220 20548 <6fb8e5c2-65a8-4a31-a8f0-7ca85b9b7247@isocpp.org> article Path: news.gmane.org!not-for-mail From: =?UTF-8?Q?Andrzej_Krzemie=C5=84ski?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Draft D0065: Movable initializer lists, rev. 2 Date: Mon, 21 Sep 2015 00:31:22 -0700 (PDT) Lines: 122 Approved: news@gmane.org Message-ID: <6fb8e5c2-65a8-4a31-a8f0-7ca85b9b7247@isocpp.org> References: <87343e65-eecd-4b96-86b7-a883aa7f9d1d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_81_1332031077.1442820683077" X-Trace: ger.gmane.org 1442820687 10826 80.91.229.3 (21 Sep 2015 07:31:27 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 21 Sep 2015 07:31:27 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDT2DGOJ34DBBTHE72XQKGQEKDXVTDA@isocpp.org Mon Sep 21 09:31:27 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f200.google.com ([209.85.213.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZdvZO-0002aM-Aw for gclcip-std-proposals@m.gmane.org; Mon, 21 Sep 2015 09:31:26 +0200 Original-Received: by igbbp9 with SMTP id bp9sf177934545igb.3 for ; Mon, 21 Sep 2015 00:31:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=gozoRsPNJrKE6o7Dm2rXvCYk8x1QUSuW2j897hf3t1w=; b=fNJPVEqBjeaxyoi0qAHNh22l3dAgwSq6n0judTNRLKINEB6sl/qJyGQown15H8+AOB ZEO+GEtzmufbmryYJObp3MjcErasjtBg+CBAbYOGR24vBrH+Vi91HkKj16ArE52IiTyG uioVfKsxozmiSBmZQtHz817FEwx2lF6uhf4NECujFZrxno34EJHzo0FWroehxa6kAZ6Z lIEGTCJUPtAlTAFF8MyvZVXvntvEi4AWJS7mMW+HVjVkXUzvmwut+EFyii+QssVAsSnM myhLMsCrrChauBXGJfmomvSC0Gve4kv4pM8cvLOzJkCh1RMVqCLa3/tkY5e05jC4yNIV QWkA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:content-type:x-original-sender:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=gozoRsPNJrKE6o7Dm2rXvCYk8x1QUSuW2j897hf3t1w=; b=hm8/cpuZPDTVibAPliqeG4vaAM9KS5TAOYY+t1JdEMlXdfwyTXqWA6Nq3864Tr6BBf la7qT1AEIYueRc627Ps1NZNB/swoli7nIPp+NT0d6aGErI5lBoSpkAwxh4VFvmsRl3wm 50IyjjFRcyGJ02L/JWhH+xjjUmR2bSZ2OSGosxe4TusQ2eGCxCFwRUbTD1rjcEM5xR9B 4KE5ZDmVfuxhHtYyifLZ2wkHzDcWTlncjLpE0sGAb4gLSPlSKRo9uHmcF6tOfPErltN9 R8axRAZX+vFsNbDnCOUrhu0gPKKHetRD9EnwAMPI8QwerUAKvOOQ1eWhFCg8IaYQjILG IFxg== X-Gm-Message-State: ALoCoQmvDI92j3xkJCq1J/Zpt7G4otmq1BeM7N52YsvGEBHrwKMgSncoJsjpK8rk97m3V2fWSOY7 X-Received: by 10.182.241.72 with SMTP id wg8mr15596444obc.2.1442820685433; Mon, 21 Sep 2015 00:31:25 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.27.4 with SMTP id p4ls760332igg.11.canary; Mon, 21 Sep 2015 00:31:24 -0700 (PDT) X-Received: by 10.50.122.103 with SMTP id lr7mr89674igb.10.1442820684247; Mon, 21 Sep 2015 00:31:24 -0700 (PDT) In-Reply-To: X-Original-Sender: akrzemi1@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:20548 Archived-At: ------=_Part_81_1332031077.1442820683077 Content-Type: multipart/alternative; boundary="----=_Part_82_1365006545.1442820683077" ------=_Part_82_1365006545.1442820683077 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable W dniu poniedzia=C5=82ek, 21 wrze=C5=9Bnia 2015 06:13:24 UTC+2 u=C5=BCytkow= nik David=20 Krauss napisa=C5=82: > > > On 2015=E2=80=9309=E2=80=9321, at 3:02 AM, Tomasz > wrote: > > I have a question regarding the rationale for keeping=20 > own_initializer_list movable. This still may lead to several dangling= =20 > reference problems, for example most common one is to treat=20 > own_initializer_list as normal container and store as class member, > > > Declaring a class member of own_initializer_list type is a diagnosable=20 > error. See the last paragraph in =C2=A72: > > This likewise requires forbidding cases where initializer_list generates= =20 > dangling pointers: when it is used as a member, a base class, the value o= f=20 > a return statement, an exception object, or the type in a *new-expression= * > . > > So, you are preventing the bug-prone constructs by a special language rule= =20 (yet another special rule to be learned by the programmers). In contrast,= =20 it appears to me that simply deleting the move constructor of=20 *own_initializer_list* would achieve the same result without adding any=20 special rule. Also, only the presence of move constructor may incorrectly= =20 suggest to the users that there is a transfer of ownership involved. So, the question is: is the move constructor necessary in your design? (BTW, Let me just mention that I really like your proposal; only with it,= =20 will initializer_list be complete.) Regards, &rzej --=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/. ------=_Part_82_1365006545.1442820683077 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

W dniu poniedzia=C5=82ek, 21 wrze=C5=9Bnia 2015 06:13:24 UTC+2 u=C5= =BCytkownik David Krauss napisa=C5=82:

On 2015=E2=80=9309=E2=80=9321, at 3:02 AM, Tomasz <toma...@gmail.com= > wrote:

I have a question regarding = the rationale for keeping own_initializer_list<T> movable. This still= may lead to several dangling reference problems, for example most common o= ne is to treat own_initializer_list<T> as normal container and store = as class member,

Declaring a cl= ass member of own_initializer_list type is a = diagnosable error. See the last paragraph in =C2=A72:

<= div>

This likewise= requires forbidding cases where initializer_list generate= s dangling pointers: when it is used as a member, a base class, the value o= f a return statement, an exception object, or the type in = a new-expression.


So, you are preventing the bug-prone constructs by a special language= rule (yet another special rule to be learned by the programmers). In contr= ast, it appears to me that simply deleting the move constructor of own_i= nitializer_list would achieve the same result without adding any specia= l rule. Also, only the presence of move constructor may incorrectly suggest= to the users that there is a transfer of ownership involved.

So, th= e question is: is the move constructor necessary in your design?

(BT= W, Let me just mention that I really like your proposal; only with it, will= initializer_list be complete.)

Regards,
&rzej

--

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