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From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Is this expected behavior or not
Date: Fri, 12 Apr 2013 10:00:26 -0700
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Xref: news.eternal-september.org comp.lang.ada:14974
Date: 2013-04-12T10:00:26-07:00
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On 04/12/2013 02:09 AM, J-P. Rosen wrote:
>
> I just said that the commonly accepted meaning of inheritence is
> specialization, where the upper level classes are more general and the
> lower ones are more specialized. I agree that inheritance has its own
> problems - that's why I use it rarely, I prefer composition.

While it's true that many proponents of type extension claim they're creating 
specialization classifications, starting with general classes and extending them 
to create more specialized ones, it's also demonstrably wrong in most cases: 
It's a rare specialization classification in which the more specialized classes 
need more data than the more general ones. In classifying plane figures, for 
example, the general classes (such as "polygon") clearly need more data in their 
representations than the specialized classes (such as "square").

Type extension starts with abstract classes, and extends them to create more 
concrete ones, a fact that Ada recognizes with its "abstract" reserved word.

-- 
Jeff Carter
"Why, the Mayflower was full of Fireflies, and a few
horseflies, too. The Fireflies were on the upper deck,
and the horseflies were on the Fireflies."
Duck Soup
95