Does Qt support virtual pure slots?

Question

My GUI project in Qt has a lot of "configuration pages" classes which all inherit directly from QWidget.

Recently, I realized that all these classes share 2 commons slots (loadSettings() and saveSettings()).

Regarding this, I have two questions:

• Does it make sense to write a intermediate base abstract class (lets name it BaseConfigurationPage) with these two slots as virtual pure methods ? (Every possible configuration page will always have these two methods, so I would say "yes")
• Before I do the heavy change in my code (if I have to) : does Qt support virtual pure slots ? Is there anything I should be aware of ?

Here is a code example describing everything:

class BaseConfigurationPage : public QWidget
{
  // Some constructor and other methods, irrelevant here.

  public slots:

    virtual void loadSettings() = 0;
    virtual void saveSettings() = 0;
};

class GeneralConfigurationPage : public BaseConfigurationPage
{
  // Some constructor and other methods, irrelevant here.

  public slots:

    void loadSettings();
    void saveSettings();
};

Answer 1

Yes, just like regular c++ pure virtual methods. The code generated by MOC does call the pure virtual slots, but that's ok since the base class can't be instantiated anyway...

Again, just like regular c++ pure virtual methods, the class cannot be instantiated until the methods are given an implementation.

One thing: in the subclass, you actuallly don't need to mark the overriden methods as slots. First, they're already implemented as slots in the base class. Second, you're just creating more work for the MOC and compiler since you're adding a (tiny) bit more code. Trivial, but whatever.

So, go for it..

Answer 2

Only slots in the BaseConfigurationPage

class BaseConfigurationPage : public QWidget
{
  // Some constructor and other methods, irrelevant here.

  public slots:

    virtual void loadSettings() = 0;
    virtual void saveSettings() = 0;
};

class GeneralConfigurationPage : public BaseConfigurationPage
{
  // Some constructor and other methods, irrelevant here.

    void loadSettings();
    void saveSettings();
};