#!/usr/bin/perl 
use warnings;
use strict;

my %hash;
my @array = (1..100);

# this will be ok
$hash{\@array} = 42;

# but this will issue an error, because \@array 
# cannot be used as a key which varies
$hash{\@array}{1} = 42;

# this will be ok
$hash{1}{\@array}{1} = 42;

#this will be ok
$hash{1}{\@array}{1}{1} = 42;