[Development] unique_ptr and Qt, Take 2

[Konstantin Ritt]

Ivan,

note that observer_ptr is mostly like

template<typename T>using observer_ptr = T*;


so what about


layout2->addWidget(layout->addWidget(make_unique<QPushButton>("right")))->setFlat(true);

?


Regards,
Konstantin


пт, 3 мая 2019 г., 21:41 Иван Комиссаров <abbapoh at gmail.com>:

> Thiago, can you please elaborate how you see this?
>
> For a simple TreeItem a pair of std::unique_ptr/std::observer_ptr should
> be enough (with a bunch of convenience methods to insert children):
>
> struct TreeItem
> {
>    observer_ptr<TreeItem> parent;
>    vector<unique_ptr<TreeItem>> children;
> };
>
> Yes, the code becomes a bit verbose, but the ownership transfer is now
> visible with those (ugly) std::moves.
>
> I can think of an alternative of using shared pointers (since we already
> have a QPointer aka WeakPointer<QObject>) but I think it gives too much
> overhead just to support corner cases.
>
> If QLayout::addWidget() will return an observer_ptr*, you can just do
>
> auto button = layout->addWidget(make_unique<QPushButton>(«RIGHT»));
> button->setFlat(true);
>
> * ok, you need a template version of addWidget for that, but since c++ is
> all about templates these days it doesn’t really a disadvantage
>
>
> > 3 мая 2019 г., в 20:24, Thiago Macieira <thiago.macieira at intel.com>
> написал(а):
> >
> > On Friday, 3 May 2019 10:22:20 PDT Daniel Teske wrote:
> >> std::unique_ptr<QPushButton> rightButton =
> >> std::make_unique<QPushButton>("RIGHT");
> >> layout->addWidget(std::move(rightButton));
> >
> > The problem in this particular example is that once you've added the
> widget,
> > the rightButton smart pointer no longer has a pointer. You can't
> continue to
> > set up your push button. In most cases, this is just a matter of moving
> the
> > set up before the addition / reparenting, or using the other idiom where
> the
> > object is never in a smart pointer in the first place.
> >
> > So this begs the question of whether std::unique_ptr is the best smart
> pointer
> > for this scenario. Would it make sense to create one that understands
> parent-
> > child relationship?
> >
> > --
> > Thiago Macieira - thiago.macieira (AT) intel.com
> >  Software Architect - Intel System Software Products
> >
> >
> >
> > _______________________________________________
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> > Development at qt-project.org
> > https://lists.qt-project.org/listinfo/development
>
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