Qt: meaning of slot return value?


Question

According to the documentation the return value from a slot doesn't mean anything.
Yet in the generated moc code I see that if a slot returns a value this value is used for something. Any idea what does it do?


Here's an example of what I'm talking about. this is taken from code generated by moc. 'message' is a slot that doesn't return anything and 'selectPart' is declared as returning int.

case 7: message((*reinterpret_cast< const QString(*)>(_a[1])),(*reinterpret_cast< int(*)>(_a[2]))); break;
case 8: { int _r = selectPart((*reinterpret_cast< AppObject*(*)>(_a[1])),(*reinterpret_cast< int(*)>(_a[2])));
    if (_a[0]) *reinterpret_cast< int*>(_a[0]) = _r; }  break;
1
25
1/7/2011 12:35:59 PM

The return value is only useful if you want to call the slot as a normal member function:

class MyClass : public QObject {
    Q_OBJECT
public:
    MyClass(QObject* parent);
    void Something();
public Q_SLOTS:
    int Other();
};

void MyClass::Something() { int res = this->Other(); ... }

Edit: It seems that's not the only way the return value can be used, the QMetaObject::invokeMethod method can be used to call a slot and get a return value. Although it seems like it's a bit more complicated to do.

14
9/30/2008 5:25:34 PM

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