use strict;
use warnings;
use Data::Dumper;
use Data::Printer;

# perl v5.22.1
# Linux 4.4.0-137-generic #163-Ubuntu SMP x86_64 x86_64 x86_64 GNU/Linux
# print $Data::Dumper::VERSION ."\n"; # v2.172
# print $Data::Printer::VERSION ."\n"; # 0.40

my $hash = {};
my $self = {};
$self->{a} = { b => $hash };
$self->{b} = $hash;
dowhile($self); # comment this line to prevent continual output
dofor($self);

sub dowhile {
  my $self = shift;

  while (my ($k, $v) = each %{$self->{a}}) {
#    print Dumper $self->{a}; # uncomment line for continual output
    p $self->{a}; # uncomment line for continual output
  }

}

sub dofor {
  my $self = shift;

  for my $k (keys %{$self->{a}}) {
    p $self->{a};
  }

}