$hash{'a', 'b'}
[download]

use strict;
use Tie::Hash;
package Tie::HashNKeys;
use base 'Tie::StdHash';

sub TIEHASH {
my $class = shift;
bless {}, $class;
}

sub STORE {
 $_[0]->{ join $;, sort split /$;/, $_[1] } = $_[2];
}

sub FETCH {
$_[0]->{ join $;, sort split /$;/, $_[1] };
}

package main;
use Data::Dumper;

$; = '~'; # so it can be seen
tie my %hash, 'Tie::HashNKeys';
$hash{'csUsers','csGroups'} = 'foo';
print $hash{'csGroups','csUsers'};   ## prints 'foo'
print Dumper(\%hash);
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Update from the front lines: well, it seems to be working part of the time. Revelation #1:

$hash{$foo,$bar}

does not work the same as

$hash{  @mykeys{'foo','bar'}  } I'll post an additional reply if i can't get the rest of it working...

I don't think you need to use anything special like a tie or otherwise for this. The hash key can be an array (not an arrayref), which you can use to emulate multi-key'd hashes without the need for any special coding. See my node An interesting oddity with hashes for more details.

my %hash;
$hash{ 3,4 } = "array";
$hash{ 3 } = "three";
$hash{ 4 } = "four";    # no collisions!
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A neat trick to be sure. However I need it so that $hash{3,4} and $hash{4,3} result in pulling the same value.