Extend existing cpp class

similar to category of Object-C, it's possible to extend existing cpp class in ZFFramework:

zfclass ExistClass : zfextend ZFObject {
    ZFOBJECT_DECLARE(ExistClass, ZFObject)
    ZFMETHOD_INLINE_0(void, funcInExistClass) {
        ZFLogTrim("funcInExistClass: %s, cast to AttachClass: %s", this, zfcast(AttachClass *, this));
    }
};
 
zfclass AttachClass : zfextend ZFObject {
    ZFOBJECT_DECLARE(AttachClass, ZFObject)
    ZFMETHOD_INLINE_0(void, funcInAttachClass) {
        ZFLogTrim("funcInAttachClass: %s, cast to ExistClass: %s", this, zfcast(ExistClass *, this));
    }
};
 
// extend ExistClass by AttachClass
ZFCLASS_EXTEND(MyRegSig, ExistClass, AttachClass)
// or
ZF_GLOBAL_INITIALIZER_INIT(MyRegSig) {
    ZFImplementDynamicRegister(ExistClass::ClassData(), AttachClass::ClassData());
}
ZF_GLOBAL_INITIALIZER_DESTROY(MyRegSig) {
    ZFImplementDynamicUnregister(ExistClass::ClassData(), AttachClass::ClassData());
}
ZF_GLOBAL_INITIALIZER_END(MyRegSig)
 
// now the ExistClass would have AttachClass's method
zfobj<ExistClass> obj;
obj->funcInExistClass();
obj->to<AttachClass *>()->funcInAttachClass();
 
// this is useful in script
ZFLuaExecute(
    "ZFImplementDynamicRegister(ExistClass.ClassData(), AttachClass.ClassData())\n"
    "\n"
    "local obj = ExistClass()\n"
    "obj:funcInExistClass()\n"
    "obj:funcInAttachClass()\n"
    );