220 20545 article Path: news.gmane.org!not-for-mail From: =?UTF-8?Q?Tomasz_Kami=C5=84ski?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Draft D0065: Movable initializer lists, rev. 2 Date: Mon, 21 Sep 2015 07:41:13 +0200 Lines: 101 Approved: news@gmane.org Message-ID: 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/alternative; boundary=001a11c1a0e65bd65805203b5442 X-Trace: ger.gmane.org 1442814079 5059 80.91.229.3 (21 Sep 2015 05:41:19 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 21 Sep 2015 05:41:19 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDNPVXXG6IGBB6VQ72XQKGQEYDTHS7I@isocpp.org Mon Sep 21 07:41:17 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yk0-f197.google.com ([209.85.160.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Zdtqn-0002ee-8M for gclcip-std-proposals@m.gmane.org; Mon, 21 Sep 2015 07:41:17 +0200 Original-Received: by ykdg206 with SMTP id g206sf159615199ykd.1 for ; Sun, 20 Sep 2015 22:41:16 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=670+zmdT/wAYdV8qtFXyLL3Ix2ZvvLCv7phNuGTMNfk=; b=WUgDTusIUCxsM5/TdjaIXW0mIeHxgPGrWoPWFUVZy5sdjdnQdTOkDONdxxSh31wDpn gbwnRHVN5ww5hJSKyTo3WRom2kx25lUeZS+fgJuOFVc2FG5dwp0XXKLvK2cdnPeVaBb0 /FNZ8f+vevNRhpxJYU9JSCWkwMHdWIus3vyVqSsVuSd5CMfg/oFFibYYFdQMSM248Bqu e9LLu7cAd7zWQKiNSFd5KSMPXxSTQ49+9hjmyo6zLyQcYqLjxE7ev983OPuZ+Ywmqrae K8WcqMORqm5m2N61ctQFpusIkpPnwDLIINw+lBVu0fbI79g3LTDyNkysoVD5Ed0GAy/v 3IrQ== X-Gm-Message-State: ALoCoQmimrzmM7mijdIbUzWcwp/X0rIu9UPi1gBezyNsLIprGeY8g+5wg3jiSdvjr/8jq4uh03Vz X-Received: by 10.13.204.130 with SMTP id o124mr15534412ywd.36.1442814076499; Sun, 20 Sep 2015 22:41:16 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.182.65.163 with SMTP id y3ls675583obs.66.gmail; Sun, 20 Sep 2015 22:41:14 -0700 (PDT) X-Received: by 10.60.117.197 with SMTP id kg5mr10878803oeb.36.1442814074278; Sun, 20 Sep 2015 22:41:14 -0700 (PDT) Original-Received: from mail-ob0-x22f.google.com (mail-ob0-x22f.google.com. [2607:f8b0:4003:c01::22f]) by mx.google.com with ESMTPS id xj4si11131099oeb.73.2015.09.20.22.41.14 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 20 Sep 2015 22:41:14 -0700 (PDT) Received-SPF: pass (google.com: domain of tomaszkam@gmail.com designates 2607:f8b0:4003:c01::22f as permitted sender) client-ip=2607:f8b0:4003:c01::22f; Original-Received: by obbmp4 with SMTP id mp4so40275611obb.3 for ; Sun, 20 Sep 2015 22:41:14 -0700 (PDT) X-Received: by 10.60.69.2 with SMTP id a2mr10228594oeu.3.1442814074015; Sun, 20 Sep 2015 22:41:14 -0700 (PDT) Original-Received: by 10.202.87.82 with HTTP; Sun, 20 Sep 2015 22:41:13 -0700 (PDT) In-Reply-To: X-Original-Sender: tomaszkam@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of tomaszkam@gmail.com designates 2607:f8b0:4003:c01::22f as permitted sender) smtp.mailfrom=tomaszkam@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-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:20545 Archived-At: --001a11c1a0e65bd65805203b5442 Content-Type: text/plain; charset=UTF-8 2015-09-21 6:11 GMT+02:00 David Krauss : > > Both situations are non-trivial to understand and requires knowledge about > internal implementation (stack array) and are source of errors in the > program. Both of them would be fixed by making the own_initializer_list > non-copyable and non-moveable. > > > That would not be sufficient as a fix, because constructing an initializer > list object from a braced-init-list does not always involve an intermediate > temporary that needs to be moved. > Ok, I agree. Your are pointing that in my example I could use construct as follows: struct Composite { Composite(own_initializer_list&& a_list) : a_list(m_list) {} Composite() : a_list{std::make_unique(), std::make_unique()} private: own_initializer_list m_list; }; Then Composite c; will lead to dangling reference. However, I still think that removing the move-constructor would be beneficial. The existence of the move-constructor and the name (own_initializer_list) suggest that the list object actually manages storage and moves it from one object to another. As the own_initializer_list is effectively wrapped reference to stack allocated array, it cannot do that, so the current design is misleading. What is motivation for own_initializer_list being move-able? It's existence suggest user that the class behaves more like unique_ptr than reference to stack array. -- --- 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 email 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-proposals/. --001a11c1a0e65bd65805203b5442 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

= 2015-09-21 6:11 GMT+02:00 David Krauss <potswa@gmail.com>:

Both situations are non-trivial to understand and requires knowl= edge about internal implementation (stack array) and are source of errors i= n the program. Both of them would be fixed by making the own_initializer_li= st non-copyable and non-moveable.

<= /span>
That would not be sufficient as a fix, because constructing an i= nitializer list object from a braced-init-list does not always involve an i= ntermediate temporary that needs to be moved.


Ok, I agree. Your are pointing that in my example I could use= construct as follows:
struct Composite
{
=C2=A0 Composite(own_ini= tializer_list<ComponentPtr>&& a_list) : a_list(m_list) {}
= =C2=A0 Composite() : a_list{std::make_unique<ConcreteComposite1>(), s= td::make_unique<ConcreteComposite2>()}=C2=A0

private:
=C2= =A0 own_initializer_list<ComponentPtr> m_list;
};
Then Composit= e c; will lead to dangling reference.

However, I still think that re= moving the move-constructor would be beneficial. The existence of the move-= constructor and the name (own_initializer_list) suggest that the list objec= t actually manages storage and moves it from one object to another. As the = own_initializer_list is effectively wrapped reference to stack allocated ar= ray, it cannot do that, so the current design is misleading.

<= div>What is motivation for own_initializer_list being move-able? It's e= xistence suggest user that the class behaves more like unique_ptr<T[]>= ; than reference to stack array.

--

---
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>.
--001a11c1a0e65bd65805203b5442-- .