>An object that implements a dual interface is not required to return the >same vptr when QIed for IDispatch that it returns when it is QIed for >its dual interface. It can, and often will because that's usually the >easiest thing to do, but it's not actually obliged to.
Indeed. QI can do whatever it needs to do; that's what it's for (to support aggregation, for example). Dual interfaces are expected (required?) to have a specific VTBL format. If IServer implements MethodX () and defines itself as dual-interface there must be 8 entries in the VTBL, the IDispatch members and MethodX(). The problem is, from a COM interface point of view, you don't know if an interface you're calling QI on is actually a dual-interface; so you can't be sure a simple cast to/from IDispatch is safe. Proxies are the prime example. =================================== This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com
