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: 103376,6b1a1ed8b075945
X-Google-Attributes: gid103376,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Newsgroups: comp.lang.ada
Subject: Re: Allocators and exceptions
References: <1189323618.588340.87180@o80g2000hse.googlegroups.com>
 <jvREi.80243$ax1.52638@bgtnsc05-news.ops.worldnet.att.net>
 <1189369871.672082.162750@50g2000hsm.googlegroups.com>
 <kv25hx961chk.5kg3us0ye06y.dlg@40tude.net>
 <1189460936.295604.143720@r29g2000hsg.googlegroups.com>
 <ixr8l1ty6phe$.stdgh66rlsrl$.dlg@40tude.net>
 <1189502377.626510.172690@22g2000hsm.googlegroups.com>
 <utzq0kqy3.fsf@stephe-leake.org>
From: Markus E L
 <development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de>
Date: Wed, 12 Sep 2007 16:14:23 +0200
Message-ID: <o04pi0q8cg.fsf@hod.lan.m-e-leypold.de>
User-Agent: Some cool user agent (SCUG)
Cancel-Lock: sha1:l7308uulW0Her+9ksVEfgGvCgEQ=
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
NNTP-Posting-Host: 88.74.57.86
X-Trace: news.arcor-ip.de 1189606188 88.74.57.86 (12 Sep 2007 16:09:48 +0200)
X-Complaints-To: abuse@arcor-ip.de
Path: 
 g2news2.google.com!news3.google.com!feeder3.cambrium.nl!feed.tweaknews.nl!newsfeed.kamp.net!newsfeed.kamp.net!news.unit0.net!newsfeed.arcor-ip.de!news.arcor-ip.de!not-for-mail
Xref: g2news2.google.com comp.lang.ada:1920
Date: 2007-09-12T16:14:23+02:00
List-Id: <comp.lang.ada>


Stephen Leake wrote:

> Maciej Sobczak <see.my.homepage@gmail.com> writes:
>
>> On 11 Wrz, 11:16, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
>> wrote:
>>
>>> >>> P.S. Exceptions in constructors is a bad idea.
>>>
>>> > No, it's a very good idea. Otherwise you have to deal with half-baked
>>> > objects, which is Even Bigger Mess (tm).
>>>
>>> This is what you get when the exception is propagated out of a constructor.
>>
>> In this case I want the constructor to be rolled back.
>> Without exceptions (and rollback) the only option for handling errors
>> in initialization of (sub)components is to leave them half-baked.
>
> The point is that the constructor itself must do the roll-back, and
> leave the object in a consistent state.
>
> The rule should be:
>
>     Constructors should not propagate exceptions up; they must handle
>     all exceptions internally.

Forgive me that I contradict. The power of exceptions in a properly
designed language is, that it allows to handle problems during complex
object constructions, like

    T = new (something(new something_else ...)

and recover fully. Else we're back to testing failure after every step
again and manuall, as it was/is in C. Maybe I misunderstood the
problem altogether, though.

Regards --- Markus