Dual Interfaces

OLE Automation enables an object to expose a set of methods in two ways: via the IDispatch interface, and through direct OLE VTable binding. IDispatch is used by most tools available today, and offers support for late binding to properties and methods. VTable binding offers much higher performance because this method is called directly instead of through IDispatch::Invoke. IDispatch offers late bound support, where direct VTable binding offers a significant performance gain; both techniques are valuable and important in different scenarios. By labeling an interface as dual in the type library, an OLE Automation interface can be used either via IDispatch, or it can be bound to directly. Containers can thus choose the most appropriate technique. Support for dual interfaces is strongly recommended for both controls and containers.