QtQml needs the private just for one detail which nobody else should need it for: Tracking additional dependencies and marking the binding as dirty. Exporting the private requires hiding some variables and providing accessors, to compile with MSVC - including the removal of QVarLengthArray usage. Upside: The binding structure shrinks by 8 bytes and the encapsulation makes it a little easier to change things without breaking declarative, ... in the unlikely event ;-) Also remove setDirty() from the public API as it's not needed by QtQml and using it is dangerous, because it means that there's a risk of somebody keeping a reference (count) to the untyped binding from within the binding closure, which introduces a memory leak. Change-Id: I43bd56f4bdf218efb54fa23e2d627ad3acfafeb5 Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>