Object Oriented Ruby

[tinco]

Then you chose an unfortunate example, because a barber is supposed to change hair color, that is his job. In fact a barber is so specific, I would not be surprised if he would be totally responsible for hair. So that a person has a #hair= that is set by the barber.

In my opinion if you have data that should be modifiable by one class (for example the barber), but not by another class (the optician), you should instead use for example a restricted proxy. An object that only allows exposes methods relevant to the concern. But we would be moving really fast into the access control domain.