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Newsgroups: comp.lang.ada
Subject: Re: Exceptions
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From: Stephen Leake <stephen_leake@stephe-leake.org>
Date: Sun, 09 Dec 2007 05:24:51 -0500
Message-ID: <uk5nob1xo.fsf@stephe-leake.org>
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Date: 2007-12-09T05:24:51-05:00
List-Id: <comp.lang.ada>

"Peter C. Chapin" <pchapin@sover.net> writes:

> Dmitry A. Kazakov wrote:
>
>> The problem here is not exception contracts but firstly lack of subtypes in
>> C++. Ada has subtypes, so the code above could be rewritten [properly]:
>> 
>> if X in Safe_For_P1 then
>>    declare
>>       Checked_X : Safe_For_P1 renames X;
>>    begin
>>       P1 (Checked_X); -- This does not raise exception
>
> Here is my example again:
>
> if Has_Acceptable_Value(X) then
>   P1(X);
> end if;
>
> What if Has_Acceptable_Value(X) returns true if X is prime... or a
> positive power of two? I don't believe you can use Ada subtypes to
> express conditions like that---or indeed many other possibilities.

Right. You have to use SPARK Ada. 

-- 
-- Stephe