vba passing dynamic array to class - vba

Question

i have an issue with dynamic arrays being passed to class byVal instead byRef, so simplified class, cArray
Option Explicit
Private mArray() As String
Public Sub init(ByRef iArray() As String)
mArray = iArray
End Sub
Public Property Get count() As Long
count = UBound(mArray) - LBound(mArray)
End Property
Public Property Get item(iIndex As Long) As String
item = mArray(iIndex)
End Property
and simple function in module
Private Sub arrTest()
Dim arr() As String, cont As cArray
ReDim arr(0 To 1)
arr(0) = "value0"
arr(1) = "value1"
Set cont = New cArray
cont.init arr
arr(1) = "newValue1"
Debug.Print cont.item(1), arr(1) 'will print value1, newValue1 even though is expected to be same
ReDim Preserve arr(0 To 2)
arr(2) = "value2"
Debug.Print cont.count 'will print 1
End Sub
so, question is, is this bug? normal behavior? something else?

Answer 1

Actually, the array is passed by reference. The problem comes at the assignment.
In VBA assigning one array variable to another array variable or one string variable to another string variable creates a copy though there are ways around this using Variants or CopyMemory, for example. If you're interested, drop a comment.
I can demonstrate this by using VarPtr to get the actual addresses for comparison. Let's add a few lines to your code...
cArray
Option Explicit
Private mArray() As String
Public Sub init(ByRef iArray() As String)
Debug.Print "The address of the function parameter is: " & VarPtr(iArray(0)) '<----- add this line
mArray = iArray
Debug.Print "The address of the mArray class member is: " & VarPtr(mArray(0)) '<----- add this line
End Sub
Public Property Get count() As Long
count = UBound(mArray) - LBound(mArray)
End Property
Public Property Get item(iIndex As Long) As String
item = mArray(iIndex)
End Property
mdlMain
Private Sub arrTest()
Dim arr() As String, cont As cArray
ReDim arr(0 To 1)
arr(0) = "value0"
arr(1) = "value1"
Debug.Print "The address of the newly dimensioned and initialized arr is: " & VarPtr(arr(0)) '<----- add this line
Set cont = New cArray
cont.init arr
arr(1) = "newValue1"
Debug.Print cont.item(1), arr(1) 'will print value1, newValue1 even though is expected to be same
ReDim Preserve arr(0 To 2)
arr(2) = "value2"
Debug.Print cont.count 'will print 1
End Sub
When I run this, I get (the memory addresses will likely be different for you):
The address of the newly dimensioned and initialized arr is: 192524056
The address of the function parameter is: 192524056 The address of the
mArray class member is: 192524040
value1 newValue1 1
So you can see that the actual function parameter WAS passed by reference, but the assignment created a copy.