Return a plain QMetaObject* from toDynamicMetaObject()

The only place where we use it, we swiftly cast it to QMetaObject*
anyway. Generating an object with virtual methods, only to then cast to
its non-virtual base type is dangerous. Also, if we are required to
return a QAbstractDynamicMetaObject from a method of
QDynamicMetaObjectData, we cannot implement QDynamicMetaObjectData
without also implementing QAbstractDynamicMetaObject. This indirectly
forces us to copy metaobjects around as we cannot wrap an existing
metaobject into a QDynamicMetaObjectData subclass.

Copying metaobjects around makes QMetaObject::inherits() unusable
because inherits() assumes identity is determined by identity of the
pointer.

Change-Id: Icbe697efa6fd66649eef3c91260c95cda62e3c90
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/corelib/kernel/qobject.h b/src/corelib/kernel/qobject.h
index c94fb17755..e75cf3217e 100644
--- a/src/corelib/kernel/qobject.h
+++ b/src/corelib/kernel/qobject.h
@@ -111,6 +111,9 @@ public:
     int postedEvents;
     QDynamicMetaObjectData *metaObject;
     QBindingStorage bindingStorage;
+
+    // ### Qt7: Make this return a const QMetaObject *. You should not mess with
+    //          the metaobjects of existing objects.
     QMetaObject *dynamicMetaObject() const;
 
 #ifdef QT_DEBUG