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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Class wide preconditions: error in GNAT implementation?
Date: Mon, 18 Feb 2013 20:44:10 +0100
Organization: cbb software GmbH
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Date: 2013-02-18T20:44:10+01:00
List-Id: <comp.lang.ada>

On Mon, 18 Feb 2013 11:02:31 -0800 (PST), ytomino wrote:

> On Monday, February 18, 2013 5:30:16 PM UTC+9, Dmitry A. Kazakov wrote:
>> No, all preconditions must be satisfied, otherwise, the program is
>> incorrect, provided it is correctness we are talking about.
>> 
>> But then the precondition of B'Class is *required* to be true for an object
>> which is in that class. The precondition of A'Class is weaker and need not
>> to be checked if one for B'Class is satisfied.
> 
> Excuse me for misunderstanding your opinion.
> 
> But, do you have the same mistake as mine in�the first post?
> Preconditions are combined by "or else".

That depends on what you do with the set of values at hand and what the
terms being combined mean. If you narrow the set, then obviously the
precondition strengthens which could mean "and" for the terms associated
with independent subsets of values. If you widen the set it could be "or."
It could be anything in more complex cases when subsets are not independent
or when some values are added and some are removed, when some operations
are in, some are out and some are inout. etc.

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