Can Perl store an array reference as a hash key?

Question

Consider the following:

use strict;
use Data::Dumper;
my $hash={[\'one\',\'two\']=>[1,2]};
print Dumper($hash);
=for comment
prints....
$VAR1 = {
                 


        

Answer 1

You can serialize the data structure (e.g. with Data::Dumper or other similar tool) and use the string as a hash key:

my $hash = {
    Dumper(['one','two']) => [1,2],
};

Eval the key to get the data structure back.

Answer 2

No, a normal (non-tied) Perl hash can only have strings as keys. Anything else - arrayrefs, objects, whatever - will be stringified if used as a hash key, which leaves the hash key unusable as whatever non-string thing you originally had.

Hash::MultiKey uses the magic of tie to sidestep this restriction.

Answer 3

Hash::MultiKey

Answer 4

What is the need here? Why would you be looking up a hash element by an array? It seems a case for a HoH, like:

use strict;
use warnings;
use Data::Dumper;
my $hash = { one => { two => [1,2] } };
print Dumper($hash);

prints

$VAR1 = {
          'one' => {
                     'two' => [
                                1,
                                2
                              ]
                   }
        };

especially since you will be splitting the array back into its elements later. To check for existence something like:

if (exists($hash->{one}) && exists($hash->{one}{two}))

the && is needed as

if (exists($hash->{one}{two}))

would autovivify $hash->{one} if it didn't exist.