CODEWITHSUNDEEP
perlhash
nowox
nowox

Reputation: 29116

How to choose which is the reference in Data::Dumper

Let's consider this example: 

#!/usr/bin/env perl
use strict;
use Data::Dumper;

my $node = node(undef, undef, 'root');
my $root = $node;

$node = node($root, $node, 'tom');
push $root->{children}, $node; 

$node = node($root, $node, 'clarence');
push $root->{children}, $node;

Data::Dumper::Purity;
#$root->{children}[0]->{younger} = $root->{children}[1];

print Dumper $root;

sub node {
    return {
        parent => shift,
        prev   => shift,
        name   => shift,
        children => [],
    };
}

Which gives this output:

$VAR1 = {
          'parent' => undef,
          'prev' => undef,
          'name' => 'root',
          'children' => [
                          {
                            'parent' => $VAR1,
                            'prev' => $VAR1,
                            'name' => 'tom',
                            'children' => []
                          },
                          {
                            'parent' => $VAR1,
                            'prev' => $VAR1->{'children'}[0],
                            'name' => 'clarence',
                            'children' => []
                          }
                        ]
        };

We can clearly see that root has 2 children named tom and clarence. The reference of clarence on tom is really clear $VAR1->{'children'}[0].

However, if I add a reference on tom to clarence with $root->{children}[0]->{younger} = $root->{children}[1];, the output get messed up: 

$VAR1 = {
          'parent' => undef,
          'prev' => undef,
          'name' => 'root',
          'children' => [
                          {
                            'parent' => $VAR1,
                            'prev' => $VAR1,
                            'younger' => {
                                           'parent' => $VAR1,
                                           'prev' => $VAR1->{'children'}[0],
                                           'name' => 'clarence',
                                           'children' => []
                                         },
                            'name' => 'tom',
                            'children' => []
                          },
                          $VAR1->{'children'}[0]{'younger'}
                        ]
        };

Is there any possibility to constraint Data::Dumper or any other dumper to always consider some keys as references in order to properly display a tree?

Upvotes: 1

Views: 70

Answers (1)

Borodin
Borodin

Reputation: 126742

There isn't a lot you can do because Data::Dumper scans structures depth-first, but I suggest that you use

$Data::Dumper::Deepcopy = 1

which will duplicate hash values in the output instead of inserting cross-references. This is the result

$VAR1 = {
          'prev' => undef,
          'children' => [
                          {
                            'parent' => $VAR1,
                            'name' => 'tom',
                            'younger' => {
                                           'children' => [],
                                           'prev' => $VAR1->{'children'}[0],
                                           'name' => 'clarence',
                                           'parent' => $VAR1
                                         },
                            'prev' => $VAR1,
                            'children' => []
                          },
                          {
                            'children' => [],
                            'prev' => {
                                        'parent' => $VAR1,
                                        'name' => 'tom',
                                        'younger' => $VAR1->{'children'}[1],
                                        'prev' => $VAR1,
                                        'children' => []
                                      },
                            'name' => 'clarence',
                            'parent' => $VAR1
                          }
                        ],
          'parent' => undef,
          'name' => 'root'
        };

Upvotes: 1

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