Partial Inheritance

Suppose the Employee class is also keeping track of employee names
The ->name method will maintain a hash of all names:

        my %names;

        sub name {
          my $self = shift;
          my $old_name = $self->{NAME};
          if (@_) {
            my $new_name = shift;
            $names{$old_name}-- if defined $old_name;
            $names{$new_name}++;
            $self->{NAME} = $new_name;
          }
          $self->{NAME};
        }

This overrides Person::name
If Person::name is very complicated, we will have to duplicate its behavior
(For example, if Person::name is backing the names in a database)
If someone changes Person::name, the new behavior will not be reflected here