[Development] qMoveToConst helper for rvalue references to movable Qt containers?

[Elvis Stansvik]

(Adding back the mailing list)

Den lör 20 okt. 2018 kl 23:54 skrev Elvis Stansvik <elvstone at gmail.com>:
>
> Den lör 20 okt. 2018 kl 23:50 skrev Giuseppe D'Angelo
> <giuseppe.dangelo at kdab.com>:
> >
> > Il 20/10/18 19:37, Elvis Stansvik ha scritto:
> > > If the C++ wizards considered this but were hesitant, then I think
> > > it's right that Qt is hesitant as well. I hadn't really considered
> > > potential life-time issues, so I guess what we're doing might possibly
> > > be unsafe (?).
> >
> > Probably in the sense that the function you pasted can be applied like this:
> >
> > QVector<Obj> v;
> > for (auto &o : qMoveAsConst(v)) ~~~; // compiles with an lvalue!
> > use(v); // unspecified behavior
>
> Ah yes, it may be that the standards folks simply didn't want this
> because of foot-shooting potential like this.

Another potential foot-shooter I found on an SO question
(https://stackoverflow.com/a/39051612/252857):

for (auto const &&value : as_const(getQString()))  // whoops!
{
}

Elvis

>
> >
> >
> > > What's GCE? Some optimization? (Google "c++ gce" didn't give me anything).
> >
> > Guaranteed Copy Elision:
> >
> > > https://en.cppreference.com/w/cpp/language/copy_elision
>
> Thanks!
>
> Elvis
>
> >
> > My 2 c,
> >
> > --
> > Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
> > KDAB (France) S.A.S., a KDAB Group company
> > Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
> > KDAB - The Qt, C++ and OpenGL Experts
> >