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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada Successor Language
Date: Tue, 26 Jun 2018 19:42:45 +0200
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Xref: reader02.eternal-september.org comp.lang.ada:53337
Date: 2018-06-26T19:42:45+02:00
List-Id: <comp.lang.ada>

On 2018-06-26 19:20, Shark8 wrote:
> On Monday, June 25, 2018 at 2:20:42 AM UTC-6, Marius Amado-Alves wrote:
>> This conjecture, that OO polymorphism is *always* preferrable to generics, is picking my mind big time. I've got a strong intuition that there are cases best served by generics. I'll try to find examples. Or if anyone has some please post.
> 
> I disagree with that summation wholeheartedly; one place generics are superior to OO is in sharing code. OOP is _not_ good for that purpose, despite some claims it is.

How so? The code of the bodies of inherited primitive operations and the 
bodies of class-wide operations are shared the in proper sense of this word.

Sharing with generics is a quite difficult task if you really tried to 
do this. E.g. there are several approaches to specialization of shared 
generic code:

1. You can pass a package instance

    generic
       type T is ...
       package Foobar is new Foo (T => T, ...
    package Bar

2. You can use child generic package

    generic
       ...
    package Foo.Bar is

None of which works satisfactory and geometrically explodes in presence 
of several type-parameters. An equivalent of

    Bar (X : A'Class; Y : B'Class; Z : C'Class);

is barely possible.

P.S. I have an impression that people advocating generics never really 
used them beyond instantiation of containers from the standard library. 
A real-life challenge looks like this:

    http://www.dmitry-kazakov.de/ada/fuzzy.htm#8

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de