Yes, I agree that using undefined behaviour is bad style. That's an extremely valid point. I try at all costs to avoid such practices nowadays. But on the flipside, in Perl many things are undefined. Abigail-II has pointed out in the past that even $i = $i++; has undefined outcome, although all would agree that $i should not increment. The full debate started innocently here shows that there are many undefined parts to the very simplist of code. Yet most wouldn't complain such code's use.

And I definitely agree that this should be cleared up. The point I was (poorly) trying to get at that this should not be fixed now. We're going to break pretty much the entire of Perl5 when Perl6 is released. We could sort out substr's odd behaviour then, and no harm will come of it.

If this glitch was brought to attention a few years ago then I would have fully advocated a bug fix. But with it so late in the day now for Perl5, I geniunely believe the advantages of fixing this problem will be greatly outweighed by the problems it will cause. Perl5 is considered warty - and Perl6 is a fixup of those warts (with a few new groovy features added, naturally). I think it would make much more sense to just define this as it for Perl5 is in perldoc -f substr, and clean it in Perl6.

tlhf
Update: Slight typo; final $i was originally $i++;