I was actually looking for a way to display the difference between deep and flat copy to a newbie, and no figured out that the Seen-Mechanism in Data::Dumper already reveals it, without the need to print the Ref-IDs. 8)

  DB<90> $hr2={%$hr1}  # shallow copy
 
  DB<91>  print Data::Dumper->Dump([$hr1,$hr2],[qw/hr1 hr2/])
$hr1 = {
         'a' => {
                  'b' => {
                           'c' => 1
                         }
                }
       };
$hr2 = {
         'a' => $hr1->{'a'}
       };
 
  DB<92> x $hr1,$hr2
0  HASH(0x8b64b78)
   'a' => HASH(0x8b64c18)
      'b' => HASH(0x8af9120)
         'c' => 1
1  HASH(0x8b156c0)
   'a' => HASH(0x8b64c18)
      -> REUSED_ADDRESS
[download]

Anyway IMHO an option to add the IDs as comments would be welcomed by many people as a valuable feature!

(update: maybe this can be done with Data::Dump::Streamer?)

UDPATE: improved code example

Dump the original and the copy using one call to Dumper, and the difference between a shallow and a deep copy will be obvious.

use Storable     qw( dclone );
use Data::Dumper qw( Dumper );

my %hash = (a=>{b=>{c=>1}});

my %shallow = %hash;
my %deep    = %{ dclone(\%hash) };

local $Data::Dumper::Indent = 1;

print("Shallow\n");
print("-------\n");
print(Dumper(\%hash, \%shallow));

print("\n\n");

print("Deep\n");
print("----\n");
print(Dumper(\%hash, \%deep));
[download]

Shallow
-------
$VAR1 = {
  'a' => {
    'b' => {
      'c' => 1
    }
  }
};
$VAR2 = {
  'a' => $VAR1->{'a'}
};


Deep
----
$VAR1 = {
  'a' => {
    'b' => {
      'c' => 1
    }
  }
};
$VAR2 = {
  'a' => {
    'b' => {
      'c' => 1
    }
  }
};
[download]

As you can see, the shallow copy clearly references back to the original, whereas the deep copy doesn't.

Thx, but what's the difference to the code in the post you're replying to?

IMHO it's essentially the same code!(?)

Cheers Rolf