Yeah, works for me as well. Perhaps your confusion is with %$hr{a} which would be trying to dereference a hashref contained in the hash %hr in the value associated with the key "a".

use Data::Dumper qw( Dumper );

$hash_a->{a} = "hello" ; 
@$hash_b{a} = "hello"  ; 
$arr_a->[0] = "hello" ; 
@$arr_b[0] = "hello" ;  

print "hash_a ", Dumper( $hash_a ), "\n";
print "hash_b ", Dumper( $hash_b ), "\n";
print "arr_a ", Dumper( $arr_a ), "\n";
print "arr_b ", Dumper( $arr_b ), "\n";

__END__

hash_a $VAR1 = {
          'a' => 'hello'
        };

hash_b $VAR1 = {
          'a' => 'hello'
        };

arr_a $VAR1 = [
          'hello'
        ];

arr_b $VAR1 = [
          'hello'
        ];
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