The only way I see to write this "genericly" would be to have some virtual QVariant getValue() const and virtual QVariant setValue(QVariant v) in your base class and implement it in Derived. This way you wouldn't have to do any casting, simply b2->setValue(b1->getValue()). The implementation in Derived would do the cast to T via QVariant's value().

BTW, keep in mind that there is no such thing as "universal ref" in C++ standard. It's just a way of thinking about rvalue ref T&& in contexts which provide type deduction for T

since I hate sender() and pb->children().at(0) is even less robust I suggest (assuming you declared QMenu* MainWindow::m): connect(sel, &QPushButton::released, [=]()->void{ const QSize size = m->sizeHint(); m->popup(sel->mapToGlobal(QPoint(0,-size.height()))); }); P.S. Looking at this functionality, are you sure QToolButton is not a better choice? see QToolButton::setMenu

@VRonin said in Template: Force const parameter: why wouldn't a simple static_assert work here? It definitely would.

You're welcome ! SInce everything is OK now, please update the thread title prepending [solved] so other forum users may know a solution has been found :) Also, while browsing the forum, consider up-voting the answers that helped you, it will make them easier to find for other users :)

Hi @clogwog Use Screen to get the Screen's deimesions. Bind the width and height of root element to it.

Qt developers have investigated this before, and there is a partially-working patch. There are still a number of important challenges to work through, but devs are focussing on other things at the moment. It is not currently being actively worked on: http://comments.gmane.org/gmane.comp.lib.qt.devel/10327

Hi and welcome to devnet, That might interest you

Thanks for your answers! I think I will go with Template specialization. CU mts