> On 21 Jul 2020, at 22:51, Ville Voutilainen <ville.voutilai...@gmail.com> > wrote: > > On Tue, 21 Jul 2020 at 23:48, Ville Voutilainen > <ville.voutilai...@gmail.com> wrote: >> >> On Tue, 21 Jul 2020 at 22:12, Thiago Macieira <thiago.macie...@intel.com> >> wrote: >>> >>> On Tuesday, 21 July 2020 10:40:27 PDT Ville Voutilainen wrote: >>>> A very significant goal of this exercise is achieving notational >>>> convenience. Theoretical concerns about UB >>>> in the presence of papers that apparently excise that UB shouldn't >>>> stand in the way of that goal. >>> >>> Sorry, I don't agree. We can't use something that is unimplementable. >> >> Oh, when did that change? Was qobject_cast changed not to be UB? > > See also all the memcpys that are done with types that are > polymorphic, and the ones > where we memcpy types that have user-provided copy operations. qtbase > is UB left right > and center, but it's certainly interesting that when a new thing in it > might be clarified > not to be UB after all, we perform all kinds of somersaults to avoid > such dark corners.
With the current design, notational convenience doesn’t work either: auto text = qAction->text; text.left(10); // booh ‘text’ is not a QString, but a QAction::_qt_property_api_text object, with broken... everythings. And if people can’t use auto, then you can’t use standard ranged-for to iterate over container type properties without spelling everyhing out. That’s ... not convenient, I suppose. And that problem persists, even if we expose a e.g QProperty<QStringList> reference through a public property member. The current implementation also adds, in case of us not being able to use no_unique_address, a byte or even a pointer to each class in a class hierarchy, bloating classes down in the inheritance tree. Plus the BC challenge that might come with in the long run. So, this is not only a problem of UB. There is well defined behavior that seems to get in the way. Volker _______________________________________________ Development mailing list Development@qt-project.org https://lists.qt-project.org/listinfo/development
