Re: Entity and Identity

From: Bob Badour <>
Date: Tue, 28 Jul 2009 09:39:33 -0300
Message-ID: <4a6ef186$0$23777$>

Nilone wrote:

> On Jul 28, 1:21 am, rp_at_raampje.(none) (Reinier Post) wrote:

>>Nilone wrote:
>>>On Jul 25, 10:34 am, Nilone <> wrote:
>>>>OO classes are used to create data types, since encapsulation,
>>>>constructors and attributes are necessary features to create data
>>>>types. However, it fails as a type system since it allows subtypes to
>>>>be defined that breaks the original type. It also allows for the
>>>>creation of reference types, which is an oxymoron.
>>>I mean mutable types, not reference types.
>>Aren't those problems caused by the use of mutability
>>rather than OO inheritance? Of course subtypes can break
>>the original type, but developers aren't supposed to do that.
>>What alternative to inheritance do you propose for sharing
>>function implementations across objects of different but related types,
>>and how is it any safer?
> Types define values.  Values aren't mutable, since mutability implies
> a persistent identity beyond the value itself.  As soon as you have
> mutability, you have a state machine, and subtyping state machines is
> a problem.  Subtyping an interface and creating a new state machine
> for it is fine.

Forget state machines. As soon as you have mutability, you have a variable. Leave it at that. Received on Tue Jul 28 2009 - 14:39:33 CEST

Original text of this message