References in lvalue context autovivify.

%{ $a } in lvalue context is effectively %{ $a //= {} }

@{ $a } in lvalue context is effectively @{ $a //= [] }

For example, 

>perl -MData::Dumper -E"my $ref; $ref->{a}{b} = 'c'; print Dumper $x;"
$VAR1 = {
          'a' => {
                   'b' => 'c'
                 }
        };

[download]

As you can see, $x->{a}{b} in lvalue context is effectively ( ( $x //= {} )->{a} //= {} )->{b}.

You can control the behaviour using the autovivification module. (Don't file a bug report.)

In reply to Re: Strange behaviour of interpreter when dereferencing an undefined value by ikegami
in thread Strange behaviour of interpreter when dereferencing an undefined value by kejv2

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