Binaryworld - Items of ParamArray can be Missing ... [ VB -> Language ]

When using the ParamArray keyword within a procedure, always remember that when the procedure is invoked from elsewhere in the program one of the argument might be omitted, and you should keep this into account. Here is an example of a routine that uses ParamArray:

Click here to copy the following block

Function Max(ParamArray args() As Variant) As Variant
Dim result As Variant, index As Integer
result = args(LBound(args))
For index = LBound(args) + 1 To UBound(args)
If result < args(index) Then result = args(index)
Next
Max = result
End Function

The above routine works fine, but only if the programmer doesn't omit any argument in the list. If you recall the function as in:

Print Max(1, , 3)

the function will raise a "Type Mismatch" error. Here's a better version, that also accounts for missing arguments:

Click here to copy the following block

Function Max(ParamArray args() As Variant) As Variant
Dim result As Variant, index As Integer
For index = LBound(args) To UBound(args)
  If IsMissing(args(index)) Then
   ' ignore this argument
  ElseIf IsEmpty(result) Then
   ' the first time we set a possible return value
   result = args(index)
  ElseIf result < args(index) Then
   result = args(index)
  End If
Next
Max = result
End Function

Also, remember that to a Variant argument you can pass almost anything, including objects and arrays. If you really want to create a general-purpose routine you should account for these cases too.