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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada requires too much typing!
Newsgroups: comp.lang.ada
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Date: Fri, 28 May 2010 21:39:28 +0200
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Date: 2010-05-28T21:39:22+02:00
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On Fri, 28 May 2010 21:05:00 +0200, Georg Bauhaus wrote:

> On 28.05.10 19:31, Dmitry A. Kazakov wrote:
>> On Fri, 28 May 2010 11:52:09 -0400, John B. Matthews wrote:
>> 
>>> In Java, the presence of a suitable handler for checked exceptions is 
>>> enforced at compile-time:
>>>
>>> <http://java.sun.com/docs/books/jls/third_edition/html/exceptions.html#11.2>
>>>
>>> The feature may be regarded as controversial:
>>>
>>> <http://java.sun.com/docs/books/tutorial/essential/exceptions/runtime.html>
>> 
>> BTW, this is the same issue as with Eiffel's "contracts" and Ada's
>> assertions. The problem is misuse of exceptions:
>> 
>> 1. IF the exception is a part of the contracts <=> the client is supposed
>> to handle it, THEN it must be checked.
>> 
>> 2. IF no client can handle it, THEN it shall not be, the program must
>> rather abort itself or break into the debugger. 
> 
> 2. is what Eiffel programs do, but the compiler does not check
> the presence of exception handlers for postconditions that
> may fail (and thus raise an exception).  If it did, will it not
> mean exception handlers pretty much everywhere?

No. Exceptions are supposed to propagate. A propagating exception is
unhandled one.

If you confuse 1 and 2 you get troubles. Another example from Ada is
Program_Error, e.g. from Initialize/Finalize/Adjust. It is meaningless and
very harmful. If you are in 2, it is too LATE to raise anything.

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