Property Experiment

Motivation

This is a tiny experiment to see if C++ 20 can do QObject properties without moc. This experiment was inspired by André Pölnitz' e-mail¹ to the Qt Development list: "I haven't tried yet, but I have the gut feeling that one should be able to get away with..."

Well, yes: André was right. C++ 20 can almost replace moc these days:

class NObjectTest : public nproperty::Object<NObjectTest>
{
    N_OBJECT

public:
    using Object::Object;

    void modifyNotifying()
    {
        notifying = u"I have been changed per method"_qs;
    }

    N_PROPERTY(QString, constant)          = u"I am constant"_qs;
    N_PROPERTY(QString, notifying, Notify) = u"I am observing"_qs;
    N_PROPERTY(QString, writable,  Write)  = u"I am modifiable"_qs;

    N_PROPERTY_NOTIFICATION(notifying)
    N_PROPERTY_NOTIFICATION(writable)

    N_PROPERTY_SETTER(setWritable, writable)
};

The code works, and I am pretty happy with the syntax of NObject.

Important

Still this is just an experiment, a proof of concept. Many FIXMEs, lots of chances for improvement. Let me hear, what you think about it. It it worth to finish this experiment and bring it into production?

You can reach me via mathias plus github at taschenorakel in de.

The Various Experiments

More detailed documentation of the several experiments can be found in their subfolders:

The initial, but abdoned AObject Experiment can be found in the aobject folder.
A much better attempt was the MObject Experiment. It already allowed to fully define QMetaObject properties without the help of moc, but it was ugly. It can be found in the mobject folder.
The NObject Experiment in the nobject folder is my current favorite. Its usage is pretty similiar to the example above. By the number of files in this folder one could argue the experiment got out of control by now. Still I am planing to add the missing QMetaObject features beyond simple properties. Actually it seems like mechanisms behind work well enough that I could try to create a plain C++ version without any help from Qt. That would mean full QMetaObject reflection with plain C++. Wouldn't that be pretty cool?
The SObject Experiment in the sobject folder is just the plain old standard mechanism we are using with Qt for decades now.

Main Program

The main program just is a QTest fixture to verifying the implementations. It contains a few pretty nice template tricks.

Compiling, Building

You need Qt 6.5 and CMake to build. Just open CMakeLists.txt in QtCreator and give it a go. Alternatively something like this:

mkdir build && cd build
export Qt6_DIR=/path/to/your/qt6/lib/cmake/Qt6
cmake ..
cmake --build .

License

The code is offered under the terms of the MIT License.

https://lists.qt-project.org/pipermail/development/2023-December/044807.html ↩