Signals and Slot using Functor

TopNotch_Mach07

Hi ,

Can anyone explain what is going on this code. How does the Functor class acts as a Slot ?

Sorry for such a dumb question , Newbie to C++ and Qt.

class Functor {
public:
Functor(Object *object, const QString &str) :
     m_object(object), m_str(str) {}
     void operator()(int x, int y) const {
     m_object->set(x, y, m_str);
}
private:
   Object *m_object;
    QString m_str;
};
    connect(obj1, SIGNAL(coordChanged(int, int)),
    Functor("Some Text"));

Thanks.

m.sue

@TopNotch_Mach07 said in Signals and Slot using Functor:

How does the Functor class acts as a Slot ?

Hi,
it's because your connect statement connects to a function of signature (int x, int y) and the class has an operator() of the same signature.
-Michael.

VRonin

see https://wiki.qt.io/New_Signal_Slot_Syntax

New: connecting to simple function
The new syntax can even connect to functions, not just QObjects

in this case the operator() of the object is treated as a function

Andy314

Your Functor class is not a functor !
The constructor should only set parameter for the functor function. You must define a functor function in your class.

Class Functor
{
.......................
Returntype operator()(Argumentlist) { .....; return ....; }
}

Functor f(ConstructorArguments);
auto x=f(FunctorArguments); // here the syntax is like a normal function call

mrjj

Hi
If you are new to to c++
Might be good to know the what functor really means.
http://www.cprogramming.com/tutorial/functors-function-objects-in-c++.html

TLDR: Its basically just a function inside a class.
We pass the class to other class where they expect a function pointer/adress but the magic of "operator ()"
makes it work as otherwise it would complain about types.