False Positive "Parameter can be passed by value"

[majkaz]

Rubberduck version information
Version 2.5.1.5557
OS: Microsoft Windows NT 10.0.14393.0, x64
Host Product: Microsoft Outlook x86
Host Version: 16.0.4266.1001
Host Executable: OUTLOOK.EXE

Description
As part of my old code, currently in refactoring, a MailItem is passed ByRef to a function and the function manipulates the subject if a condition is met.
Inspection shows "Parameter can be passed by value".

The complete function for review:

Private Function DeferedDaysFromSubject(ByRef oMail As Outlook.MailItem) As Single
    
    Dim NumBegin As String
    NumBegin = GetNumericBeginning(oMail.Subject)
    
    If NumBegin <> vbNullString Then
        
        DeferedDaysFromSubject = VBA.CSng(NumBegin)
        
        Dim mailSubject As String
        mailSubject = VBA.Trim(VBA.Mid$(oMail.Subject, VBA.Len(NumBegin) + 1))
        oMail.Subject = mailSubject
        
    End If

End Function

In my understanding, this one is false positive.

[retailcoder]

Hi! Thanks for the feedback!

The reference itself is not being Set, so the result is legitimate, and the parameter can (arguably should) indeed be passed by value. oMail.Subject = ... is not altering the object reference ByRef/ByVal is referring to, only a property of that object; passing the reference ByVal would guarantee that the function cannot alter that reference as a side-effect.

Try adding Set oMail = Nothing just before End Function: with ByRef the caller probably blows up with error 91 now, with ByVal only the local pointer was (needlessly) nullified, and the calling code carries on without flinching!

[majkaz]

My mistake, the issue can be closed.

I know I am dating myself, but I swear I am aware of the situation when referencing an object since the time I had to change my macros from WordBasic to VBA. Looking at the spaghetti mess I have accumulated in years, I had a brain freeze.