220 29823 article Path: news.gmane.org!.POSTED!not-for-mail From: Ville Voutilainen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: New smart pointer: CopyConstructible and CopyAssignable flavor of unique_ptr Date: Fri, 16 Dec 2016 14:11:48 +0200 Lines: 58 Approved: news@gmane.org Message-ID: References: <13702f32-32c2-447f-9996-3624fd678675@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1481890315 512 195.159.176.226 (16 Dec 2016 12:11:55 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 16 Dec 2016 12:11:55 +0000 (UTC) To: "ISO C++ Standard - Future Proposals" Original-X-From: std-proposals+bncBC5JHI7A7ALRBBNUZ7BAKGQEZFLDASQ@isocpp.org Fri Dec 16 13:11:50 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pg0-f71.google.com ([74.125.83.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cHrMY-0007Jy-FY for gclcip-std-proposals@m.gmane.org; Fri, 16 Dec 2016 13:11:46 +0100 Original-Received: by mail-pg0-f71.google.com with SMTP id q10sf179876580pgq.7 for ; Fri, 16 Dec 2016 04:11:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-transfer-encoding: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=dOtMnjR/rokyThHgYymFvUn5R02soZ7gotoQZ5al2oM=; b=F9vPu8asJnlQ4J0xTxjJpenmWFGC/1neWc2tktvfcMc3b/tc+WJTfJ7frStrkNGckJ GcO44OAkMq4i6Yn9lFKCRc4PI0+MWh810TyxFFpnwkUnnggGULYuonb/pxoorN0ZUbzS a0GX4XK3IvD0UVerVaWPZ3+mTK2cW1X4gw4VL2Qk+HDtQqDi+3zO8QaZuPL2/lB79IlA TuVAHNEA+80K8QjeI55z3St9+a6/DbhzVlS27NHXGNJoDEM53pxDvJjRpW1LMO79ZGtW fVxLrOClfRQ/x0lLr+G2Od6PyFtpOme4fswDrwIAKpBzekRMml1zFlpQ9DfbDkKMLX6l rggA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:content-transfer-encoding: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=dOtMnjR/rokyThHgYymFvUn5R02soZ7gotoQZ5al2oM=; b=o4Ais/zEILfRa/zxHeeo6iDsdErtMRjW1sspo8mBuIDmf33fUFO5x0RN8X1UllfuR3 O9MRh0DlqXv4G4jUWJd1RqXpZV2XV1BL7cRq8+G9Q1qGSsGnmANt0gbsedTwr9EW5lc/ eG5xs7maXzmhhz5J/H4rZsLHunoGGC5FEmyNLycQC983uLKtwVZxh5NJH03IMLDLdr0T k12oeOhplQ5o0sd4d0PXnZ4i277rhkac6k/zqfdpKyL+SLFTAaDIIc2CBmg0Yg1tQJgg Q9Wa+6A7AKu9ypSAJAiqMsIGmTcprbAZzhj2LLUmykwi7PTDoP7WRI2wm6mkpEmvn4YU 2qM X-Gm-Message-State: AKaTC00spy+5fH7Zof0YwU1T8Yqp1BmDmabEyeP43ruM6FkftWM4wLKx2fOf3N5nE9q14Q== X-Received: by 10.99.138.202 with SMTP id y193mr1158646pgd.121.1481890310558; Fri, 16 Dec 2016 04:11:50 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.1.164 with SMTP id e33ls8164261ote.43.gmail; Fri, 16 Dec 2016 04:11:49 -0800 (PST) X-Received: by 10.176.1.112 with SMTP id 103mr1789278uak.154.1481890309154; Fri, 16 Dec 2016 04:11:49 -0800 (PST) Original-Received: from mail-ua0-x234.google.com (mail-ua0-x234.google.com. [2607:f8b0:400c:c08::234]) by mx.google.com with ESMTPS id j2si2137663uad.92.2016.12.16.04.11.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Dec 2016 04:11:49 -0800 (PST) Received-SPF: pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:400c:c08::234 as permitted sender) client-ip=2607:f8b0:400c:c08::234; Original-Received: by mail-ua0-x234.google.com with SMTP id b35so8438799uaa.0 for ; Fri, 16 Dec 2016 04:11:49 -0800 (PST) X-Received: by 10.176.65.33 with SMTP id j30mr2260123uad.94.1481890308777; Fri, 16 Dec 2016 04:11:48 -0800 (PST) Original-Received: by 10.103.50.74 with HTTP; Fri, 16 Dec 2016 04:11:48 -0800 (PST) In-Reply-To: X-Original-Sender: ville.voutilainen@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:400c:c08::234 as permitted sender) smtp.mailfrom=ville.voutilainen@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:29823 Archived-At: On 16 December 2016 at 14:05, Jonathan M=C3=BCller wrote: > On Dec 16, 2016 12:48, "Ville Voutilainen" > wrote: >> >> Right, and I think My Little Pony is under-appreciated, but if I >> really want to convey useful information to anyone, >> I explain why. Those semantics happen to be superior to the alternatives= .. > > Take std::optional, when you move it the old optional will not become emp= ty: > move does basically the same as copy, just uses T's copy instead of move > constructor. > And this behavior makes sense: optional is supposed to behave like a T= .. > > std::unique_ptr on the other hand is only moveable and transfers ownershi= p. > This also makes sense. > > Now, std::optional does not work with polymorphic objects. So I see a poi= nt > for a smart pointer with deep copying semantics. But then it should behav= e > like the type so moving should also da a "move clone". > > Now consider a smart pointer with deep copying semantics but ownership > transfer on move: What is it supposed to model? It does not behave like t= he > type T as moving does something different. > > Consider using the pointer with a type that is only copyable. If you have > code that takes a reference directly and (somehow) invokes a move operati= on, > the move will copy, so it is safe to use moved-from object there. But if = you > use that with this smart pointer, it is not safe anymore, as the pointer > will become null. > > I personally think that this kind of semantic difference is not a good id= ea. That semantic difference allows doing noexcept moves, which ends up being such a major win that quite many people are able to tolerate this trade-off. --=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/CAFk2RUb4-hGZq8ZDNR%3DeMv2erJK%2B8UH8Qj%3DSNeG%2= B9DBW678Wkw%40mail.gmail.com. .