You could use the array address/reference (in string form) as key. It can be questioned if this is really useful, because another array with identical content results in an different reference and therefore different key:

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my @a = (1,2,3);
my %h;

$h{\@a} = "value";

my @b = @a;
$h{\@b} = "other value";

print Dumper \%h;

__END__

$VAR1 = {
          'ARRAY(0x84df0e0)' => 'other value',
          'ARRAY(0x847c540)' => 'value'
        };
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Like other posts pointed out: You could create a string from the array (like join "\0", @array) and use this as key or maybe use a Tie package. But this all depends on what you really want to do.