#!/usr/bin/perl

use strict;
use warnings;
use Tie::Hash::DarmstadtPM;

tie my %hash,'Tie::Hash::DarmstadtPM',sub{$_[0] + $_[-1]};

my $foo = [2,3];
my $bar = [4,5];

print $hash{$foo},"\n";
print $hash{$bar},"\n";