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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Generic-Package Elaboration Question / Possible GNAT Bug.
Date: Wed, 23 Nov 2011 10:05:14 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2011-11-23T10:05:14-05:00
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"Yannick Duch�ne (Hibou57)" <yannick_duchene@yahoo.fr> writes:

> Le Mon, 21 Nov 2011 14:08:04 +0100, Robert A Duff
> <bobduff@shell01.theworld.com> a �crit:
>> And there are a few cases where we
>> deliberately "cheat" in the RM, by making something raise an exception
>> in a generic, when it would normally be a legality rule.

> Please, an example! :)

In 4.6:

39.1/2    * {AI95-00392-01} If the component types of the array types are
            anonymous access types, then a check is made that the
            accessibility level of the operand type is not deeper than that of
            the target type.

[Program_Error is raised at run time if this check fails.]

39.b/2      Reason: This check is needed for operands that are access
            parameters and in instance bodies. Other cases are handled by the
            legality rule given previously.

If there are no access parameters involved, most implementations will
check this rule at compile time of the instance, and give a warning.
The only reason it needs to be a run-time check is to avoid breaking
the contract model (ignoring the access parameter case), which is
sort of a "cheat".

- Bob