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From: Cyrille <comar@eu.adacore.com>
Newsgroups: comp.lang.ada
Subject: Re: Preventing type extensions
Date: Tue, 21 Sep 2010 06:57:36 -0700 (PDT)
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Date: 2010-09-21T06:57:36-07:00
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On Sep 13, 11:13=A0pm, "J-P. Rosen" <ro...@adalog.fr> wrote:

> These arguments make sense for languages without the notion of
> class-wide types.

all OO languages I'm aware of, have the notion of classwide types...
They just don't make the distinction between a type on its own and a
type with its derived types. If you think about it, it is a peculiar
distinction at the "design" level. A horse is an animal... When I deal
with animals, I must be ready to accept that maybe the animal I'm
dealing with may be a horse, or may be something else. It's peculiar
to expect it to be the pure notion of "animal" and nothing else...

> However, I think that redispatching can be replaced
> with class-wide operations, with great benefits from the POV of testing.

In some cases, it may be true. Generally speaking, it is an important
to distinguish between primitive operrations and class wide
operations. They both have their use. If you are suggesting the rule
"any primitive operation that calls another primitive op of the same
type (that usually is when redispatch should occur) must be
transformed into a class-wide operation", I'm afraid this is a fierce
restriction... much fiercer than the simple dispatch rule... which
imposes one particular style of programming.

> Cyril, will you come to the workshop? That would be very valuable.

No, I don't plan to go. Note that on our side, we are already working
on our own set of recommendations... maybe we should try to find a
vehicle more permanent than a conference to make a community effort on
this...