Re: [Interest] use of deleted function errors in QList / qarraydataops.h
On 28/2/23 12:00, Hamish Moffatt via Interest wrote:
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.
Even in Qt6, it compiles with other things in the struct that aren't
assignable though, just not QVector.
struct T
{
int x = 0;
};
struct S
{
//const QVector v; // compiles if not const
const T t;
const int x = 0;
};
QVector pv;
pv.push_back({});
Hamish
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Re: [Interest] use of deleted function errors in QList / qarraydataops.h
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 ___ Interest mailing list Interest@qt-project.org https://lists.qt-project.org/listinfo/interest
Re: [Interest] use of deleted function errors in QList / qarraydataops.h
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. -- Thiago Macieira - thiago.macieira (AT) intel.com Cloud Software Architect - Intel DCAI Cloud Engineering smime.p7s Description: S/MIME cryptographic signature ___ Interest mailing list Interest@qt-project.org https://lists.qt-project.org/listinfo/interest
Re: [Interest] use of deleted function errors in QList / qarraydataops.h
On 28/2/23 11:14, Thiago Macieira wrote:
On Monday, 27 February 2023 13:05:01 PST Hamish Moffatt via Interest wrote:
On 28/2/23 04:14, Thiago Macieira wrote:
On Sunday, 26 February 2023 23:24:43 PST Hamish Moffatt via Interest wrote:
Is there a solution?
Remove the const in:
struct S
{
const QVector v; // compiles if not const
};
If S is not copyable, then QVector can't copy it and QVector requires
copying all its elements.
May I ask why that is? Qt5 QVector and std::vector are both OK with the
above.
Qt 5 QVector is not ok with the above, it just hasn't produced an error *yet*.
All Qt main containers are implicitly-shared and therefore must be able to
copy their elements. Therefore, your elements must be copyable.
std::vector doesn't have this requirement. It is copyable if the element is
copyable, otherwise it isn't.
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.
Hamish
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Re: [Interest] use of deleted function errors in QList / qarraydataops.h
On Monday, 27 February 2023 13:05:01 PST Hamish Moffatt via Interest wrote:
> On 28/2/23 04:14, Thiago Macieira wrote:
> > On Sunday, 26 February 2023 23:24:43 PST Hamish Moffatt via Interest wrote:
> >> Is there a solution?
> >
> > Remove the const in:
> > struct S
> > {
> >
> > const QVector v; // compiles if not const
> >
> > };
> >
> > If S is not copyable, then QVector can't copy it and QVector requires
> > copying all its elements.
>
> May I ask why that is? Qt5 QVector and std::vector are both OK with the
> above.
Qt 5 QVector is not ok with the above, it just hasn't produced an error *yet*.
All Qt main containers are implicitly-shared and therefore must be able to
copy their elements. Therefore, your elements must be copyable.
std::vector doesn't have this requirement. It is copyable if the element is
copyable, otherwise it isn't.
--
Thiago Macieira - thiago.macieira (AT) intel.com
Cloud Software Architect - Intel DCAI Cloud Engineering
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Re: [Interest] use of deleted function errors in QList / qarraydataops.h
On 28/2/23 04:14, Thiago Macieira wrote:
On Sunday, 26 February 2023 23:24:43 PST Hamish Moffatt via Interest wrote:
Is there a solution?
Remove the const in:
struct S
{
const QVector v; // compiles if not const
};
If S is not copyable, then QVector can't copy it and QVector requires copying
all its elements.
May I ask why that is? Qt5 QVector and std::vector are both OK with the
above.
Hamish
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Re: [Interest] use of deleted function errors in QList / qarraydataops.h
On Sunday, 26 February 2023 23:24:43 PST Hamish Moffatt via Interest wrote:
> Is there a solution?
Remove the const in:
struct S
{
const QVector v; // compiles if not const
};
If S is not copyable, then QVector can't copy it and QVector requires copying
all its elements.
--
Thiago Macieira - thiago.macieira (AT) intel.com
Cloud Software Architect - Intel DCAI Cloud Engineering
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[Interest] use of deleted function errors in QList / qarraydataops.h
I have some code which boils down to this:
#include
void test()
{
struct S
{
const QVector v; // compiles if not const
};
QVector> pv; // doesn't compile with this
//std::vector> pv; // compiles with this
pv.push_back(std::make_pair({}, {}));
}
This compiles in Qt 5.15.12, but not in 6.4.2.
The last line generates no less than 4 errors, resulting in pages and
pages of output, but essentially:
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydataops.h:472:29: error: use of deleted function
‘std::pair& std::pair::operator=(const
std::pair&)’
472 | last[i] = std::move(last[i - 1]);
| ^~~~
--
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydataops.h:475:24: error: use of deleted function
‘std::pair& std::pair::operator=(const
std::pair&)’
475 | *where = std::move(t);
| ~~~^~
--
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qcontainertools_impl.h:132:18: error: use of deleted
function ‘std::pair& std::pair::operator=(const std::pair&)’
132 | *d_first = std::move_if_noexcept(*first);
| ~^~~
--
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qcontainertools_impl.h:132:18: error: use of deleted
function ‘std::pair& std::pair::operator=(const std::pair&)’
As per the comments, it compiles if the member variable in the inner
struct is not const, or if I use a std::vector instead of QVector.
Is there a solution?
Full error text below.
Hamish
In file included from
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydatapointer.h:7,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qlist.h:8,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qvector.h:7,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/QVector:1,
from test.cc:1:
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydataops.h: In instantiation of ‘void
QtPrivate::QGenericArrayOps::Inserter::insertOne(qsizetype, T&&) [with T =
std::pair; qsizetype = long long int]’:
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydataops.h:557:37: required from ‘void
QtPrivate::QGenericArrayOps::emplace(qsizetype, Args&& ...) [with Args =
{std::pair}; T = std::pair; qsizetype = long long
int]’
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qlist.h:852:15: required from ‘T&
QList::emplaceBack(Args&& ...) [with Args = {std::pair}; T =
std::pair; QList::reference = std::pair&]’
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qlist.h:440:24: required from ‘void
QList::append(QList::rvalue_ref) [with T = std::pair;
QList::rvalue_ref = std::pair&&]’
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qlist.h:652:42: required from ‘void
QList::push_back(QList::rvalue_ref) [with T = std::pair;
QList::rvalue_ref = std::pair&&]’
test.cc:13:43: required from here
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydataops.h:472:29: error: use of deleted function
‘std::pair& std::pair::operator=(const
std::pair&)’
472 | last[i] = std::move(last[i - 1]);
| ^~~~
In file included from /usr/include/c++/10/utility:70,
from
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qglobal.h:11,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qpair.h:7,
from
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydata.h:8,
from
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydataops.h:8,
from
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydatapointer.h:7,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qlist.h:8,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qvector.h:7,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/QVector:1,
from test.cc:1:
/usr/include/c++/10/bits/stl_pair.h:211:12: note: ‘std::pair&
std::pair::operator=(const std::pair&)’ is
implicitly declared as deleted because ‘std::pair’ declares a move constructor or
move assignment operator
211 | struct pair
| ^~~~
In file included from
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydatapointer.h:7,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qlist.h:8,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qvector.h:7,
from ../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/QVector:1,
from test.cc:1:
../../dev/Qt6.4.2/6.4.2/gcc_64/include/QtCore/qarraydataops.h:475:24: error: use of deleted function
‘std::pair& std::pair::operator=(const
std::pair&)’
475 | *where = std::move(t);
| ~~~^~
In file included from
