Problems with object design, how to get over ambiguous warnings.

[SPlatten]

In my original design I have created classes with are derived from Qt base widget classes and these derived classes have a common node member.

Now I am changing the design as there are elements in the node which would benefit if the node class was a base class with pure virtual functions that would be defined in the derived widget classes.

For example, originally:

    class clsQtPushBtn : public QPushButton {
    Q_OBJECT
        friend class clsXMLnode;

    private:
        clsXMLnode* mpobjNode;
    ...

Now, the new design is cleaner and more powerful:

class clsQtPushBtn : public QPushButton, clsXMLnode {
Q_OBJECT
...

The issue I'm getting now is when I try to compile I see:

moc_clsQtPushBtn.cpp:78:21: error: ambiguous conversion from derived class 'const clsQtPushBtn' to base class 'QObject':
    class clsQtPushBtn -> class QPushButton -> class QAbstractButton -> class QWidget -> class QObject
    class clsQtPushBtn -> class clsXMLnode -> class QObject
    return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
                    ^~~~~
moc_clsQtPushBtn.cpp:78:50: error: ambiguous conversion from derived class 'const clsQtPushBtn' to base class 'QObject':
    class clsQtPushBtn -> class QPushButton -> class QAbstractButton -> class QWidget -> class QObject
    class clsQtPushBtn -> class clsXMLnode -> class QObject
    return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
                                                 ^~~~~

Is there anyway to solve this?

One possible cause could be that in the original design which I haven't change yet:

class clsXMLnode : public QObject {
Q_OBJECT
....

Would removing Q_OBJECT and not deriving from QObject help?

[JonB]

@SPlatten
Start by reading through the following post in this forum: https://forum.qt.io/topic/88295/with-qt-5-6-is-it-possible-to-avoid-the-diamond-problem-when-signals-and-slots-are-defined-in-two-branches

[SPlatten]

Thanks, I think I'll have to keep the original design and look for another way to simplify things.

[kshegunov]

@SPlatten said in Problems with object design, how to get over ambiguous warnings.:

Thanks, I think I'll have to keep the original design and look for another way to simplify things.

Aggregate instead. Your button isn't a node to begin with, so here the multiple inheritance is even ideologically wrong. If you have a class Car it shouldn't inherit from SteeringWheel and Engine, the car is not an engine, nor is it a steering wheel. It has an engine on the other hand.

[SPlatten]

Your thinking depends on the granularity of the design. My design is that every thing is a node must like in OOP everything is an object.

[Christian Ehrlicher]

You simply can't derive from QObject two times - fix your design.

[SPlatten]

I was never trying to do that anyway.