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From: Maciej Sobczak <no.spam@no.spam.com>
Newsgroups: comp.lang.ada
Subject: Re: Structured exception information
Date: Tue, 16 Jan 2007 15:44:43 +0100
Organization: CERN News
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Date: 2007-01-16T15:44:43+01:00
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Dmitry A. Kazakov wrote:

>>>    procedure Foo raises Some_Error'Class;
>>>
>>> should be illegal.
>> Why?
> 
> Because otherwise you could raise a type from the class, of which scope is
> narrower than one of the handler.

Then I would expect slicing to the type that the handler sees.
Which brings another point - the handler has to *see* the type it wants 
to handle, which means that the type in question cannot have narrower 
scope anyway and even if it has, the handler will not be able to misuse it.

>    when E : Some_Error'Class =>
>    when E : Some_Error  =>
> 
> We definitely do not want whens to become ordered.

You have them ordered already, just not in a sequence, but across all 
enclosing scopes (handlers are searched from "inside" to "outside", so 
they might as well be traversed from top to down in addition). I don't 
see much difference.

> Even less, to have
> contracts which cannot be checked.

You can check it. Java guys did it, so there is a prior art. :-)


-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/