[haiku-development] Re: R1/a4 initial planning

  • From: Pete Goodeve <pete.goodeve@xxxxxxxxxxxx>
  • To: haiku-development@xxxxxxxxxxxxx
  • Date: Sun, 26 Feb 2012 14:25:47 -0800

On Sun, Feb 26, 2012 at 02:37:08PM -0500, Ryan Leavengood wrote:
> I would like to see if it is possible to implement some of the nice
> parts of signals and slots without requiring a special pre-processor
> like moc. Maybe some aspects of C++0x could be used for this, such as
> lambdas. This could be an area where Haiku could innovate because of
> our ability or desire to not worry about backwards compatibility in
> R2.

Just fTR, while trying to learn something about Qt myself (never used it),
I came across the "sigslot library": http://sigslot.sourceforge.net/
(She calls it a 'library' but it's actually simply a header file with lotsnlotsa
templates.)  It's not quite the same as the Qt concept, because there's
no inter-thread invocation of slots -- they're always executed in the
calling thread -- but it might be interesting to take a look at.

As this shows, a moc isn't necessary for the concept itself, and I can't
see any fundamental reason why behind-the-scenes queueing couldn't
be added (though it would need more than a header).

I was able to whip up a quickie test program, appended below, that
wored a treat first time [once I'd read the docs properly... (:-/)].

        -- Pete --


// Test of sigslot

#include <Application.h>
#include <Window.h>
#include <Button.h>
#include <Message.h>

#include "sigslot.h"
using namespace sigslot;

class SSWindow : public BWindow {
        BButton *btn;
        SSWindow() : BWindow(BRect(40,40, 140, 80), "Test", B_TITLED_WINDOW, 0)
                btn = new BButton(BRect(10, 10, 60, 30), "Test", "TEST",
                                new BMessage('butn'));
        signal0<> click;        // A signal with no arguments
        void MessageReceived(BMessage *msg) {
                switch(msg->what) {
                 case 'butn':
                        click();// emit the signal
        bool QuitRequested()
                return true;

class SSApp : public BApplication, public has_slots<> {
        SSWindow *w;
        SSApp() :  BApplication("application/x-test-sigslot") {
                w = new SSWindow();
                w->click.connect(this, &SSApp::clicked);
        void clicked() {        // The "slot" method
                printf("button clicked\n");

main() {
        new SSApp();
        delete be_app;

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