QT : Templated Q_OBJECT class

Question

Is it possible to have a template class, which inherit from QObject (and has Q_OBJECT macro in it\'s declaration)?

I would like to create something like adapter for

Answer 1

It is still not possible to mix templates and Q_OBJECT but depending on your use case you may use the new 'connect'-syntax. This allows at least the usage of template-slots.

Classical non-working approach:

class MySignalClass : public QObject {
  Q_OBJECT
public:

signals:
  void signal_valueChanged(int newValue);
};     


template
class MySlotClass : public QObject {
  Q_OBJECT
public slots:
  void slot_setValue(const T& newValue){ /* Do sth. */}
};

Desired usage but not compilable:

MySignalClass a;
MySlotClass b;

QObject::connect(&a, SIGNAL(signal_valueChanged(int)),
                 &b, SLOT(slot_setValue(int)));

Error: Template classes not supported by Q_OBJECT (For MySlotClass).

Solution using new the 'connect'-syntax:

// Nothing changed here
class MySignalClass : public QObject {
  Q_OBJECT
public:

signals:
  void signal_valueChanged(int newValue);
};


// Removed Q_OBJECT and slots-keyword
template
class MySlotClass : public QObject {  // Inheritance is still required
public:
  void slot_setValue(const T& newValue){ /* Do sth. */}
};

Now we can instantiate desired 'MySlotClass'-objects and connect them to appropriate signal emitters.

  MySignalClass a;
  MySlotClass b;

  connect(&a, &MySignalClass::signal_valueChanged,
          &b, &MySlotClass::slot_setValue);

Conclusion: Using template-slots is possible. Emitting template signals is not working since a compiler error will occur due to missing Q_OBJECT.