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Most classes in Qt have a default constructor. Many classes take a QObject* or QWidget* as constructor argument with default value nullptr. The class QAction also has such a constructor taking a QObject* as argument, but there is no default value. Therefore, QAction is not default constructable. Why is that? Does a QAction really need to have a parent? Or is there anything else different in QAction that explains this inconsistency?

Ralph Tandetzky
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    It has a default value now in [Qt 5.7](https://code.qt.io/cgit/qt/qtbase.git/tree/src/widgets/kernel/qaction.h?h=5.7#n93). However, it did not have a default value in [Qt 5.6](https://code.qt.io/cgit/qt/qtbase.git/tree/src/widgets/kernel/qaction.h?h=5.6.2#n87). – Mike Oct 11 '16 at 08:43
  • @Mike Good catch. I'm working with Qt 5.5 and did not know of the change. This explains it. Thanks. – Ralph Tandetzky Oct 11 '16 at 09:34
  • I'm just guessing here, but there could be a reason it was done like this originally. `QWidget::addAction(QAction*)` does not take ownership of the `QAction` object, so maybe this was a way to prevent memory leaks. – thuga Oct 11 '16 at 10:01

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Just a guess here but I would say there is no reason behind it.

In Qt 4.8 the signature is (as you mentioned) without default value for parent.

QAction(QObject * parent)

see http://doc.qt.io/qt-4.8/qaction.html

This changes in Qt 5.7 though 

QAction(QObject *parent = nullptr)

see http://doc.qt.io/qt-5/qaction.html

So I assume it was an accidental inconsistency which finally got fixed with Qt 5.7.

Kuba hasn't forgotten Monica
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Hayt
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