[Development] Property bindings in Qt 6

[Jason H]

> I’m all for a more declarative coding style also in C++.
> I’m wondering if we are re-inventing part of Reactive Programing a la ReactiveX with QProperty, though?
> 
> The above looks similar to (sodium-cxx):
> 
>     cell_sink<QString> surname("John");
>     cell_sink<QString> lastname("Smith”);
>     cell<QString> fullname = surname.lift(
>         lastname, [](QString s, QString l) { return s + " " + l; });
> 
>     qDebug() << fullname.sample();
>     surname.send("Emma");
>     qDebug() << fullname.sample();
> 
> or (RxJS):
> 
>     var surname = new BehaviorSubject("John");
>     var lastname = new BehaviorSubject("Smith");
>     var fullname = new BehaviorSubject();
>     r.combineLatest(surname, lastname).pipe(map(([s, l]) => { return s + " " + l; })).subscribe(fullname);
> 
>     console.log(fullname.getValue());
>     surname.next("Emma”);
>     console.log(fullname.getValue());
> 
> What is the relation of QProperty to Reactive Programing, in which ways can we orient QProperty on what is done there, or learn from insights in that field?

> Using "fullname.listen([](QString s) { qDebug() << s; });" (or "fullname.subscribe(s => console.log(s));”) instead of the explicit logging in the example above
> will print “John Smith”, whereas using change event listeners always requires special handling of the initial value.

I would (naively) think that this would be done by creating a default-constructed value, then setting it? 

So I've used knockout and observables, and at the same time used Qt, and I always preferred QML over the bindings with that framework.

I'm wondering (out loud) if we aren't kinda talking about a opposite of QGadget for our classes - one where it can just emit a changed() event for applicable setters. I'm not sure how much of moc would have to be brought in - obviously we wouldn't want it on every class...?