I changed a folderitem's tests and am confused. I always understood this second test would fail if the folderitem was not Nil but also did NOT exist.
I have a property that is part of a module and it is a global property.

IniHerd.ThPrefsF

ThPrefsF is the folderitem for the preferences file.
At the moment I am confused because I declared a few hundred lines before

IniHerd.ThPrefsF = IniHerd.ThColl.Child("PrefsFile.ini")

and in this case it doesn't exist, but is only the location.
I have these lines of code that according to my understanding should work but fail when exists = false

If IniHerd.ThPrefsF <> Nil And IniHerd.ThPrefsF.Exists Then
//will succeed if it fulfills both tests
ElseIf IniHerd.ThPrefsF = Nil And IniHerd.ThPrefsF.Exists = False Then
//Will fail if either is not true
End If//If IniHerd.ThPrefsF <> Nil And IniHerd.ThPrefsF.Exists Then

Is my logic correct?

So just to be sure: Can a folderitem be Not Nil and exists=false?
Or maybe I should make my last test be only exists=false?

Thanks for confirming. Grumble

Grumble?

I have these lines of code that according to my understanding should work but fail when exists = false

Thats quite confusing code, despite the logic.
Assuming you want to write the file, you can ignore whether it exists or not and just write it.
If you want to append, then yes you need to know if it exists already. But a prefs file is usually rewritten in full.

If IniHerd.ThPrefsF <> Nil then
     // you have created a badly formed folderitem in memory.. stop!
else
   //folderitem seems OK
    // create a textoutputstream and write to it
end if

if you want to append:

If IniHerd.ThPrefsF <> Nil then
     // you have created a badly formed folderitem in memory.. stop!
else
   //folderitem seems OK
if IniHerd.ThPrefsF.exists then
// open a textoutputstream for appending and write to it
else
    // create a textoutputstream and write to it
end if
end if

This code doesnt contain any exception handlers for inability to write (such as trying to write to a read-only device)

To hopefully further clarify what Dave said...

A folderitem cannot be Nil. Nil means you haven't assigned a Folderitem to the property.

.Exists checks whether a file or folder exists at the location pointed to by a folderitem.

Checking .Exists on a Nil Object will just raise a NilObjectException.

An example of what Dave is saying:

dim f as FolderItem

f = SpecialFolder.Home.Child("this directory doesn't exist yet")

'f is not nil

f = SpecialFolder.Home.Child("this directory doesn't exist yet").Child("this directory also doesn't exist yet")

'f is nil

Ok, to clarify... Nil means you've either not assigned a value or assigned nil to the value.

If it is nil it is not a folderitem. A folderitem is an object. I'm just trying to clarify the difference between the property and the value. Nil means there is no object in the property.

@Scott G f = SpecialFolder.Home.Child("this directory doesn't exist yet").Child("this directory also doesn't exist yet")

Right, exactly what I'm saying. FolderItem.Child() is a function that returns either a folderItem OR Nil.

@Dave S @jim m Right, exactly what I'm saying. FolderItem.Child() is a function that returns either a folderItem OR Nil.
This IS a true statement

Hmm, I think it's a little better to say it always returns a FolderItem, but that sometimes the FolderItem it returns is nil.

Side nore: there's actually an ineresting issue in Xojo which is that doing a copmarison using "= nil" and "is nil" behave differently in some situations. I think that "= nil" will invoke operator_convert but "is nil" will not. (citing this from memory, I may have it mixed up ).