DISPIDNEWENUM

DISPID_NEWENUM, sometimes written as DISPID_NEWENUM or DISPIDNEWENUM, is the dispatch identifier used in COM automation to access the _NewEnum member of a collection object. The value is defined as -4 in the standard OLE Automation headers. When a client uses IDispatch to interact with a collection, it maps the string "_NewEnum" to this dispatch ID and invokes it with a property get request to obtain an enumerator, typically an IEnumVARIANT.

The obtained enumerator provides the items of the collection one by one, as VARIANT values, enabling language environments that host COM objects to implement foreach or For Each looping constructs. Languages such as VBScript, JScript, and other automation-enabled environments rely on this convention to iterate over collections.

What distinguishes DISPID_NEWENUM is its role as a standardized hook for enumeration rather than a regular property. Not all COM objects expose _NewEnum; only those designed to be enumerable implement this member, making the presence of DISPID_NEWENUM a compatibility feature for scripting and automation clients.

In practice, developers rarely call DISPID_NEWENUM directly; instead, they rely on the language runtime's automation layer to access the enumeration interface. Understanding this dispatch ID helps explain how iteration over COM collections is implemented across diverse hosts and languages.

See also: IDispatch, IEnumVARIANT, VARIANT, DISPID_PROPERTYPUT.