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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Conditional declarations (was: About String)
Newsgroups: comp.lang.ada
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Date: Sun, 8 Jun 2008 15:17:03 +0200
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Date: 2008-06-08T15:17:04+02:00
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On Sun, 8 Jun 2008 04:48:56 -0700 (PDT), Martin wrote:

> On 8 Jun, 08:35, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:

>> package A is
>> � � <some declarations>
>> exception
>> � � <handling elaboration problems of A, HOW?> �(:-))
>> end A;
> 
> Admittedly the range of options is pretty limited if exception
> handlers where to be added to package specs but you could log an
> indication in a package local variable, set a default or re-raise the
> exception.

Aha, so many people are looking for Ada preprocessor! (:-)) What about
catching compile error in with-ing OS.Linux in order to with OS.Windows
instead? (:-))

> I rather like the idea...that forced nesting just to catch an
> exception is quite ugly and dare I day, goes against Ada's "easy to
> read and therefore maintain" mantra...

I think it could be solved in a different way, together with a closely
related  problem:

   if X in T'Class then
      declare
         TX : T'Class renames T'Class (X);
      begin
         ...
      end;
   end if;

   if Ptr /= null then
      declare
         Ptr_All : T renames Ptr.all;
      begin
         ...
      end;
   end if;

This is a pretty frequent and quite ugly construct, especially because it
verifies the same condition twice.

I think that a fail-safe declaration is in essence a similar thing. It need
not to appear in the main declaration block, because it a combination of a
flow control and visibility scope.

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