This (header-only) library can be used to create an application using Qt, without the need of the moc (MetaObject Compiler). It uses a different set of macro than Qt and templated constexpr code to generate the QMetaObject at compile-time. It is entirely binary compatible with Qt.
Blog post presenting the project: https://woboq.com/blog/verdigris-qt-without-moc.html (2016)
Blog post with some implementation details: https://woboq.com/blog/verdigris-implementation-tricks.html (2018)
Github Actions:
For an introduction, see the feature/main.cpp. See also a more detailed documetation of the macros in the source code.
For the advanced generic C++ API see the app_api/main.cpp
For the experimantal QML_ELEMENT support, see qml_element folder.
Almost all features of Qt are working. The Qt test have been ported.
Features that are not yet working:
- Q_PLUGIN_METADATA: This would require compiling to the Qt's binary json. Out of scope for now.
- BINDABLE: Needs to be backported to the current C++ and Qt requirements.
- QMetaMethod::tag(): Not yet implemented, could be supported if needed, but is not really needed for anything. (not even tested by Qt's auto test)
- Q_ENUM: Working, but requires to repeat the name of every enum value. Could be improved.
New features compared to Qt with moc:
- Compile QObjects in single C++ compiler run.
- Support for templated QObject.
- Support for QObject nested in another class.
Some Quirks:
- QML_ELEMENT: This is a Qt6 feature that automatically registers the QObjects for QML. Works by storing JSON in extra data segment that is dropped during linking. Only works on Posix, Mac or Windows targets. Requires CMake or Patched (Obj support) Qbs to work.
The library consist of only two headers files. You can either copy these header files in your
project, or adjust the include paths so that the compiler finds them.
You will find the headers in the 'src/' sub-directory.
Also make sure to set your compiler in, at least, C++20 mode. With qmake, you can do that with
CONFIG += c++20.
Tested with Qt >= 6.2. Need a compiler that can do C++20 properly, such as GCC 12+ or Clang 13+, or MSVC 2019+.
When running lupdate, add the argument -tr-function-alias Q_DECLARE_TR_FUNCTIONS+=W_OBJECT to
avoid the warning that your class are not using the Q_OBJECT macro.
This table show the correspondence between Qt macro and Verdigris macro:
| Qt macro | Use the Verdigris macro instead |
|---|---|
Q_OBJECT |
W_OBJECT(MyClass) ... W_OBJECT_IMPL(MyClass) |
public slots: void mySlot(int x); |
void mySlot(int x); W_SLOT(mySlot) |
signals: void mySignal(int x); |
void mySignal(int x) W_SIGNAL(mySignal,x) |
Q_PROPERTY(int myProperty WRITE setProp READ getProp NOTIFY propChanged) |
W_PROPERTY(int, myProperty WRITE setProp READ getProp NOTIFY propChanged) |
Q_GADGET |
W_GADGET(MyClass) ... W_GADGET_IMPL(MyClass) |
Q_INVOKABLE void myFunction(int foo); |
void myFunction(int foo); W_INVOKABLE(myFunction) |
Q_INVOKABLE MyClass(int foo); |
MyClass(int foo); W_CONSTRUCTOR(int) |
Q_CLASSINFO("foo", "bar") |
W_CLASSINFO("foo", "bar") |
Q_DECLARE_INTERFACE(MyInterface, "my.interface") ... Q_INTERFACE(MyInterface) |
Q_DECLARE_INTERFACE(MyInterface, "my.interface") ... W_INTERFACE(MyInterface) |
Q_NAMESPACE |
W_NAMESPACE(MyNs) ... W_NAMESPACE_IMPL(MyNs) |
| Q_ENUM/Q_FLAG/Q_ENUM_NS/Q_FLAG_NS | W_ENUM/W_FLAG/W_ENUM_NS/W_FLAG_NS |
The macros were inspired by CopperSpice. The template code was based on previous work: https://woboq.com/blog/reflection-in-cpp-and-qt-moc.html
Differences with CopperSpice:
- Contrary to CopperSpice, this is not a fork of Qt, but just an alternative set of macro to define Qt objects and signals and slot in a way that is binary compatible with Qt, but does not require moc. This is to be used with the normal Qt. CopperSpice being an entire fork of Qt, it has more differences with Qt and is not kept up to date with all the new features coming in Qt.
- The QMetaObject is built at compile time in the read only section (like what moc does). CopperSpice builds it at run-time when the library is loaded. So CopperSpice takes more memory and load slower.
- With CopperSpice, you cannot declare your slot within the class definition.
- CopperSpice uses
__LINE__in its macro making it impossible to declare several things in one line or to declare objects or properties from macros. - The usability of some macro was (in our opinion) improved.
- The additional Q_OBJECT_IMPL
Like Qt, this library is under the dual licence LGPLv3 and GPLv2. Being header-only, this removes many of the obligations of the LGPLv3.
If you have any questions or remark please email info@woboq.com