[Development] QMetaType support for QFuture

Konstantin Ritt ritt.ks at gmail.com
Sat May 8 02:29:24 CEST 2021

I was implementing a similar feature few years ago and had the same problem
with QFuture internals --
As there was no interest in making those better, I had to hack it in a way
I won't promote here ;p
But since QFuture took a new life with QPromise, it becomes even more
useful than before and deserves some improvements IMO.
Maybe we could add a public accessor to future's d via
QFutureInterfaceBase? Will that be acceptable?


пт, 7 мая 2021 г. в 19:28, Arno Rehn <a.rehn at menlosystems.com>:

> Hi Sona,
> On 07.05.21 17:11, Sona Kurazyan wrote:
> > You could use the QFutureInterfaceBase (non-templated) class directly
> > to build a type-erased future, that's basically what QFuture is using
> > underneath. Although it's internal (not documented and is considered
> > to be private), but it's declared in a public header
> > (qfutureinterface.h) and you can still use it. QFutureInterfaceBase's
> > methods for accessing its internals are public (with a few exceptions
> > that you probably won't need to use). I hope that helps.
> Yep, that's what I thought as well. But I cannot get it from an existing
> QFuture because it's a private member. We could add some private API to
> extract the QFutureInterfaceBase, however.
> Anyway, I think I'll have to add some QMetaType magic anyway for this to
> work. In QtWebChannel, we get the method return value wrapped in a
> QVariant, so the QFuture<T> is wrapped in a QVariant. From there, I
> cannot extract the QFutureInterfaceBase in any way.
> I *could* just memcpy from QVariant's data pointer to a
> QFutureInterfaceBase*, but I'm pretty sure that this is UB.
> Any pointer where to start?
> Regards,
> Arno
> --
> Arno Rehn
> Tel +49 89 189 166 0
> Fax +49 89 189 166 111
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