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: 103376,7d3cb5920e882220
X-Google-Attributes: gid103376,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news4.google.com!feeder1-2.proxad.net!proxad.net!feeder1-1.proxad.net!club-internet.fr!feedme-small.clubint.net!nuzba.szn.dk!news.jacob-sparre.dk!pnx.dk!not-for-mail
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Exceptions
Date: Mon, 10 Dec 2007 20:12:03 -0600
Organization: Jacob's private Usenet server
Message-ID: <fjkres$t27$1@jacob-sparre.dk>
References: 
 <5947aa62-2547-4fbb-bc46-1111b4a0dcc9@x69g2000hsx.googlegroups.com>
 <bfea7c31-a6d8-420c-8ba3-8a2df7749253@s19g2000prg.googlegroups.com>
 <m2k5nqib4y.fsf@mac.com> <wccsl2b1r0j.fsf@shell01.TheWorld.com>
 <475c6ed8$0$13111$9b4e6d93@newsspool2.arcor-online.net>
 <1kxk3hlfa25dw$.fl2wvbn0tpbg$.dlg@40tude.net>
NNTP-Posting-Host: static-69-95-181-76.mad.choiceone.net
X-Trace: jacob-sparre.dk 1197338909 29767 69.95.181.76 (11 Dec 2007 02:08:29
 GMT)
X-Complaints-To: news@jacob-sparre.dk
NNTP-Posting-Date: Tue, 11 Dec 2007 02:08:29 +0000 (UTC)
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.2800.1914
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1914
Xref: g2news1.google.com comp.lang.ada:18885
Date: 2007-12-10T20:12:03-06:00
List-Id: <comp.lang.ada>

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:1kxk3hlfa25dw$.fl2wvbn0tpbg$.dlg@40tude.net...
...
> 1. How often do you declare a new exception when writing a new subprogram?
> My guess is about 1 / 10_000.

For me, it is more like 1/100. Most subsystems get their own set of
exceptions.

> 2. How often does a caller "eat" an exception of the callee instead of
> propagating it further? My guess is 1 / 10.

This I agree with, and it is my primary objection to exception contracts.
This means that you'll have to write long-winded handlers and/or contracts
on 9/10 of the calls. That is, it is the common case that takes more work.
That's usually bad.

> There is not that many handlers in a good designed code. This is probably
> the reason why people forget to handle exceptions properly. They are not
> that visible.

That's true: a lot of systems that I write have no handlers at all because
any exception being raised is a bug, and I want to know. The biggest problem
is insuring enough test coverage to make sure that the (latent) exceptions
(that is, bugs) get raised.

Most of the handlers I do write are of the form:
    begin
          Open (...); -- File or socket or ...
    exception
          when others => -- Couldn't open whatever. Abort program or
process.
    end;
    -- Use the open file.

But I'm not usually writing safety-critical systems. For programs that need
to keep running (for example, a  mail server), I use a single global others
handler that logs any exceptions, since there should be none. But there
would no way to prove that statically, and I don't think I'd want to have to
write code structured to be able to try.

                                Randy.