What is the benefit of using ParamArray (vs a Variant array)? - vba

Question

I've used the ParamArray statement for years when I wanted to accept a variable number of arguments. One good example is this MinVal function:
Function MinVal(ParamArray Values() As Variant)
Dim ReturnVal As Variant, v As Variant
If UBound(Values) < 0 Then
ReturnVal = Null
Else
ReturnVal = Values(0)
For Each v In Values
If v < ReturnVal Then ReturnVal = v
Next v
End If
MinVal = ReturnVal
End Function
' Debug.Print MinVal(10, 23, 4, 17)
' 4
This could be re-written without the ParamArray as:
Function MinVal(Optional Values As Variant)
Dim ReturnVal As Variant, v As Variant
If IsMissing(Values) Or IsNull(Values) Then
ReturnVal = Null
Else
ReturnVal = Values(0)
For Each v In Values
If v < ReturnVal Then ReturnVal = v
Next v
End If
MinVal = ReturnVal
End Function
' Debug.Print MinVal(Array(10, 23, 4, 17))
' 4
Note in the second example use of the Array() function in the call to MinVal.
The second approach has the advantage of being able to pass the parameter array to another function that also accepts arrays. This provides flexibility if I ever wanted to be able to pass the parameter array in MinVal on to some other function.
I've begun thinking I should always favor this approach and just stop using ParamArray altogether.
One could argue that using ParamArray makes for more explicitly readable code. However, there's no advantage in compile-time checks because ParamArray must be an array of Variants. Can anyone offer a compelling reason to ever use ParamArray?

Answer 1

Most of my ParamArray functions have std Array versions that do the heavy lifting like this:
Private Sub Command2_Click()
Process 1, 2, 3
End Sub
Private Sub Process(ParamArray A() As Variant)
ProcessArray CVar(A)
End Sub
Private Sub ProcessArray(B As Variant)
Debug.Print UBound(B)
End Sub
This does not work for output params though, so yes replacing ParamArray with Array gets really fast very inconvenient for output params.

Answer 2

You've already noted one reason to use Paramarray - sometimes it makes code more clear. In fact, I think in your own example that:
Debug.Print MinVal(10, 23, 4, 17)
is preferable to:
Debug.Print MinVal(Array(10, 23, 4, 17))
Of course, how "compelling" this is is a matter of opinion. Code clarity rarely matters much in small examples, but in a large code base it can add up to be very important.
If you're using VBA with Excel, then there is a somewhat-compelling reason to use ParamArray. Consider a UDF of the following form:
Public Function mungeRanges(ParamArray ranges())
'do something with a bunch of ranges
End Function
The built-in Excel function MIN works like this in fact - you can pass in multiple arguments, including ranges or arrays, and it looks through all of them to find the smallest individual value. Anything that follows a similar pattern would need to use ParamArray.