Thanks, all who replied. However, I forgot something while trying to narrow it down. One of the hashes is a tie()d array, and that's what goes wrong for some reason.

So much for trying to find out where it goes wrong. Here's the real script: 
2;0 juerd@ouranos:~$ rm karmatest
2;0 juerd@ouranos:~$ perl test.pl
Use of uninitialized value in addition (+) at test.pl line 31.
2;0 juerd@ouranos:~$ cat test.pl
#!/usr/bin/perl -w

package Karma;
use GDBM_File;
use strict;

sub new($$){
    my ($prot, $file) = @_;
    my $self = { hash => {} };
    $self->{object} = tie %{ $self->{hash} }, 'GDBM_File', $file, GDBM
+_WRCREAT,
0640;
    bless $self, $prot;
    return $self;
}

sub resolve($$){
    my ($self, $subject) = @_;
    $subject = lc $subject;
    my $recur = 0;
    if (defined $self->{hash}{$subject}){
        while ($self->{hash}{$subject} =~ /^S:(.*)/){
            $subject = 'ERECURSIE', last if ++$recur > 10;
            $subject = lc $1;
        }
    }
#   The next line was put in to work around the warning.
#   $self->{hash}{$subject} = 0 unless defined $self->{hash}{$subject}
+;
    return \ $self->{hash}{$subject};
}

sub incr($$;$){
    my ($self, $subject, $d) = @_;
#line 31
    return ${ $self->resolve($subject) }  +=  defined($d) ? $d : 1;
}

sub decr($$;$){
    my ($self, $subject, $d) = @_;
    return ${ $self->resolve($subject) }  -=  defined($d) ? $d : 1;
}

sub get($$){
    my ($self, $subject) = @_;
    my $foo =  ${ $self->resolve($subject) };
    print "BLAAT: $foo\n";
    return $foo;
}

sub set($$$){
    my ($self, $subject, $new) = @_;
    return ${ $self->resolve($subject) }  =  $new;
}

sub reorganize($){
    $_[0]->{object}->reorganize();
}
1;

package main;

my $karma = Karma->new('karmatest');
$karma->incr('foo'); # foo must not exist

[download]

I'm sorry to have disappointed you by leaving out a very important part. 

2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$

[download]

In reply to Re: Autovivification not working? by Juerd
in thread Autovivification not working? by Juerd

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