Thank you for pointing out inheritance merlyn!
I saw something like this a few weeks ago... wish I remembered where exactly.

package Class_A;

sub new {

  ## the usual:
  my $class = shift;
  my $self = {};  
  bless $self, $class;
}

sub newB {
  
  my $self = {};  
  bless $self, 'Class_B';
}
[download]

Does this ring any bells?