Re: Entity and Identity

On Jul 28, 2:39 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> Nilone wrote:
> > On Jul 28, 1:21 am, rp_at_raampje.(none) (Reinier Post) wrote:
>
> >>Nilone wrote:
>
> >>>On Jul 25, 10:34 am, Nilone <rea..._at_gmail.com> 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.

Nah, that doesn't suit me. Received on Tue Jul 28 2009 - 15:04:05 CEST