[Qt-interest] void value not ignored as it ought to be

[Rohan McGovern]

On Friday 27 March 2009, ext Andrea Franceschini wrote:
> 2009/3/26, Thiago Macieira <thiago.macieira at trolltech.com>:
> > Does the Doodle::PadWidget class have a Q_OBJECT macro?
>
> Nope. Adding it seems to have fixed the problem. I thought that a
> class could safely inherit the expansion of Q_OBJECT but it seems
> I'm wrong. Probably I'm missing something about the Moc, right?

If you have a class Widget which has Q_OBJECT, and a subclass 
PadWidget which does not have Q_OBJECT, then PadWidget has the same 
metaobject as Widget.  In other words, the metatype system sees all 
PadWidget instances as Widgets.

In some situations that's appropriate, so one could say a class 
can "safely inherit the expansion of Q_OBJECT".  However as you 
discovered, qobject_cast requires the target class to have its own 
unique metaobject.

-- 
Rohan McGovern
Qt Software, Nokia