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-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,1e4bb63e08046e1a
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2002-10-25 08:06:12 PST
Newsgroups: comp.lang.ada
Path: 
 archiver1.google.com!news1.google.com!newsfeed.stanford.edu!canoe.uoregon.edu!logbridge.uoregon.edu!uunet!sea.uu.net!sac.uu.net!ash.uu.net!world!news
From: Robert A Duff <bobduff@shell01.TheWorld.com>
Subject: Re: is exception when others => null; smart?
User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2
Sender: news@world.std.com (Mr Usenet Himself)
Message-ID: <wcclm4mk19r.fsf@shell01.TheWorld.com>
Date: Fri, 25 Oct 2002 15:04:48 GMT
Content-Type: text/plain; charset=us-ascii
References: <slrnarfvcc.4ud.randhol+news@kiuk0152.chembio.ntnu.no>
 <tBTt9.1279$13.184@news1.bredband.com>
NNTP-Posting-Host: shell01.theworld.com
Mime-Version: 1.0
Organization: The World Public Access UNIX, Brookline, MA
Xref: archiver1.google.com comp.lang.ada:30133
Date: 2002-10-25T15:04:48+00:00
List-Id: <comp.lang.ada>

"Per Sandbergs" <prsa@cntw.com> writes:

> 1)
>   main_loop:
>     loop
>       begin
>         lots of operations.
>       exception
>         when others =>
>           report the error and reset top a safe state in order to continue.
>     end loop;
> 
> 2)
> function work_is_ok(fool) return boolean is
> begin
>     some computations
> exception --
>     when others =>
>         return false; -- or report error and eventualt raise.
> end;
> 2)
> procedure must_not_raie(fool) is
> begin
>     some computations
> exception
>     when others =>
>         null;
> end;
> So when others => null is only to be used when you are expecting the
> unexpected.
> I wont be supprised if other peoplen are of different opinion but after
> integration a number of large systems i find the above aproach "wise".

Also,

4)

    when others =>
        clean up;
        raise;

As in:

    procedure Walk_Tree(...) is
    begin
        Push current node on stack;
        walk subtrees;
        Pop stack;
    exception
        when others =>
            Pop stack; -- Keep stack in synch even in case of exception.
            raise;
    end Walk_Tree;

Finalization can also be used for this purpose, and that's a cleaner way
to do it, but finalization is *very* expensive in most Ada compilers,
whereas the above "when others" is pretty cheap.

- Bob