target  : (3,0x2D) IStDargUnk
status  : emitted
from    : discovery snippet 'r2_unk_param' (minimised)

' ---- modProbe.bas
Option Explicit

Public Sub Main()
  Dim v As Variant
End Sub

Function FU() As IUnknown
End Function
Function FO() As Object
End Function
Function FC() As Collection
End Function
Sub P(x As Variant)
  Dim u As IUnknown
  Set x = FU()
  Set x = u
End Sub

target disasm lines:
  modProbe.Proc_401570 | 40157C    FD2D 0C00             IStDargUnk arg_C
