I just found this message (because Mike posted the tinyurl....) and couldn't resist responding...
"Zsiros Levente" <[EMAIL PROTECTED]> wrote > If we're talking about data hiding, let me ask: why Python doesn't > implement data hiding (I mean 'private' and 'protected')? I consider > it > a very important OOP feature, because that makes OOP different from > structural programming. This is a hot-button of mine... Why do you think data hiding is important for OOP? And in particular why do you think it differentiates OOP from structural techniques? Data Hiding was not part of the early OOP languages (Simula, Lisp and the first Smalltalks) it was introduced first by Smalltalk in (Smalltalk 74 I think) and it was only when C++ came out that all the public/private nonsense appeared, followed by protected in C++ v2.0 Many OOP languages do not support data hiding, it is not necessary for OOP. Data hiding is supported in many structual languages like the Modula family and ADA., but they are not OOP. (The concept was introduced by David Parnas in 1972 - long before OOP became popular) The point being that Data hiding is an orthogonal issue to OOP which relies on encapsulation and polymorphism. - Encapsulation(*) is the ability to treat the data and methods as a single entity - an object. - Polymorphism is the ability for different objects supporting the same protocol to react in different ways to the same message. Inheritance is an optional extra but is usually required to implement polymorphism... (*)Some texts get data hiding and encapsulation confused. Encapsulation as originally applied to OOP is about joining the data and function together - so fundamental to OOP that some folks forget its even there as a feature! Data hiding is about making data available through an API. That API could be an object's protocol or it could be a module interface. It's usually a good thing to do, but not a requirement of OOP. Rant over, If anyone wants a more academic review oif the differences between data hiding (or more correctly, information hiding), encapsulation and abstraction see this white paper: http://www.itmweb.com/essay550.htm by Ed Berard. -- Alan Gauld Author of the Learn to Program web site http://www.freenetpages.co.uk/hp/alan.gauld _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
