I can't understand the new syntax of connect

Mr Pang

The definition of connect is as below:

inline QMetaObject::Connection QObject::connect(const QObject *asender, const char *asignal,
                                            const char *amember, Qt::ConnectionType atype) const
{ return connect(asender, asignal, this, amember, atype); }

And I can't understand how it work like

connect(new QSpinBox, static_cast<void(QSpinBox::*)(int)>(&QSpinBox::valueChanged), [=](auto v){});

Why function pointer and lambda function can convert to

const char *

?

Chris Kawa

Why function pointer and lambda function can convert to const char *

Directly they can't and they don't in this example. You've got the wrong overload. Here's the list: connect overloads.

The one used here is

template<typename PointerToMemberFunction, typename Functor>
QMetaObject::Connection connect(const QObject *sender, PointerToMemberFunction signal, Functor functor)

JKSH

This post is deleted!

JKSH

@Mr-Pang said in I can't understand the new syntax of connect:

static_cast<void(QSpinBox::*)(int)>(&QSpinBox::valueChanged)

P.S. It is nicer to write

QOverload<int>::of(&QSpinBox::valueChanged) (C++11), OR
qOverload<int>(&QSpinBox::valueChanged) (C++14 and newer)

P.P.S. You might find this article helpful: https://doc.qt.io/qt-5/signalsandslots-syntaxes.html

Mr Pang

@Chris-Kawa
OK. I just use qtcreator to jump and it takes me to wrong place.

Mr Pang

@JKSH
Yes. I think doc.qt.io may update the doc about QSpinBox since my syntax is copied from there.

JKSH

@Mr-Pang said in I can't understand the new syntax of connect:

I think doc.qt.io may update the doc about QSpinBox since my syntax is copied from there.

The latest version of the documentation (Qt 5.13.1) uses QOverload: https://doc.qt.io/qt-5/qspinbox.html

Anyway, has your original question been answered? Do you understand the new connect syntax now?