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(\@_)) });

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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!

Replies are listed 'Best First'.
Re: Death to auto-vivification
by clinton (Priest) on Mar 03, 2008 at 12:25 UTC
    You could also check out Data::Diver by tye, for which "Dive() absolutely refuses to autovivify anything".
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Re: Death to auto-vivification
by bobf (Monsignor) on Mar 03, 2008 at 19:21 UTC

    You may find Hash::Util or Readonly interesting. I haven't used either but I'm sure other monks could chime in on their pros and cons. A Super Search might point you in the right direction, too.

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      I'm a fan of Hash::Util when working with hash-based objects, myself. I tend to use init routines that look like this (to make it impossible to accidentally create a hashkey that's not supposed to be there): 
      use Hash::Util qw( lock_keys unlock_keys );

sub init {
  my $self = shift;
  my $args = shift;
  unlock_keys( %{ $self } );

  my @attributes = qw(
                       something_or_other
                       another_something
                      );

  foreach my $field (@attributes) {
    $ATTRIBUTES{ $field } = 1;
    $self->{ $field } = $args->{ $field };
  }

  lock_keys( %{ $self } );
  return $self;
}

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[d/l]

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