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varUnknown

varUnknown = 13

Example​

function IsUnknownInterface(const Value: Variant): Boolean;
begin
  Result := (VarType(Value) and varTypeMask) = varUnknown;
end;

Usage​

varUnknown identifies a reference-counted IUnknown or IInterface Variant without guaranteeing late-bound Automation dispatch.

Additional Technical Info​

varUnknown is the base TVarType code $000D for an IUnknown/Delphi IInterface pointer. The Variant normally owns a reference-counted interface but does not promise IDispatch late binding.

Use varDispatch for an Automation-dispatch representation. An IUnknown may support IDispatch or another requested interface through QueryInterface, but that capability must be checked; the type tag alone cannot establish it.

Ownership and safety

  • Copying/assigning an owned value normally increments the interface reference count; clearing releases it and may destroy the underlying object.
  • A varByRef combination borrows an external interface slot and depends on its lifetime.
  • A nil pointer can still have an interface tag. Handle nil and unsupported-interface outcomes.
  • Interface calls can execute native/external code with arbitrary I/O, latency, re-entrancy and exceptions. Respect COM apartment/thread rules and never assume thread safety from the tag.

VarType reads only the type field and does not call the interface. Converting to a dispatch or concrete interface may query the object and fail.

The example is source-reviewed only; no interface reference was acquired or released.

External references

Created 2026-07-15