Qt 4.6 behaves differently when "overloading" signals

[Dario Freddi]

On Saturday 07 November 2009 19:19:22 Thiago Macieira wrote:
> Em Sábado 7. Novembro 2009, às 18.26.48, Dario Freddi escreveu:
> > On Saturday 07 November 2009 18:19:44 you wrote:
> > > That warning and behaviour is about 5 or six years old. I asked thiago
> > >  about it some weeks before. You only see it now because it only
> > > appears in qt developer builds which we only started to use when
> > > switching to the qt git repo.
> > >
> > > So i think the ... it worked with qt <4.6 may be unlikely. Are you
> > > really sure?
> >
> > Sure, otherwise for example the k3bsetup and some other polkit-qt
> >  applications wouldn't work as expected with qt 4.5.
> 
> The warning is correct.
> 
> Overriding signals is an extremely bad idea. Since signals aren't virtual,
>  the code in the base class that emits the signal will emit the lower-ID
>  signal. However, the connect() call searches from the most derived class
>  towards QObject -- that means you connect to the most-derived class's
>  signal.
> 
> In other words, the signal is emitted, but it's never caught.
> 
> DO NOT override signals.

Could be good to have this information somewhere. But being good or bad, the 
problem is that some applications working with Qt 4.5 won't work with Qt 4.6 
(even if I still would like to test using a non developer build, if somebody 
could point me in the right direction).

I can come up with a patch for partitionmanager and that wouldn't hurt since 
it's an application, whereas polkit-qt is a library and quite a more complex 
matter, since I would have to add another (different) signal or work around it 
somehow, and to avoid having people rewrite parts of their application I'd 
surely favor for the second, which would anyway bring up problems.

> 
> Also, Michael is right: that warning is extremely old. It was added for Qt
> 4.0.

The problem is that is showing (at least for me) only using 4.6, but could be 
because of developer builds 

> 

-- 
-------------------

Dario Freddi
KDE Developer
GPG Key Signature: 511A9A3B
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