Kevin's Weblog

Can you spot the bug in this code?

use strict;
use constants { STATE_A => 0,
                STATE_B => 1,
                STATE_C => 2,
              };

...

if ($state == STATE_A) {
  do_a();
} elsif ($state == STATE_B) {
  do_b();
} elsif ($state == STATE_C) {
  do_c();
} else {
  die("bad state: $state");
}

Okay, actually there are a couple bugs:

• The code doesn’t use warnings. This might not seem like a bug to some except...
• Perl numifies undef to 0, so the first condition passes when $state is undefined, instead of dying. And, since you weren’t using warnings it’s not clear that this code is the culprit when other code starts subtly misbehaving.

So people don’t think I only pick on other people’s code, I’ll disclose that I wrote the state-handling code. However, I was not the person who failed to turn on warnings.