$a // $b

##</code><code>##

defined $a ? $a : $b

##</code><code>##

$c //= $d;

##</code><code>##

$c = $d unless defined $c;

##</code><code>##

  my $ref = \%database;
  $ref = $ref->{$_} //= {} for @$fields;

##</code><code>##

    my $ref = \%database;
    foreach my $field (@$fields) {
        unless (defined $ref->{$field}) {
            $ref->{$field} = {};
        }
        $ref = $ref->{$field};
    }