[Development] QMetaType support for QFuture

[Sona Kurazyan]

I see the problem.
I guess adding an internal API in QtCore (likely in QtPrivate namespace), which is a friend to QFuture and gives access to its d-ptr is the only option then. At least I cannot think of a better way.

Best regards,
Sona

> -----Original Message-----
> From: Arno Rehn <a.rehn at menlosystems.com>
> Sent: Friday, May 7, 2021 6:28 PM
> To: Sona Kurazyan <sona.kurazyan at qt.io>; Qt development mailing list
> <development at qt-project.org>
> Subject: Re: [Development] QMetaType support for QFuture
> 
> 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
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