Public Interface IArray
  Function Count() As Integer
End Interface

Public Interface ICounter
  Function Count() As Integer
End Interface

Public Interface ICountArray
  Inherits IArray
  Inherits ICounter
End Interface

Module CountArrayTest
  Sub Test(ByVal x As ICountArray)
    Dim nCount = CType(x, ICounter).Count()
    Dim nArrayCount = CType(x, IArray).Count()

    'Other code..
  End Sub
End Module