Pattern to register metatypes in Qt

c++, qt

Solution

I can imagine something as following:

in abstractfoobase.cpp:

namespace foo {

/// Initializer
class FooStateInit {
public:
    FooStateInit() {
        qRegisterMetaType<foo::FooState>();
    }
};
static FooStateInit fooStateInit;

} // namespace foo

Problem

Introduction I've got a library, which registers a bunch of metatypes, illustrated by this code: abstractfoobase.h ``` namespace foo { enum FooState { OK, MAYBE }; class AbstractFooBase : public QObject {...}; } Q_DECLARE_METATYPE(foo::FooState) ``` There is also a corresponding abstractfoobase.cpp, contents depending on what exactly is implemented in base class. foousingclass.h: ``` namespace foo { class FooUsingClass : public AbstractFooBase {...}; } ``` Again there is corresponding foousingclass.cpp, which has method implementations etc. Now, that `Q_DECLARE_METATYPE` enables the type for Qt template classes and `QVariant`. To enable using the type in queued signals and such, there also needs to be a corresponding call: ``` qRegisterMetaType<foo::FooState>(); ``` Question What is(are) the good place(s) to put the `qRegisterMetaType` call? I obviously don't want any expllicit initialization call from application code. The registrations must have happened after doing a `foo::FooUsingClass *f = new foo::FooUsingClass();`. In Java I'd put this kind of code in a static initialization block. I can see several ways to do this in C++ too, but none of them seem particularily nice. For example, simply putting these to `AbstractFooBase` constructor will cause the registrations being called every time a subclass instance is created, which may be undesired overhead. So those who have done this, where did you put the `qRegisterMetaType` calls?

Original source