IsMissing Function Example

This example uses the IsMissing function to check if an optional argument has been passed to a user-defined procedure. Note that Optional arguments can now have default values and types other than Variant.

Dim ReturnValue
' The following statements call the user-defined function procedure.
ReturnValue = ReturnTwice()   ' Returns Null.
ReturnValue = ReturnTwice(2)   ' Returns 4.

' Function procedure definition.
Function ReturnTwice(Optional A)
   If IsMissing(A) Then
      ' If argument is missing, return a Null.
      ReturnTwice = Null
   Else
      ' If argument is present, return twice the value.
      ReturnTwice = A * 2
   End If
End Function