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From: Stefan Bellon <bellon@software-erosion.org>
Newsgroups: comp.lang.ada
Subject: Re: Generic Zero Length Array
Date: Fri, 22 Feb 2008 16:22:24 +0100
Organization: Comp.Center (RUS), U of Stuttgart, FRG
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Date: 2008-02-22T16:22:24+01:00
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On Fr, 22 Feb, shaunpatterson@gmail.com wrote:

> if Error_Condition then
>   declare
>     type Result is new Element_List (Indexing.First + 1 ..
> Indexing'First);
>     Result_String : Result;
>   begin
>      return Element_List (Result);
>   end;
> end if;
> 
> How do I initialize this array when I can't know what type it is or
> will be?

Funny, just yesterday I came across the code that did exactly this
in our software:

   if List_Length = 0 then
      if Index_Type'Base'First = Index_Type'Base'Last then
         --  there seems to be no way to declare a null array
         --  for a `type Index_Type is (A)`
         raise Constraint_Error;
      else
         --  Workaround due to GNAT 6.0.2 bug (H221-018).
         return (Index_Type'Base'Last ..
                 Index_Type'Base'Pred (Index_Type'Base'Last) => <>);
      end if;
   else
      --  non-empty case
   end if;

And previously we had

         return (Index_Type'Base'Last .. Index_Type'Base'First => <>);

written, which triggered H221-018, therefore we rewrote to use 'Pred.

Greetings,
Stefan

-- 
Stefan Bellon