[Interest] Are slots even needed these days?

[Nye]

On Fri, May 13, 2016 at 2:43 PM, d3fault <d3faultdotxbe at gmail.com> wrote:


> It's to work around the diamond inheritance problem, so yea admittedly
> it's ugly. Know a cleaner way? I'm all ears.
>

Declare your signals directly into the classes that provide them and
connect compatible methods, that'd be the cleaner way. But, yes, I admit,
it doesn't work with an abstract class like you want.


> They can be pure virtual in the interface, just don't mark them virtual in
> the derived classes and you won't get that warning.
>

I would assume this warning was put there for a reason by the Qt devs,
wouldn't you?


> If they're both reinterpret_casts then it compiles but segfaults.
>

Of course it segfaults, these aren't POD structures, they have pointers to
the virtual tables, you can't just reinterpret_cast from one type to the
other. That's why dynamic_cast was invented in the first place. If you
properly cast to QObject * (that is with dynamic_cast) the result is like
from the previous connect: "QObject::connect: signal not found in A"


> Please download the attachment and test out your connect statements (both
> compilation and execution) before responding with another attempt.
>

I had duly noted that the snippet I provided wan't tested, so there's no
need to get overly excited.

 RTTI has overhead, and while you're right that "forcing the interface to
> know about implementation details of derived classes" is usually a bad
> idea, in this case the goal is to make a "signals & slots interface", so
> it's guaranteed that all derived classes will ultimately inherit QObject.
>

It does, but so does the moc generated data. It's how qobject_cast works
without RTTI in the first place, it basically does what RTTI does, and even
some more.

As a side note, I remembered how you can cast to the interface without the
need of RTTI:
Declare the interface with Q_DECLARE_INTERFACE and list in the Q_INTERFACES
macro the interfaces you implement. Then you can do qobject_cast<Interface
*>(a); (where a is QObject *).
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