Subject: bug#45570: [PATCH] system: Assert, that user and group names are unique.

From: Ludovic Courtès <[email-masked]>
Date: Wed, 06 Jan 2021 14:32:10 +0100

Hi,

Leo Prikler <[email-masked]> skribis:

>> > +    ((first . rest)
>> > +     (if (member first rest =) ; (srfi srfi-1) member
>> > +         (cons first (find-duplicates rest =))
>> > +         (find-duplicates rest =)))))
>> 
>> Note that this is quadratic; it’s fine as long as we don’t have “too
>> many” users, which may be the case in general.
> It is indeed quadratic, but would there even be an n log n solution?
> I've once done an n log n sort+delete-duplicates!, perhaps that'd be a
> nicer solution here?

You could first build a hash table or vhash or set with all the names,
then traverse again the list of names and check whether they’re in that
table.  That’d be linear (assuming the table is well balanced), but the
constant factor would be higher.

>>   (define (assert-unique-account-names users)
>>     (match (find-duplicates things …)
>>       (() #t)
>>       (lst
>>        (raise (formatted-message (G_ "the following accounts appear
>> more than once:~{ ~a~}~%"
>>                                  lst))))))
>> 
>> ?
> That'd be weird for duplicate duplicates, hence just reporting the
> first.

You could do (delete-duplicates lst) in the message above?

Thanks,
Ludo’.