From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,f2690a5e963b61b6
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!postnews.google.com!g44g2000cwa.googlegroups.com!not-for-mail
From: "Matthew Heaney" <mheaney@on2.com>
Newsgroups: comp.lang.ada
Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
Date: 5 Jul 2005 07:51:17 -0700
Organization: http://groups.google.com
Message-ID: <1120575076.876798.108220@g44g2000cwa.googlegroups.com>
References: <1120474891.635131.216700@g44g2000cwa.googlegroups.com>
NNTP-Posting-Host: 66.162.65.162
Mime-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
X-Trace: posting.google.com 1120575082 9683 127.0.0.1 (5 Jul 2005 14:51:22
 GMT)
X-Complaints-To: groups-abuse@google.com
NNTP-Posting-Date: Tue, 5 Jul 2005 14:51:22 +0000 (UTC)
In-Reply-To: <1120474891.635131.216700@g44g2000cwa.googlegroups.com>
User-Agent: G2/0.2
Complaints-To: groups-abuse@google.com
Injection-Info: g44g2000cwa.googlegroups.com; posting-host=66.162.65.162;
   posting-account=Zl1UPAwAAADEsUSm1PMMiDjihtBlZUi_
Xref: g2news1.google.com comp.lang.ada:11865
Date: 2005-07-05T07:51:17-07:00
List-Id: <comp.lang.ada>



Dmitriy Anisimkov wrote:
> begin
>    Table.Insert (Container, "one", 11111, Cursor, Success);
>    pragma Assert (Success);
>    Table.Insert (Container, "two", 22222, Cursor, Success);
>    pragma Assert (Success);
>    Table.Insert (Container, "three", 33333, Cursor, Success);
>    pragma Assert (Success);

You don't need conditional insertion here.  Just use the 3-param
Insert:

  Container.Insert ("one", 1);
  Container.Insert ("two", 2);
  Container.Insert ("three", 3);


>    Table.Insert (Container, "two", 2222, Cursor, Success);
>    pragma Assert (not Success);
>
>    --  Delete element "two" independently.
>
>    Cursor2 := Table.Find (Container, "two");
>    Table.Delete (Container, Cursor2);
>
>    --  The erroreneous line below do nothing and do not raise any
> exception.
>
>    Table.Replace_Element (Cursor, -22222);

Well of course this is erroneous, since the element designated by
Cursor was deleted in the previous statement!


> ------------------------------------------------------------
> The code above have to raise at least runtime error at
> Table.Replace_Element (Cursor, -22222); but it do nothing and do not
> raise any exception.

It certainly does not have to raise a runtime error.  It can do
anything it likes, since the behavior is undefined.


> valgrind showing the memory corruption

That's good, since what you did corrupts the memory.


> ADT do not have a cursors at all. All get/put operations from container
> is just per key. All iterations via the containers are with simple
> generic procedures.

This is like saying, Tall buildings shouldn't have windows, since if
there's a window, you might jump out of the window and hurt yourself.

The solution is simple: don't jump out of windows...


> I'm not sure that it is possible to implement runtime error detection
> in such cursor situation.

It's software, we can doing anything we want.  So of course you can
detect dangling cursors -- but not without a runtime penalty (in both
time and space).


> I think that ADT is much more on the Ada way then proposed
> Ada.Containers with cursors.

If you don't like cursors, then don't use 'em.  Certainly with a map,
you never need to use cursors.