Elegant way to pass as an optional parameter to make the subroutine work as if it was omitted?

Question

In VB6, the function Mid(string, start, [length]) has an optional parameter length. If omitted, the whole characters after the start bound will be passed.

Say I want this default behaviour only in a certain condition:

s = Mid(s, i, IIf(condition, j, TheValue)) ' What could be TheValue?

Since length is of Variant type, I tried Empty. It didn't work. Neither did -1 and Nothing. I didn't want to duplicate to Mid call in an If-Then-Else clause or somehow else. Is this possible?

Answer 1

Here is a working sample with OP's s = Mid(s, i, IIf(condition, j, TheValue)) line

Option Explicit

Property Get TheValue(Optional RetVal As Variant)
    TheValue = RetVal
End Property

Private Sub Form_Load()
    Dim s As String
    Dim i As Long
    Dim j As Long
    Dim condition As Boolean
    
    s = "test test test"
    i = 6: j = 3
    condition = False
    s = Mid(s, i, IIf(condition, j, TheValue))         '<--- this works!
    Debug.Print s
End Sub

Notice how TheValue returns a "missing" Variant i.e. one which tests positive for IsMissing and can be used in place of optional parameters instead of not passing actual argument.