package Bar;
use base 'Foo';
use fields qw(baz _Bar_private);        # not shared with Foo
sub new {
  my $class = shift;
  my $self = fields::new($class);
  $self->SUPER::new();                # init base fields
  $self->{baz} = 10;                  # init own fields
  $self->{_Bar_private} = "this is Bar's secret";
  return $self;
}