Combining Getters and Setters

That is quite a bit of repetitive typing already, and we haven't even defined get_bar and set_bar.  Let's combine them:

    sub foo {
      my ($self, $value) = @_;
      $self->{foo} = $value if defined $value;
      return $self->{foo};
    }

Caller says:

    print $object->foo(); # Prints "new foo".
    $object->foo("my foo"); # Change foo back.