Apparently, I have been doing something wrong for years, or I missed a change to Perl recently. I saw this code in an answer today: 
#!/usr/local/bin/perl

use strict;
use warnings;
use Data::Dumper;
$Data::Dumper::Indent   = 1;

my @array1 = qw{rose orange green};
my @array2 = qw{blue red};

my %hash;
push @{$hash{first}}, \@array1, \@array2;
print Dumper \%hash;

[download]
I was under the impression that this code will not run. Specifically, because of the array deref. $hash{first} should return undef, and I did not think you could dereference an undefined value and magically get an array reference, but the code runs. I had always used: 
$hash{first} ||= [];
push @{ $hash{first} },'foo';

[download]
I am sure (in my own mind, at least) that I would get run-time errors if I left out the initialization.
Can someone enlighten me as to where my cognitive breakdown lies?


-pete
"Worry is like a rocking chair. It gives you something to do, but it doesn't get you anywhere."

In reply to autovivication gonna make me lose my mind by dreadpiratepeter

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