#!/usr/bin/perl -CSDA

use utf8; 
use strict; 
use warnings; 
no warnings qw{uninitialized numeric}; 
no autovivification; #  qw{fetch exists delete store}; 
use Data::Dumper; 

print "\n\ninitialize data structures, no autovivification\n"; 
my $n = { 
	a => [1, 2 ], 
	b => [3, 4], 
}; 
$$n{'x'}{'y'}{'z'} and die; 
$$n{'x'}{'y'}[0] and die; 
$$n{'x'}{'y'} and die; 
$$n{'x'} and die; 
print "so far, so good, no 'x' autovivified:\n"; 
print Dumper $n; 

# "Can't use an undefined value as an ARRAY reference": 
# @{$$n{'x'}} and die;  

print "\n\nnow the same but in loop:\n"; 
for my $e (@{$$n{'x'}}) { 
}
print "why 'x' autovivified?\n"; 
print Dumper $n; 

print "\n\nnow the same but in loop:\n"; 
for my $e (@{[ $$n{'y'} ]}) { 
}
print "why 'y' NOT autovivified?\n"; 
print Dumper $n; 


1; 

##</code><code>##



initialize data structures, no autovivification
so far, so good, no 'x' autovivified:
$VAR1 = {
          'a' => [
                   1,
                   2
                 ],
          'b' => [
                   3,
                   4
                 ]
        };


now the same but in loop:
why 'x' autovivified?
$VAR1 = {
          'x' => [],
          'a' => [
                   1,
                   2
                 ],
          'b' => [
                   3,
                   4
                 ]
        };


now the same but in loop:
why 'y' NOT autovivified?
$VAR1 = {
          'x' => [],
          'a' => [
                   1,
                   2
                 ],
          'b' => [
                   3,
                   4
                 ]
        };