Consider the following script:

#!/usr/bin/perl

use strict;
use warnings;
use Test::More;
use Data::Dumper;

my $hash = {
    '50' => [ 1 ]
};
print Dumper $hash;

is(keys %{$hash},            1, q/keys %{$hash} is 1/);
is(scalar @{$hash->{'50'}},  1, q/$hash->{'50'} is 1/);
is(scalar @{$hash->{'100'}}, 0, q/$hash->{'100'} is 0/);

print Dumper $hash;

done_testing();

[download]

With Perl 5.24.3 it runs to the end and all tests pass, even though I would expect that it dies with an "Can't use an undefined value as an ARRAY reference" error when it tries to dereference $hash->{'100'} which indeed does not exist.

Compare with 

#!/usr/bin/perl

use strict;
use warnings;

my $hash = {
    '50' => [ 1 ]
};

print scalar @{$hash->{'100'}};

[download]

which dies with the expected error.

Under Perl 5.16 the first program also dies with the expected error. (This is how we initially noticed the problem: a program that was developed on 5.22+ needed to be ported to Centos 7 which has 5.16, and the tests began to fail there.)

What is going on here?

(Errata: Now I've ran with more Perl versions (perversions), and it doesn't die under perl 5.22 and above, but dies as expected under perl 5.20 and below)

In reply to Why doesn't this die with "Can't use an undefined value as an ARRAY reference"?" by kikuchiyo

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