LanX has asked for the wisdom of the Perl Monks concerning the following question:

Hi

I have to admit that most parts of Data::Dumper are rather unintuitive for me. Is there an option (or alternative modul) to display the stringified references alongside with the actual output?

So instead of

  DB<1> use Data::Dumper
 
  DB<2> $hr={a=>{b=>{c=>1}}}
 
  DB<3> print Dumper $hr
$VAR1 = {
          'a' => {
                   'b' => {
                            'c' => 1
                          }
                 }
        };
 
  DB<4> print $hr,$hr->{a},$hr->{a}{b},$hr->{a}{b}{c}
HASH(0x98a2930)HASH(0x97f5060)HASH(0x9809780)1

[download]

I'd like to get something like :

$VAR1 = {                               # HASH(0x98a2930)
          'a' => {                      # HASH(0x97f5060)  
                   'b' => {             # HASH(0x9809780)
                            'c' => 1
                          }
                 }
        };

[download]

Cheers Rolf

Replies are listed 'Best First'.
Re: Making Data::Dumper also displaying (stringified) Ref-ID's?
by toolic (Bishop) on Sep 26, 2009 at 14:27 UTC
[reply]
      Thanx toolic, indeed I have to read this thoroughly.

      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?)

      Cheers Rolf

      UDPATE: improved code example

[reply]
[d/l]
        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.

[reply]
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