dispIdMember

dispIdMember is a term used in the context of Component Object Model (COM) interoperability to refer to the dispatch identifier (DISP ID) assigned to a member of a COM-visible interface that supports IDispatch. The DISP ID is a numeric value that late-bound clients use to invoke methods or access properties at runtime without compile-time knowledge of the member names.

In COM, IDispatch-based binding relies on these identifiers rather than names. During type information generation (for example, in a type library), each exposed method or property is associated with a unique DISPID. This mapping enables languages and scripting environments that use dynamic binding to call members reliably across language boundaries. The dispIdMember concept often appears in metadata, type libraries, or interop definitions to indicate the DISPID associated with a given member.

Usage and control: In environments like .NET, developers can explicitly control the dispatch ID of a member using attributes such as DispId. Specifying a DISPID helps preserve binary and cross-language compatibility, since names may be localized or changed over time. Without explicit DISP IDs, interop tooling may assign DISP IDs automatically, which can lead to instability if members are added, removed, or reordered.

Special and reserved DISPIDs: Some DISP IDs have reserved meanings for special members (for example default members or property put operations) and should be used with care to avoid conflicts or unexpected behavior in clients consuming the COM object.

See also: IDispatch, DispIdAttribute, Type Library, DISPID, TypeInfo.