[Development] RFC: Improved Q_ENUM

[Olivier Goffart]

Hi,

The support in moc was already merged, but I am still waiting for reviews.
Mainly:

https://codereview.qt-project.org/103529
QMetatype: Register the QMetaObject of a Q_ENUM or Q_FLAG

https://codereview.qt-project.org/91865 Introduces QMetaEnum::fromType

https://codereview.qt-project.org/89416/
Add a qDebug operator overload to handle registered enum
(I know it does not work yet for QFlags, but that can come later)

https://codereview.qt-project.org/91862 
Use Q_ENUM and Q_FLAG in the Qt namespace
(needed for the test of the first patch)

-- 
Olivier 

Woboq - Qt services and support - http://woboq.com - http://code.woboq.org


On Monday 15 December 2014 14:38:00 Olivier Goffart wrote:
> Hello,
> 
> I have been working on some improvements to moc and the meta type system to
> improve Q_ENUM. Those changes are targeting Qt 5.5
> 
> You can see the list of change there in the q_gadget topic (I put the
> changes in that topic even if it is an orthogonal changes to the Q_GADGET
> changes that are already in)
> 
> https://codereview.qt-project.org/#/q/status:open+project:qt/qtbase+branch:d
> ev+topic:q_gadget,n,z
> 
> This is something that I have actually started working on a long time ago.
> The problem I wanted to solve was to show the actual string of the value
> when using qDebug with enum values that are registered with Q_ENUMS
> I tried many different option, and finally got a working solution, but it
> does require small changes, so I added a new macro Q_ENUM to keep
> compatibility
> 
> Q_ENUM is almost the same as Q_ENUMS, but:
>  - It can only contains one enum at the time, while you can put several in a
> Q_ENUMS
>  - It need to be placed *after* the enum declaration in the class.
> 
> Q_ENUMS is still existing and do not regress. But if you use Q_ENUM instead,
> you get:
>  - Using it with qDebug prints the actual string of the value.
>  - It is automatically registered as a QMetaType and you do not need
>    Q_REGISTER_METATYPE anymore
>  - It is also possible to get the related QMetaObject from the QMetaType.
>  - You can get the QMetaEnum using the new QMetaEnum::fromType<T>()
>  - a QVariant containing that enum can automatically be converted to QString
> or QByteArray with the value name. Also, if the QVariant contains a QString
> or a QByteArray with a value name, it can be converted to the enum type.
> (This could be useful for QML as well, as you should not need to
> artificially expose the enums to QML anymore)
> 
> At first, I wanted to deprecate Q_ENUMS and show a warning when Q_ENUMS is
> used. But because it is a bit of work to move to Q_ENUM, I just did not put
> a warning yet.
> 
> I can already hear the resistant to change nay-sayer "I like to put my
> Q_ENUMS at the beginning of the class with all the meta-stuff".  Well,
> Q_ENUM can go directly after the enum in question, so it stays together.
> This is also where you would put things like Q_DECLARE_FLAGS
> 
> Any opinions or comments?
> 
> You can review the patches. (First patch is there:
>  https://codereview.qt-project.org/89415/ )