package Duck::Secret;

use Class::InsideOut qw( private id register );

private secret => my %SECRET;

sub new { 
  my $self = register( bless \(my $s), shift );
  $SECRET{ id $self } = int( rand(100) );
  return $self;
}

sub guess_secret {
  my ($self, $guess) = @_;

  return $guess == $SECRET{ id $self };
}

##</code><code>##

# continuing previous code example

sub secret {
  my $self = shift;
  die "Secret is a protected field" if ! caller(0)->isa( __PACKAGE__ );
  $SECRET{ id $self } = shift if @_;
  return $SECRET{ id $self };
}