You NEED to use the extended version of the dumper to do self referencing dump.
#!perl -w
use Data::Dumper;
$Data::Dumper::Purity=1;
$a = { type => 'int' };
$b = \$a->{type};
print "case 1\n", Data::Dumper->Dump([$a, $b], [qw/a b/]);
print "case 2\n", Data::Dumper->Dump([$a, $b], [qw/x y/]);
print "case 3\n", Data::Dumper->Dump([$b, $a], [qw/b a/]);
print "case 4\n", Data::Dumper->Dump([$b, $a]);

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This gives you the following output:
case 1
$a = {
       'type' => 'int'
     };
$b = \$a->{'type'};
case 2
$x = {
       'type' => 'int'
     };
$y = \$x->{'type'};
case 3
$b = \'int';
$a = {
       'type' => ${$b}
     };
case 4
$VAR1 = \'int';
$VAR2 = {
          'type' => ${$VAR1}
        };

[download]
In other words, Data::Dumper is smart, but not 'that' smart. In case of dumping variables referencing each other, you have to use the extended Dump and optionally give it the names of your variables so it can distinguish them properly.

Case 3 and 4 are special, they do not match exactly the original input variables. This is caused by the Data::Dumper's parser. The parser maintains a symbolic table of all variables seen, and for every new variable, it will search in the table first. If a match was found, then it would interpret the new variable based on the matching variable in the table. Therefore the ordering of the variables is important, just like defining them in perl script.

In reply to Re: Data::Dumper scalar refs undef by Roger
in thread Data::Dumper scalar refs undef by bsb

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