VersionIndependentProgID

VersionIndependentProgID is a concept in the Component Object Model (COM) registration that provides a version-stable alias for a COM class that may have multiple versioned ProgIDs. It allows clients to create objects without needing to specify a particular version, while the registry can map this alias to the current version in use.

In practice, a VersionIndependentProgID is a ProgID root that includes a CurVer mapping to a versioned ProgID. For example, a root like MyProduct.Component might have a CurVer value containing MyProduct.Component.2, which is the versioned ProgID. The versioned ProgID key (MyProduct.Component.2) then contains the CLSID (the class identifier) of the coclass and the actual activation details. This architecture enables applications to continue using the same ProgID even as newer versions are released; updating the CurVer value redirects activation to the newer version without changing client code.

Clients can activate COM objects by either the version-independent ProgID or the versioned ProgID. If a version-independent ProgID is registered and CurVer points to a newer version, CoCreateInstance and related calls will instantiate the updated class automatically. This mechanism supports side-by-side versioning and smoother upgrades, reducing the need for client-side updates.

Notes and best practices: VersionIndependentProgIDs are optional and must be registered consistently with their corresponding versioned ProgIDs and CLSIDs. The VersionIndependentProgID itself is not a CLSID; it is an alias that improves compatibility across multiple releases of a COM server. Examples often cited include office applications where a stable alias like Excel.Application maps to newer versioned implementations.