How to make VBA function "VBA only" and disable it as UDF - excel

Question

I'm writing a VBA function which I want to be publically available in other VBA modules within the same document, however I don't want it to be available as a UDF (User defined function).
If I use the public access modifier however my function is also be available as a UDF-formula that can be called from the cells within the workbook. I don't want this.
Is there an access modifier or other way that can help me obtain this "VBA only" behaviour?
Kind regards

Answer 1

If you use Option Private Module in the module in which the function appears, the function can be declared as Public and used in any of your other modules within your VBA project, but won't be accessible by other applications or projects, including Excel itself.

Answer 2

This will return a #VALUE error if used in Excel.
Function VBAOnly() As Variant
If TypeName(Application.Caller) <> "Range" Then
VBAOnly = 1 'or some other return value
Else
VBAOnly = CVErr(xlErrValue)
End If
End Function

Answer 3

There's a little bit of confusion among answers, so here's a more encompassing explanation:
Technically... all functions in the standard VBA Modules can be called if the exact formula is entered. Even Formulas in Private Functions within Private Modules
Example
Option Private Module
Private Function hiddenEverythingExample() As String
hiddenEverythingExample= "NOPE!!!"
End Function
Will still return a value if a cell has =hiddenEverythingExample()
However, I believe the objective of the OP was to avoid having the itellisense populate these functions in the Excel Formula bar.
The most frequent way I accomplish this is create a specific Module for all VBA-Only functions and put Option Private Module in the module definition (area above the functions).
This ensures all functions in this module will NOT appear in itellisense, but still be accessible to other modules along with itellisense.
Defining asPrivate Function also accomplishes this, but then the function is scoped exclusively to that Module, which may or may not be the requirement.
Note that YowE3K infers that a function must be both Private Function AND Option Private Module, but only one OR the other is necessary to eliminate the itellisense.

Answer 4

Instead of writing a Function, write a Sub, and set the return via a ByRef argument. This way your function will be invisible to Excel (except via Alt F8, or Developer tab > Macros) and won't appear in Excel's intellisense.
Instead of
Function Add(Num1 As Double, Num2 As Double)
Add = Num1 + Num2
End Function
use
Sub AddInvisible(ByRef Result As Double, Num1 As Double, Num2 As Double)
Result = Num1 + Num2
End Sub
Note
That ByRef is not strictly necessary (since arguments are by default by reference in VBA) but it serves as a useful reminder that Result carries the return value.
You will need to make the necessary changes to your code, for example:
z = Add(x,y)
would become
AddInvisible z,x,y
as demonstrated below:
Sub DemoAddInvisible()
Dim Num1 As Double
Dim Num2 As Double
Dim Result As Double 'Result initialises to 0
Num1 = 1
Num2 = 2
AddInvisible Result, Num1, Num2
MsgBox Result ' See that Result has become 3
End Sub
A downside of all this is that the new code is somewhat harder to understand.

Answer 5

pass a parameter that only allows the function to run if a "magic* value is given to it.
Example - This will give the error #NAME! unless you know what the key is:
Function VBAOnly(key As Long)
If key <> 12345 Then
VBAOnly = CVErr(xlErrName)
Exit Function
End If
VBAOnly = True
End Function

Answer 6

Using the Private modifier should only allow the execution in the module the function exists in.