[Development] Opinions on QTBUG-71545

Elvis Stansvik elvstone at gmail.com
Tue Nov 6 14:14:47 CET 2018

Den tis 6 nov. 2018 kl 13:56 skrev André Somers <andre at familiesomers.nl>:
> Hi,
> On 05/11/2018 20:56, Elvis Stansvik wrote:
> > Den mån 5 nov. 2018 kl 20:32 skrev Konstantin Shegunov <kshegunov at gmail.com>:
> >> Hello,
> >> Since we couldn't agree, I'd love to see some more opinions about this one.[1]
> > I may be missing some detail, but I think what Thiago says makes
> > sense. When children are destroyed, you know you're in the QObject
> > destructor (from QObject::~QObject docs: "Destroys the object,
> > deleting all its child objects."), so you know the object is now a
> > QObject, no longer a QCoreApplication. If you require your
> > QCoreApplication to be alive by the time your child object is
> > destroyed, I think you have to ensure this on your own.
> Problem is, I think, that this requirement is not always obvious. For
> your own objects, you know you cannot rely on your parent still being a
> MyClass iso of just a QObject on destruction (unless you take specific
> measures to make that so), but in this case the reliance on there still
> being a Q*Application around (not necessarily the parent) is usually not
> as obvious as a myParent->doSomethingNotFromQObject call in your
> destructor code...

Yea, very good point. I'll leave it to the grow-ups to decide what to
do with this :) It was just my first gut reaction.


> >
> > Like I said, I may be missing something, but that's what it looks like
> > to me. I can't see why there would be an exception to the object model
> > here.
> >
> > Elvis
> >
> >> Specifically:
> >> 1) Is parenting to the application object a thing?
> Yes. But you know that the same goes as for any QObject parent/child
> relationship: the parent is a QObject at the time of destruction (ok,
> with QWidget, you're in luck).
> >> 1.a) ... and should it be allowed (i.e. accepting the proposed change)?
> Yes, it should be allowed, and as you argued I think it is useful. But I
> am not sure that implies the proposed change. OTOH, as so much
> functionality in Qt requires the Q*Application to be alive (and that is
> not always obvious) , perhaps an exception *is* in order.
> >> 1.b) .. if not allowed, should we put a warning in the documentation that it is wrong and shouldn't be done at all, or at least that it's discouraged.
> >>
> >> [1] https://bugreports.qt.io/browse/QTBUG-71545
> I do think it makes sense to be able to do this, but if that is to be
> discouraged, then best be explicit about that.
> André
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