If you want to avoid autovivification, there's the autovivification module. It allows you to disable autovivification for a particular scope. Example:

use 5.010;
use strict;
use Data::Dumper;

my %rec;

{
    no autovivification;
    
    say "Oh No!(1)" if exists $rec{NOTE}{Nested};
    say "Oh No!(2)" if exists $rec{NOTE};
}

say "Oh No!(3)" if exists $rec{NOTE2}{Nested};
say "Oh No!(4)" if exists $rec{NOTE2};

print Dumper \%rec; 

__END__
Oh No!(4)
$VAR1 = {
          'NOTE2' => {}
        };

[download]

It even allows you to selectively disable it - e.g. disable autovivification for "exists", but not when storing a new value.

no autovivification qw(exists);
if (!exists $rec{NOTE}{Nested})
{
  # but this still autovivifies $rec{NOTE}={};
  $rec{NOTE}{Nested2} = 'Foo';
}

[download]

And also allows you to make autovivification warn or die.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re: gotchas with hash element autovivification by tobyink
in thread gotchas with hash element autovivification by raybies

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