sub factory {
      my $self = shift;
      ...
      my $newInstance = new Bar(...);
      ...
      return $newInstance;
  }

##</code><code>##

  sub factory {
      my $self = shift;
      ...
      my newInstance = $self->factoryClass()->new(...);
      ...
      return newInstance;
  }

  sub factoryClass {
      "Bar"
  }