220 16116 <56A0729B-434D-4300-B4FF-5D744D81506C@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: deprecate catch exception by value, at least in some instances? Date: Mon, 9 Feb 2015 06:55:38 +0800 Lines: 89 Approved: news@gmane.org Message-ID: <56A0729B-434D-4300-B4FF-5D744D81506C@gmail.com> References: <8be36e16-97f4-4d8a-8500-c045195b2f6b@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2070.6\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_0F59AFC3-D707-4A25-9BCD-0A3A41FB36B0" X-Trace: ger.gmane.org 1423436157 27980 80.91.229.3 (8 Feb 2015 22:55:57 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 8 Feb 2015 22:55:57 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRB5WS36TAKGQEFWKC53Q@isocpp.org Sun Feb 08 23:55:53 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qa0-f70.google.com ([209.85.216.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YKalc-0000iL-Ab for gclcip-std-proposals@m.gmane.org; Sun, 08 Feb 2015 23:55:52 +0100 Original-Received: by mail-qa0-f70.google.com with SMTP id v8sf67955641qal.1 for ; Sun, 08 Feb 2015 14:55:51 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:content-type:message-id:mime-version :subject:date:references:to:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=F+23sryJ0Lxo/0B/dQSGPDE4T7MdqcI3DmqcEGSTK28=; b=mjaFBK9gZFBOD9vph6pFJoxQWOt5AkAxBSO+GKJ235fx3df2JqOuNWDP0zWHRzHDNm hNlCQZEHZ0kqg8q4hbvsuSqrAH3dM/gil94EUEbK5S2XtTUM6M6tPVLWiTj+oCg80foz ixjgAjeA2iSHmSJlM7sM0aBdV0/XV2/Sq3SZ4Y0FuyTr1RJIWaMnxKfppuNENe8wvvRs GCUFLzYbq4rNSCW2COpINCKIGtTL6E4SxuUUZNf3d5Q+t76mAdhxVZ28aJIiIcdg02d7 GwVUbTkGT/2hMCCgh8LDm3zNzS+aAdveo9QPQheKg4BLc8AGC0ZPL47/sT/yBItpu3xY 9Exw== X-Gm-Message-State: ALoCoQnuqGGyw8wtoP8PsNTBEN2hljcl327My3651j8byVD1qamtu/KOkdp429x08j0YQmuUoSeI X-Received: by 10.236.24.228 with SMTP id x64mr13284546yhx.26.1423436151451; Sun, 08 Feb 2015 14:55:51 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.6.25 with SMTP id 25ls1442178iog.79.gmail; Sun, 08 Feb 2015 14:55:50 -0800 (PST) X-Received: by 10.66.55.104 with SMTP id r8mr23151804pap.75.1423436150810; Sun, 08 Feb 2015 14:55:50 -0800 (PST) Original-Received: from mail-pd0-f172.google.com (mail-pd0-f172.google.com. [209.85.192.172]) by mx.google.com with ESMTPS id oz9si19711195pdb.15.2015.02.08.14.55.50 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 08 Feb 2015 14:55:50 -0800 (PST) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 209.85.192.172 as permitted sender) client-ip=209.85.192.172; Original-Received: by pdjz10 with SMTP id z10so26882982pdj.13 for ; Sun, 08 Feb 2015 14:55:50 -0800 (PST) X-Received: by 10.70.56.6 with SMTP id w6mr23832298pdp.69.1423436150675; Sun, 08 Feb 2015 14:55:50 -0800 (PST) Original-Received: from [172.20.10.2] ([121.54.44.93]) by mx.google.com with ESMTPSA id ew7sm14332161pdb.65.2015.02.08.14.55.48 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 08 Feb 2015 14:55:50 -0800 (PST) In-Reply-To: <8be36e16-97f4-4d8a-8500-c045195b2f6b@isocpp.org> X-Mailer: Apple Mail (2.2070.6) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 209.85.192.172 as permitted sender) smtp.mail=potswa@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:16116 Archived-At: --Apple-Mail=_0F59AFC3-D707-4A25-9BCD-0A3A41FB36B0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 > On 2015=E2=80=9302=E2=80=9309, at 6:42 AM, gmisocpp@gmail.com wrote: >=20 > A more graphic example note my_base destructs twice but constructs once: You=E2=80=99re not seeing the copy (by slice) constructor. If you don=E2=80=99t want a base exception class to be sliced, you can cons= ider making it abstract. I don=E2=80=99t really see any problem in getting = a std::exception value, though. On the other hand, catching a base class by value gives the catch block its= own modifiable copy. This might not be very useful, and might seldom refle= ct a strong intent of the programmer, but there=E2=80=99s no other way to a= chieve it than to initialize the parameter by value. Deprecation would seem= gratuitous. > Again no warning. Would anyone ever want this in this circumstance? I=E2=80=99ve never really wanted a catch by value, but it does give the blo= ck the opportunity to choose between throwing a modified copy, and re-throw= ing to resume unwinding without any change. --=20 ---=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. --Apple-Mail=_0F59AFC3-D707-4A25-9BCD-0A3A41FB36B0 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=UTF-8
On 2015=E2=80=9302= =E2=80=9309, at 6:42 AM, g= misocpp@gmail.com wrote:

<= div class=3D"">
A more graphic example&nb= sp; note my_base destructs twice but constructs once:

You=E2=80=99re not seeing the copy = (by slice) constructor.

If you don=E2=80=99t want a base exception class to be sliced, you c= an consider making it abstract. I don=E2=80=99t really see any problem in g= etting a std::exception value, tho= ugh.

On the other= hand, catching a base class by value gives the catch block its own modifia= ble copy. This might not be very useful, and might seldom reflect a strong = intent of the programmer, but there=E2=80=99s no other way to achieve it th= an to initialize the parameter by value. Deprecation would seem gratuitous.=

Again no warning. Would anyone ever wa= nt this in this circumstance?

I=E2=80=99ve never really wanted a catch by value, but it does gi= ve the block the opportunity to choose between throwing a modified copy, an= d re-throwing to resume unwinding without any change.

--

---
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/<= /a>.
--Apple-Mail=_0F59AFC3-D707-4A25-9BCD-0A3A41FB36B0-- .