Why does a functor slot must have exactly the same number of arguments as signal?

[Xeonacid]

Hi,
https://doc.qt.io/qt-5/qobject.html#connect-4 says;

A function can be connected to a given signal if the signal has at least as many argument as the slot. A functor can be connected to a signal if they have exactly the same number of arguments.

I'd like to know why. Is it just by design or a implementation issue? Any technical details?
Thanks in advance.

[J.Hilk]

@jsulm apparently an error in the documentation

void functor(){
    qDebug() << Q_FUNC_INFO;
}

class Widget : public QWidget
{
    Q_OBJECT
    QWidget *center2;
public:
    explicit Widget(QWidget *parent = nullptr)
        : QWidget(parent), center2(new QWidget(this))
    {
        connect(this, &Widget::signalWithArgument, functor);
        auto t = new QTimer(this);
        connect(t, &QTimer::timeout, this,[=]()->void{emit signalWithArgument(1);});
        t->start(1000);
    }

signals:
    void signalWithArgument(int);
};



int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    Widget w;
    w.show();

    return a.exec();
}

#include "main.moc"

works perfectly fine

[J.Hilk]

@Xeonacid
A problem of the c++ language, really

You can't call a function that expects arguments, without arguments

[jsulm]

@J-Hilk But you can connect a signal which has more parameters than the slot.
Apparently same does not work with functors.

[J.Hilk]

@jsulm apparently an error in the documentation

void functor(){
    qDebug() << Q_FUNC_INFO;
}

class Widget : public QWidget
{
    Q_OBJECT
    QWidget *center2;
public:
    explicit Widget(QWidget *parent = nullptr)
        : QWidget(parent), center2(new QWidget(this))
    {
        connect(this, &Widget::signalWithArgument, functor);
        auto t = new QTimer(this);
        connect(t, &QTimer::timeout, this,[=]()->void{emit signalWithArgument(1);});
        t->start(1000);
    }

signals:
    void signalWithArgument(int);
};



int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    Widget w;
    w.show();

    return a.exec();
}

#include "main.moc"

works perfectly fine

[Xeonacid]

@J-Hilk Thanks! Hope it can be fixed soon.
@jsulm Same thanks!