Initializing a static variable in VBA with non-default value - vba

Question

Static variables in VBA are simple enough:
Public Sub foo()
Static i As Integer
i = i + 1
Debug.Print i
End Sub
outputs (when called multiple times):
1
2
3
...
The problem is, VBA does not support initializing a variable on the same line as the declaration (not counting using : to put two lines on one):
Public Sub foo()
Dim i As Integer = 5 'won't compile!
Dim j As Integer
j = 5 'we have to do this instead
End Sub
This clashes with static variables:
Public Sub foo()
Static i As Integer 'we can't put an initial value here...
i = 5 'so this is how we'd usually initialize it, but...
i = i + 1
Debug.Print i
End Sub
You can probably see what happens - The very first thing the variable does every time foo is called is set itself back to 5. Output:
6
6
6
...
How can you initialize a static variable in VBA to a value other than its default? Or is this just VBA dropping the ball?

Answer 1

One way to do this if you want to keep the static semantics and not switch to a global is to sniff the default value and then set the initial condition:
Static i As Integer
if (i = 0) then i = 5
Safer alternative would perhaps be
Static i As Variant
if isempty(i) then i = 5
Or
Public Sub foo(optional init as boolean = false)
Static i As Integer
if init then
i = 5
exit sub
endif
You could probably also create a class with a default property and use class_initialize but that's probably a bit over-fussy.

Answer 2

I had the same issue in VB6, where it's exactly the same, and I like the Microsoft recommendation most:
Sub initstatic ()
Static Dummy, V, I As Integer, S As String
' The code in the following if statement will be executed only once:
If IsEmpty(Dummy) Then
' Initialize the dummy variant, so that IsEmpty returns FALSE for
' subsequent calls.
Dummy = 0
' Initialize the other static variables.
V = "Great"
I = 7
S = "Visual Basic"
End If
Print "V="; V, "I="; I, "S="; S
' Static variables will retain their values over calls when changed.
V = 7
I = I + 7
S = Right$(S, 5)
End Sub

Answer 3

I solved it as follows using a static boolean to indicate if you are entering the function for the first time. This logic should work for other situation as well, i think
Private Sub Validate_Date(TB as MSForms.TextBox)
Static Previous_Value as Date
Static Not_First_Time as Boolean
if Not_First_Time = False Then
Previous_Value = Now
Not_First_Time = True
endif
if IsDate(TB.Value) = False then TB.Value = Previous_Value
Previous_Value = TB.Value
End sub

Answer 4

The use of a Boolean to flag something as already initialized functions correctly in normal use but has an unexpected side effect when using the debugger. bIsInitialized is NOT reset to False when the VBA projuect is re-compiled. When the initialization code (or the constants the code uses) is changed changed, the thing being initialized will not be re-initialized while using the debugger.
One work-around is to set a breakpoint at the statement "If (Not bIsInitialized) Then" and add bIsInitialized as a watch variable. When the breakpoint is reached the first time, Click on the value and change it to false, remove the breakpoint and use F5 to continue. There may be a better work-around that uses something that is reliably reset by recompiling the project, but since the documentation for VBA says that the Boolean would be re-initialed after going out of context and all code stopping, there's no way to know if that behavior was version dependent. Not reinitializing the block of memory associated with the routine appears to be a performance optimization.
Static bIsInitialized as Boolean
Static something_time_consuming_to_initialize
If (Not bIsInitialized) Then
initialize something_time_consuming_to_initialize
bIsInitialized = True
End If