How to reserve an array in a public function?

[tinfanide]

Sub test()

Dim x As Integer

For x = 0 To 3
    MsgBox (ReturnRandomNumber(0, 3, x))
Next x

End Sub

Public Function ReturnRandomNumber(lower As Integer, upper As Integer, turn As Integer) As String
    
    Dim n As Integer, arr() As Variant
    
Redo:
    n = Int((upper - lower + 1) * Rnd + lower)
    
    ReDim Preserve arr(turn)
    
    ''' I want to store every n to check if the random number generated is repeated
    For Each a In arr
        If a = n Then GoTo Redo
    Next a
    
    ''' Within this function, the Array arr() does not store every n
    arr(turn) = n
    ReturnRandomNumber = n
    
End Function

If I move the foreach loop and the array within the sub, it can loop through the array and check if the newly generated random number is repeated.

But it does not work within a public function.

[macropod]

From the Word vba help file:

This array is fixed or temporarily locked (Error 10)

You attempted to assign a value to a Variant variable containing an array, but the Variant is currently locked. For example, if your code uses a For Each...Next loop to iterate over a variant containing an array, the array is locked on entry into the loop, and then released at the termination of the loop
...
Use a For...Next rather than a For Each...Next loop to iterate. When an array is the object of a For Each...Next loop, you can read the array, but not write to it.

[tinfanide]

Sub test()

Dim x As Integer

For x = 0 To 3
    MsgBox (ReturnRandomNumber(0, 3, x))
Next x

End Sub

Public Function ReturnRandomNumber(lower As Integer, upper As Integer, turn As Integer) As String
    
    Dim n As Integer, arr() As Variant
    
Redo:
    n = Int((upper - lower + 1) * Rnd + lower)
    Debug.Print (n)
    
    ReDim Preserve arr(turn)
    
    For a = lower To upper
        If arr(a) <> "" Then
            If arr(a) = n Then GoTo Redo
        Else
            Exit For
        End If
    Next a
    
    arr(turn) = n
    ReturnRandomNumber = n
    
End Function

But the array is still empty every the function restarts. It fails when I want the array that stores every n to check if n is duplicated.