220 29888 <20161217192812.GA17421@manuel-ThinkPad-L440.localdomain> article Path: news.gmane.org!.POSTED!not-for-mail From: Manuel Bergler Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: New smart pointer: CopyConstructible and CopyAssignable flavor of unique_ptr Date: Sat, 17 Dec 2016 20:28:12 +0100 Lines: 103 Approved: news@gmane.org Message-ID: <20161217192812.GA17421@manuel-ThinkPad-L440.localdomain> References: <3df7e8eb-01a0-7804-f476-504b5a25a9fe@gmail.com> <20161217170428.GA10214@manuel-ThinkPad-L440.localdomain> <20161217171633.4919375.58072.21574@gmail.com> <15884364-3238-41c7-bc5a-aa5595a64ade@isocpp.org> <20161217182130.GA4347@manuel-ThinkPad-L440.localdomain> <5eae5f16-e129-4c95-8001-fc73cc4f3d03@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="UlVJffcvxoiEqYs2" X-Trace: blaine.gmane.org 1482002946 14937 195.159.176.226 (17 Dec 2016 19:29:06 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 17 Dec 2016 19:29:06 +0000 (UTC) User-Agent: Mutt/1.5.24 (2015-08-30) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDOZBAUFX4MRB7FD23BAKGQELIMDPIQ@isocpp.org Sat Dec 17 20:29:02 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f72.google.com ([209.85.215.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cIKfA-0002YN-KP for gclcip-std-proposals@m.gmane.org; Sat, 17 Dec 2016 20:28:56 +0100 Original-Received: by mail-lf0-f72.google.com with SMTP id g12sf17250569lfe.5 for ; Sat, 17 Dec 2016 11:29:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent: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=fVPvxbgE0Se3wzPbrqe4fZthoOw2nM1EIMBKWdJuApA=; b=r3cvCrGHT6ml+cR1jjHcT8C/cDWvuSA1pKlHQ+LKEYvWn20kozehW9jy3MmXavoqNs /QPPhWpW2kdZ9GAe/roFJorIJ2+9ODmSo2pQVsQNXDW8kGuGHKfaiJB5S7zuc+xP0Ey7 MAi8jC9fwpt92jGrn1WocPLyJuCRVYdW3IbAnoOY5bLzMYb2MikbCq1C9Uc2Vcy4a06J 5i4SSaZmLJnuwuuRoJPumGC4DTWJOCyj1OucmRzsW17yB9UCXgO7UNtFKtsRrkQrdTwS ckqKk3aRu8sl1sCFUDOBBtt9xph1i31OfIEVjsx+6p5oyPkQdQIpbG0B8Cqk1v+woaGH zq X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent :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=fVPvxbgE0Se3wzPbrqe4fZthoOw2nM1EIMBKWdJuApA=; b=kLw7N2/xpJRRO0bwbN2RjOpswFzqNy5x5PUlUziqYWkRseoSdwNNJyTdHTdKFBUUpq kusHhaoyZHe4rGQV4y1uDrg+pFENOEYdmBxGHo853YFct+Li5Wa3e3sfuIJhh4veEeuD bXTthjWI9W5OUUW0vo5VQUXXq4tHG1i+qFjmHluVuzJsFb/cDXA8EO1QnN8G68p86O/m bSJQUahj6c4kU65gMONoHDnwKRRjTTqSrZJfFb+qQMnOVIYix2pK2W7ru9lH4A6Qz559 KMFVy7kzY03jQ1EGBZeolzr8PFvSqzyhlZA8i/6K4xfxE12GgqqwjhyDe6+9vyCoMeSF X-Gm-Message-State: AIkVDXJ5Gde2zJMWALqf/wnVa+nD08XCs6boNqDPQzwi+ZLwx5c9ucpzKaFN0AA8fJ8Ksg== X-Received: by 10.46.78.9 with SMTP id c9mr863140ljb.27.1482002941180; Sat, 17 Dec 2016 11:29:01 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.26.13 with SMTP id a13ls698934wma.17.gmail; Sat, 17 Dec 2016 11:28:59 -0800 (PST) X-Received: by 10.28.12.80 with SMTP id 77mr8404933wmm.106.1482002939863; Sat, 17 Dec 2016 11:28:59 -0800 (PST) Original-Received: from mail-wj0-x243.google.com (mail-wj0-x243.google.com. [2a00:1450:400c:c01::243]) by mx.google.com with ESMTPS id o76si8940850wmi.60.2016.12.17.11.28.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 17 Dec 2016 11:28:59 -0800 (PST) Received-SPF: pass (google.com: domain of berglerma@gmail.com designates 2a00:1450:400c:c01::243 as permitted sender) client-ip=2a00:1450:400c:c01::243; Original-Received: by mail-wj0-x243.google.com with SMTP id kp2so18618192wjc.0 for ; Sat, 17 Dec 2016 11:28:59 -0800 (PST) X-Received: by 10.194.178.170 with SMTP id cz10mr7599143wjc.224.1482002939096; Sat, 17 Dec 2016 11:28:59 -0800 (PST) Original-Received: from localhost (x5d856f73.dyn.telefonica.de. [93.133.111.115]) by smtp.gmail.com with ESMTPSA id x188sm9249258wmx.4.2016.12.17.11.28.57 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 17 Dec 2016 11:28:58 -0800 (PST) Content-Disposition: inline In-Reply-To: <5eae5f16-e129-4c95-8001-fc73cc4f3d03@isocpp.org> X-Original-Sender: berglerma@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of berglerma@gmail.com designates 2a00:1450:400c:c01::243 as permitted sender) smtp.mailfrom=berglerma@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:29888 Archived-At: --UlVJffcvxoiEqYs2 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Dec 17, 2016 at 10:43:08AM -0800, Nicol Bolas wrote: > On Saturday, December 17, 2016 at 1:22:19 PM UTC-5, Manuel Bergler wrot= e: > > On Sat, Dec 17, 2016 at 10:04:47AM -0800, Nicol Bolas wrote: > > > > =C2=A0 After all, such copying behavior won't break most standard l= ibrary > types. > > =C2=A0 `vector` will work as expected, as will `any`, > > =C2=A0 `optional`, `variant`, and so forth. > > > > It would certainly work with the STL types, but I'm fairly certain yo= u > might get very different results when using these in STL algorithms. > With some implementations references to the pointees might be preserv= ed > since the algorithm doesn't copy the clone_ptr whereas others might > perform a copy, hence invalidating existing references or at least > having them point to a different object than the one returned from th= e > algorithm. > > Which is no different from passing a value type that gets copied, then > expecting the copies to be modifying the original value. > =C2=A0 It is different. Consider for example something like my_obj =3D std::accumulate(input.begin(), input.end(), std::move(my_obj= ), some_function); Afterwards references to my_obj will still be valid and correctly point to = the modified object. On the other hand, if you have auto f =3D [&someObj] (auto& acc, auto const& in) -> decltype(auto) { acc->doSomethingModifyingThePointeeObj(in); someObj.doSomething(acc) // note I really want the cloning here // so I need to pass in the clone_ptr // and not the pointee return std::move(acc); }; my_clone_ptr =3D std::accumulate(input.begin(), input.end(), std::move(= my_clone_ptr), f); now suddenly all references you got by calling `*my_clone_ptr` somewhen bef= ore might or might not be invalid, even though I moved the original clone_ptr i= nto the algorithm to ensure that it doesn't get copied. I'm aware that this is somewhat of a silly example because you'd probably d= o this with a handwritten for-loop, but nevertheless it shows how hard it is = to use this type correctly with STL algorithms. --=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/20161217192812.GA17421%40manuel-ThinkPad-L440.lo= caldomain. --UlVJffcvxoiEqYs2 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEi3F6I6jTgMCHgGvofAJ3kFaTK3oFAlhVkcoACgkQfAJ3kFaT K3oo+BAAoDAp81yqVbaNaoy8ySmN+V/fQix8gv8e/InMd5a/+/HEkrtKn3PqRk9I Y9PMlAJ7Eqa6JD5lk4lGaxhsH6+6/pe3REBI1xjEzEm/fjR0A4fYfGeGlPqKYwa/ nhjneYrggX2HHhaKdbPNnwrc9Q+IBiTkQBsie4r3cqzayo3Ast/TuGDEG3kB7/Sh LBiIUJv6pcpMbB/oJSwjt2MW3B8UULgvEy9p7acdhhaYotRY5qqytdsblOTYDqmS N2d9a6AOzjjI4tH5CHIMSei0j2uxvtZE86rFrhXphI5wKJvUFoPajSfgXMOjHw+7 O/rsggrHLzxaLbKoLhH+sAGun93h+MWGZCwjJlVGDOAAPNorLgjJ81nefTQtNzpk 1QOYKCN+L4SBUxGrVeLrbfOIAfmHJGmiug9+ECgisYwwH6PvDGk3D+TD6N6r2PiZ dXhO98Z/g4sbWnsNOj1X+gMr4QQ1eP6TZHGHqazZiX/TtzVGAMzAmIJBBx9I35IL 1LRHJsfMH4NXLZc/uECLkAq04NsYP7G7gMMlzpWVybbJPlLn2uU8Wwbj58GJY6gh cJtOMaJc+RJoJLDSssFAvC187bVc6ziH4a8+btPzZOgAJzGAbAAHGfYThloFG6tf ZvjeQ5f2kW6qiJOqx1FjRABYUiEnkh4Twr9mUvmEQf4yYs7GIns= =9trW -----END PGP SIGNATURE----- --UlVJffcvxoiEqYs2-- .