[Development] Circular dependencies for Q_PROPERTY

Mike Krus mike.krus at kdab.com
Mon Apr 27 11:52:04 CEST 2020


I have 2 classes, A and B, derived from QObject, each have a property
of type pointer-to-other-class. So

class A : public QObject {
Q_PROPERTY(B *foo …)


class B : public QObject {
Q_PROPERTY(A *foo …)

Because of the circular dependency, I can’t #include the full class
definition, just do forward declaration.

Now this fails in Qt 6, seems the moc generated code needs the 
full class declaration.

Looking at generated moc code, looks like creating the meta object
requires a qt_metaTypeArray<A*, bool> which checks that A derives
from QObject by calling  IsPointerToTypeDerivedFromQObject
which uses sizeof() which requires the full type.

Any way around this? Seems like a rather big regression compared
to Qt 5…


Mike Krus | mike.krus at kdab.com | Senior Software Engineer
KDAB (UK) Ltd., a KDAB Group company
Tel: UK Office +44 1625 809908   Mobile +44 7833 491941
KDAB - The Qt Experts, C++, OpenGL Experts

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 4193 bytes
Desc: not available
URL: <http://lists.qt-project.org/pipermail/development/attachments/20200427/fb88cf07/attachment-0001.bin>

More information about the Development mailing list