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From: "Nick Roberts" <nickroberts@adaos.worldonline.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: Overridability of _private_ predefined "="  [was Re: list
 strawman]
Date: Sat, 19 Jan 2002 22:42:29 -0000
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Date: 2002-01-19T22:42:29+00:00
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"Vincent Marciante" <marciant_remove@li.net> wrote in message
news:3C49A5C4.51D6@li.net...

> ...
> This is why I find the situation to be so bad now.  A generic written
> for Ada 83 that only imports a private type can not be made into a valid
> Ada 95 one by simply transforming its spec by adding the importation of
> "=" for that type;  Its body must also be analyzed and possibly changed
> so as to use componant by componant comparison for any composite types
> having the private type as a componant (or predefined "=" has to be
> overridden for those composite types _and_ any other composite types the
> have those composite types as componants.)
>
> What was impossible (?) to do wrong in Ada 83 has now become a pitfall
> in Ada 95. were by we have to dilligently follow the verbal guideline
> that you just suggested.

AI-123 discusses this in some detail, and results (rev 12) in a corrigendum
which specifically compels language-defined types to be composable with
respect to equality (thus forcing them to be implemented either without
redefined equality or as tagged types). I smell a hint of hypocrisy here.

Personally, I completely agree with Vincent. Damn Ada 83 compatibility, and
damn implementation complexities: equality should always be composable; the
current state is plainly a potential source of 'nasty surprises'; the
language is purportedly supposed to avoid nasty surprises. But I am a small
voice.

--
Best wishes,
Nick Roberts