perlmeditation
tphyahoo
Here's a little snip I put together messing around with autovivification. Perhaps some monks that feel queasy about this topic may find it useful.
<p>
For a more in depth tutorial on the topic [id://445927] may be of interest. Cheers :)
<code>
use strict;
use warnings;
use Test::More qw(no_plan);
use Data::Dumper;
my %hash = (a => 'a', b => 'b');
ok( ! exists($hash{c}), "hash -- c doesn't exist");
ok( ! exists($hash{c}), "hash -- c still doesn't exist");
ok( ! defined($hash{c}), "hash -- c not defined either");
my $hashref = { %hash };
ok( ! exists($hashref->{c}), "hashref -- c doesn't exist");
ok( ! exists($hashref->{c}), "hashref -- c still doesn't exist");
ok( ! exists( $hashref->{c}->{d} ), "hashref, deeper -- c->{d} doesn't exist");
ok( ! exists( $hashref->{c}->{d} ), "hashref -- c->{d} still doesn't exist");
ok( ! exists($hashref->{c}), "hashref -- c still doesn't exist"); #fails. c does exist.
ok( ! defined($hashref->{c}), "hashref -- c still doesn't exist"); #fails. c is an empty hashfref, which is something other than undef.
</code>