I recently wrote some code that spent an awful lot of time making decisions and taking branches based on the contents of various entries in a hash-ref. A constant irritating source of bugs was me making typos and trying to read hash entries that didn't exist. After I'd tracked down the first three or four of these hard-to-find bugs I decided to see if I could make it easier on myself.

I found Tie::Hash::Vivify which lets you hook into auto-vivification. The author's intention was apparently to let you automatically populate hash entries when you access them. I subverted it like this: 

use Tie::Hash::Vivify;
use Carp qw(confess);
use Data::Dumper;

my $hashref = Tie::Hash::Vivify->new(sub { confess("No auto-vivifying!
+\n".Dumper(\@_)) });

[download]

so now whenever I try to read a hash entry that doesn't exist, my code dies with a stack trace (so I can tell where the error is) and shows me the parameters that were passed to FETCH (telling me what the error is).

Hurrah!

In reply to Death to auto-vivification by DrHyde

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