Static 'function' in vba/excel? - vba

Question

I just have a very simple question regarding vba.
I understand that a static variable in vba keeps its previous value rather then reseting it each time the function is called. However, I was wondering how could I have a "static function" rather than a variable. Let me clarify this with a simple code:
Function Alt(Soc1 As Double)
Static D As Integer
If Soc1 >= 40 Then
Alt = 0
ElseIf Soc1 <= 30 Then
Alt = 1
End If
End Function
Here I would like the variable-function Alt to keep its previous value so that I get a sort of "hysteresis" behaviour. However if I add:
Static Alt As Integer
I get an error when calling the function Alt().
Also if I add a line such as:Alt = D while D is decalred as static I get an alternating value of Alt (1,0,1,0,1,0 ..) instead of (1,1,1,1) if active or (0,0,0,0) if not.
How should I tackle this simple issue? Any help would be appreciated.
Thank you in advance!

Answer 1

If I've got you, not sure it does what you need. :)
Option Explicit
Public intReturnToHold As Double
Sub call_function()
Debug.Print Alt(2, intReturnToHold)
End Sub
Function Alt(Soc1 As Double, Optional ByRef intHoldAlt)
Static D As Integer
Alt = intReturnToHold
If Soc1 >= 40 Then
Alt = 0
ElseIf Soc1 <= 30 Then
Alt = 1
End If
intHoldAlt = Alt
End Function

Answer 2

Thank you Nathan for your answer. Altough I don't really understand your code I believe I get the idea of it but it did not work.
I have tried my previous idea again and for some reason it worked this time, here is the code;
Function Alt(Soc1 As Double)
Static D As Integer
If Soc1 >= 40 Then
D = 0
ElseIf Soc1 <= 30 Then
D = 1
End If
Alt = D
End Function
I have previously tired the EXACT same code and the results were as I said in my question "alternating" between 1 and 0 (when active) but now are constant 1 (when active).

Answer 3

I'm not 100% sure what you are asking, but if you want a function to compute just once and then retain its value, you could do something like this:
Function Alt(Soc1 As Double) As Long
Static D As Long
Static Called As Boolean
If Called Then
Alt = D
Exit Function
End If
If Soc1 >= 40 Then
D = 0
ElseIf Soc1 <= 30 Then
D = 1
End If
Called = True
Alt = D
End Function
On the other hand, if your goal is to have a function which, once it takes on the value 1 never resets to 0, something like this would work:
Function Alt(Soc1 As Double) As Long
Static D As Long
If D = 1 Then
Alt = D
Exit Function
End If
If Soc1 >= 40 Then
D = 0
ElseIf Soc1 <= 30 Then
D = 1
End If
Alt = D
End Function