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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Forcing Exception Handling
Newsgroups: comp.lang.ada
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Date: Tue, 1 Mar 2011 09:56:48 +0100
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Date: 2011-03-01T09:56:48+01:00
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On Mon, 28 Feb 2011 16:19:22 -0800 (PST), Shark8 wrote:

> In fact, given that Ada doesn't have an "exception hierarchy" like
> Delphi does it may be a horrendous idea: There is no way to catch all
> exceptions because there is no way to catch a  all exceptions of a
> certain type (i.e. Storage_Error'Class) which is caused by the lack of
> some root-type "Exception_Root."

It is a question. Since exceptions are used in case-like clauses, more
natural where a model of a discrete type. In order to have constructs like:

   when Numeric_Exception'First..Numeric_Exception'Last =>

BTW, it shows the importance of extensible enumeration types, because
exceptions should be that kind of type.

When exceptions are bunch of types like in C++ you would loose the above.

Also consider this:

   declare
      Foo : exception:
   begin
      ...
      raise Foo;
   end;  -- Foo propagates out its scope!!

Unless Ada would have upward closures, that cannot work when Foo is a type.
I hope everybody agrees that upward closures should not be introduced.

A possibility to handle this is exception promotion, e.g. Foo to
Program_Error, when Foo gets finalized.

BTW, contracted exception would solve this problem by making such programs
illegal: each block would have an implicit contract not to propagate local
exceptions.

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