#!/usr/bin/perl -CSDA

use utf8; 
use Modern::Perl qw{2017}; 
no autovivification qw{fetch store exists delete}; 

my $h = {
	'a' => {
		'p' => 2,
		'q' => 3,
	},
};

print "perl ver $]:\n"; 
$$h{a} and print "a ok\n"; 
! $$h{b} and print "b not\n"; 
! $$h{a}{x} and print "a/x not\n"; 
! $$h{a}{x}{z} and print "a/x/z not\n"; 



perl ver 5.024001:
a ok
b not
a/x not
a/x/z not


perl ver 5.028001:
a ok
b not
a/x not
Can't vivify reference at ./atest line 18.


##</code><code>##

 
ver 5.24 good way: 

! $$h{a}{x}{z} and print "a/x/z not\n"; 



ver 5.28 good (?) way: 

! ( $$h{a} && $$h{a}{$x} && $$h{a}{x}{z}) and print "a/x/z not\n";   # ?? any better idea?