Not an especially useful technique for managing inside-out objects. (Not without some care anyway.) Reference addresses can be recycled.

use strict;
use warnings;
use Scalar::Util 'refaddr';
use Data::Dumper;

for my $i (0..2)
{
    my $hash = [$i];
    
    printf "The hash has refaddr %08X, and contents are...\n", refaddr
+($hash);
    print Data::Dumper->Dump([$hash], ['$hash']);
}
[download]

With carefully written CLONE and DESTROY methods, using the refaddr as a hash key can be made to work, but something like Hash::FieldHash saves a lot of work.