[Interest] use of deleted function errors in QList / qarraydataops.h

[Hamish Moffatt]

On 28/2/23 11:49, Thiago Macieira wrote:
> On Monday, 27 February 2023 16:22:46 PST Hamish Moffatt via Interest wrote:
>> How and when would Qt5 show an error? We have the above code working and
>> in production, and I'm able resize, copy and change, force a detach -
>> operations where QVector would need to copy elements.
> Ah, looks like it isn't going to. I expected the issue was that it didn't
> happen in this test case because it never detached. If you're definitely
> detaching, then this isn't the same issue.
>
> The issue here is that you have a type that is copy/move constructible, but
> cannot be copy/move assigned. That's usually a bad combination; the new QList/
> QVector code uses move-assignment when moving elements in the overlapping part
> of the list.
>
> We could determine that your type is not move-assignable and use a different
> strategy, but this isn't implemented right now. It might be less efficient; I
> wouldn't know.
>

Qt5's documentation (like Qt6's) does say "QVector's value type must be 
an assignable data type", so the mystery here is perhaps why our code 
works with Qt5.


Thanks,

Hamish