cheshirekow gmail com>]

I just spent a few hours debugging an interesting case. I figured that I
would be able to declare a std::vector of independent signals, which
does not seem to be the case. Here is a minimal example:

-----begin code------
#include <iostream>
#include <vector>
#include <sigc++/sigc++.h>


void printInt(int val)
{
    std::cout << val << std::endl;
}


int main()
{
    std::vector< sigc::signal<void> > sigVec(2);
    sigVec[0].connect( sigc::bind( sigc::ptr_fun( printInt ), 0 ) );
    sigVec[1].connect( sigc::bind( sigc::ptr_fun( printInt ), 1 ) );

    sigVec[0].emit();
    sigVec[1].emit();

    return 0;
}
-----end code------

What I was expecting to see printed to the console was:
0
1

But what I got was: 
0
1
0
1

So, I guess I didn't realize that a sigc::signal object was a kind of
reference, and that:

sigc::signal<void> sigA;
sigc::signal<void> sigB = sigA;

actually only creates one signal with two names. The documentation on
http://www.cplusplus.com/reference/stl/vector/vector/ says that the
"Repetative sequence constructor" initializes the vector with "n copies"
of the same value, so no surprises there... just that I wasn't expecting
assignment of a signal object to copy the actual signal.

This is neither a complaint or a request since the only problem is that
my assumption was incorrect so my expectations were not met... but I
felt the need to share this little tidbit, since searching the web and
the list didn't point out to this feature. Of course, checking back to
the documentation I found this:

"When signals are copied they share the underlying information, so you
can have a protected/private sigc::signal member and a public accessor
method." 
(http://developer.gnome.org/libsigc
++/stable/group__signal.html#_details)

So the information was there, I guess I just missed it.