Working with the original:

$n is now 101
a => 101
$n is now 102
b => 102
$n is now 103
c => 103

Data::Dumper output:

$VAR1 = {
          'c' => 103,
          'b' => 102,
          'a' => 101,
          'nextID' => sub {
                          use warnings;
                          use strict;
                          ++$n;
                          print "\$n is now $n\n";
                          return $n;
                      }
        };


Working with the original again:

$n is now 104
d => 104

Working with the re-evaluated Data::Dumper output:

Global symbol "$n" requires explicit package name at (eval 8) line 8.
Global symbol "$n" requires explicit package name at (eval 8) line 9.
Global symbol "$n" requires explicit package name at (eval 8) line 10.