IDispatchEx

IDispatchEx is a COM interface that extends the standard IDispatch interface to provide enhanced dynamic dispatch capabilities for automation objects. It is designed to support languages and hosts that expose or modify their members at run time, offering more flexible and predictable access to properties and methods than plain IDispatch alone. Objects that implement IDispatchEx can present new members on the fly, enumerate available members, and control how members are discovered and invoked.

Key capabilities include mapping member names to dispatch IDs (via GetDispID), invoking members (InvokeEx), retrieving metadata about members (GetMemberName and GetMemberProperties), and enumerating members (GetNextDispID). It also supports removing dynamic members (DeleteMemberByName and DeleteMemberByDispID). These features enable expando-style objects and more sophisticated name-based access patterns that are difficult to achieve with IDispatch alone.

IDispatchEx is optional; clients should query for the interface using QueryInterface with the IID of IDispatchEx and gracefully fall back to IDispatch if the interface is not supported. In practice, IDispatchEx is implemented by a subset of COM objects, particularly in Windows components and scripting hosts that require dynamic member management. Its use is more common in environments where dynamic languages or hosts interact with complex COM objects, rather than in general automation scenarios.