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From: "Matthew Heaney" <mheaney@on2.com>
Newsgroups: comp.lang.ada
Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
Date: 5 Jul 2005 08:01:47 -0700
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Date: 2005-07-05T08:01:47-07:00
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Dmitriy Anisimkov wrote:
> ----------------------------
> Table.Insert (Container, "two", 2222, Cursor, Success);
>
> if not Success then
>    Some_Package.Delete_From_Container (Key => "two");
> end if;
>
> Table.Replace_Element (Cursor, -22222);
> --------------------

This is confused.  No matter what value is returned for Success (BTW:
the formal parameter is named "Inserted"), the key "two" is in the map.
 So the predicate that follows the Insert is not necessary.

As has already been pointed out, the call to Replace_Element is
erroneous, since the element designated by Cursor was deleted (at least
that's what I think the example is doing).

The solution to the problem is to simply not use cursors:

Container.Include ("two", 2222);
...
Container.Include ("two", -22222);

Now all is well.  Just use Include, and you won't have any problems.
Alternatively, you can say:

Container.Include ("two", 2222);
...
declare
   C : Cursor;
   B : Boolean;
begin
   Container.Insert ("two", -22222, C, B);
   if not B then
      Replace_Element (C, By => -22222);
   end if;
end;

You really need to sit down and read the AI:

<http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-20302.TXT?rev=1.21>

-Matt