Guarding against uninitialized variables RFC

[Iain Sandoe]

> On 21 Jun 2026, at 23:03, Jose E. Marchesi <jemarch@gnu.org> wrote:
> 
> 
>> Good day everyone,
>> 
>> After 10 days away from almost everything to do with computers in order to
>> concentrate on Important Stuff (like beaches), I'm back prodding van
>> Vliet's transput.
>> 
>> The open, establish and create procedures will fail with a non-zero return
>> code if they cannot establish the linkage between File, Channel, Book and
>> the operating system file.  However this can leave the nonpublic Book
>> variable in an uninitialized state.
>> 
>> Of course, I can initialize the Book variable to some pattern that I can
>> later interpret as meaning no linkage was created; and I can check wherever
>> that Book variable is used to make sure it has a valid linkage.
>> 
>> But I don't believe there is a way to detect uninitialized variables other
>> than this.
>> 
>> Does anyone have any suggestions?  Thanks in advance!
> 
> I think there is no way.
> 
> In strict Algol 68 the value actually held by uninitialized variables is
> undefined.
> 
> In GNU Algol 68 uninitialized variables all have a predictable value: 0
> for int, 0.0 for real, " " for char, etc.
> 
> But that will not really help to detect uninitialized variables.
> 
> I would look to declare a no_book identifier with some distinguishable
> value ascribed to it, then get the books initialized to it, then check
> for it before accesses.  Alternatively, you could add an additional
> book_initialized boolean..
> 

You might want to look at what C++ is doing with “Erroneous behaviour” 
and marking vars as uninitilised.  There’s no really good value that can
be used to indicate this - some “on the side” meta-data seems needed.
Perhaps a bit on a var decl would be worth allocating.

"maybe uninitialised" warnings are not the most popular...

Iain