220 29842 article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: New smart pointer: CopyConstructible and CopyAssignable flavor of unique_ptr Date: Fri, 16 Dec 2016 08:06:14 -0800 (PST) Lines: 102 Approved: news@gmane.org Message-ID: References: <13702f32-32c2-447f-9996-3624fd678675@isocpp.org> <67a9e9ed-8748-4098-a43b-33598b516464@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_735_616581044.1481904374400" X-Trace: blaine.gmane.org 1481904387 9069 195.159.176.226 (16 Dec 2016 16:06:27 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 16 Dec 2016 16:06:27 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBB55B2DBAKGQEZWE27HY@isocpp.org Fri Dec 16 17:06:14 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f200.google.com ([209.85.192.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cHv1P-0000PA-Gf for gclcip-std-proposals@m.gmane.org; Fri, 16 Dec 2016 17:06:11 +0100 Original-Received: by mail-pf0-f200.google.com with SMTP id i88sf123563896pfk.3 for ; Fri, 16 Dec 2016 08:06:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :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=wDlurT28YfkluXtM4vkWyPhtEPXXoQD62yO4D2ll/Gw=; b=OAX+PVxkgGW08SIKca+0SYd62sgMyfmrZk02NYkxZ1AzZcL2fGh4CsQ6TWlxj9rmY3 I1m/x5LBuMzroAxmTDaSefGS8BPDzP6NOVIKPHtJtr5nYXvuxF+jJme43T0GcxN2DPmi HiDQQAORoSuF++MQY9But0WJDxJkOTj27gQDS3iow9nBk+gDPYR+lOme7bkDPQ2pox5l xJlXKovRCXnqswCkSioUBmEk4/CL9pgX1Fqr0BDnjOkoGPFV12QtalnC/A9A801ZMU6N EENU69Vl2oemwtatTG5i5TbdN1IvRGRjvyCAobKUQIBFE0XBxXI2/5yKPQbXAKTi6bDe yadg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :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=wDlurT28YfkluXtM4vkWyPhtEPXXoQD62yO4D2ll/Gw=; b=PRCQUuqezOP8HeG5rWRX12O687jICdbYvlDHbmIHt2iH6gIba33opxPcZ/TJWzACgJ HM2IPpf79BL1AQepfX6/aoBTFlN7YKVki9/VLuMsTZnWnu39TYtji9CnjMzp9H13R5ca ySFWewNHfyB3RDDZPCPW2G5srFsQKaG6PmcIr6lSIR6pjRMlc0jY2WftYo+47KanVSkz pjMetBTHGvDXt28CYypTSc1ha+RP5oN1RvRMlsk1FCB7dnSQeT3eGmvGzhzGcUkG22cK l84Q8wuvbAV0GTHrYOLI4qLojFVtHa3U/f+XVtZXoe7k5d4yTtbWQiLVebS1AI9eY60Z +drA== 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:message-id:in-reply-to:references :subject:mime-version: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=wDlurT28YfkluXtM4vkWyPhtEPXXoQD62yO4D2ll/Gw=; b=aBTzQSESN5HcgAKZtsEJRmv3rnL9MNoNQyIwje4+U/ya7oPbE6PZsLhX6fU8p/WX4N EnP0rMIQdAmaffCwrqBbHgMiuWA8iLF1sZOL1dFgXQZDkKcWKhtIs7oE54nQFdSXVPip eNSBSdKkdpvoERoshc2zMGV39XK1eCEfu69CI/bE8fyUN9rhCp8dU2ZbYvIoi191c2+X h+SPy2IgdEM1TvUV2wH64T6WX4LCo/DkgJrQA6neshD7Zhw5c5FeYG133zD3ZPdBiAQ8 vX92JkAxpD0ePbawC+mRq9gz1gktoDz/mChN7tSGW/MfUioyZKyNXdbNcV2DmQyMHs09 Qeqg== X-Gm-Message-State: AKaTC016l7E74p+O4qlidBYbyOcnP4K3TayCVyyMfjS1cbroouVNWO3SwNDh63vQBZ0pKQ== X-Received: by 10.99.36.1 with SMTP id k1mr1727405pgk.25.1481904375671; Fri, 16 Dec 2016 08:06:15 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.11.2 with SMTP id a2ls8481300ota.16.gmail; Fri, 16 Dec 2016 08:06:14 -0800 (PST) X-Received: by 10.157.37.125 with SMTP id j58mr195218otd.18.1481904374798; Fri, 16 Dec 2016 08:06:14 -0800 (PST) In-Reply-To: <67a9e9ed-8748-4098-a43b-33598b516464@isocpp.org> X-Original-Sender: jmckesson@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:29842 Archived-At: ------=_Part_735_616581044.1481904374400 Content-Type: multipart/alternative; boundary="----=_Part_736_1931310412.1481904374400" ------=_Part_736_1931310412.1481904374400 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Friday, December 16, 2016 at 10:46:28 AM UTC-5, Nicol Bolas wrote: > > On Friday, December 16, 2016 at 6:58:40 AM UTC-5, Jonathan Wakely wrote: >> >> On Friday, 16 December 2016 11:44:40 UTC, Jonathan M=C3=BCller wrote: >>> >>> So it transfers ownership when moving and does a deep copy when copying= ? >>> >>> I don't think two so different semantics are a great idea. >>> >>> >>> >> That seems to work for std::vector, and many other types. >> > > I really think this needs to be emphasized. Cheap-move+deep-copy are=20 > hardly an uncommon set of semantics in C++. Every standard library=20 > container uses these semantics. > > The only question is how deep the copy goes: whether you're creating a `T= `=20 > itself or some class derived from `T`. > Oh, and one more C++ standard library type that has these semantics: `any`.= =20 It requires that the types provided are copyable, and on copying an `any`,= =20 it will perform a copy (of the exact type provided, of course). However,=20 the move may be merely a pointer-shift (to support small object=20 optimization, `any`s that store objects with noexcept moves may use the=20 object's move constructor instead of the `any` pointer-shift). --=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/ad1bfe2f-c769-4938-9f92-8f6b396f03e6%40isocpp.or= g. ------=_Part_736_1931310412.1481904374400 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Friday, December 16, 2016 at 10:46:28 AM UTC-5, Nicol B= olas wrote:
On= Friday, December 16, 2016 at 6:58:40 AM UTC-5, Jonathan Wakely wrote:
On Friday, 16 December = 2016 11:44:40 UTC, Jonathan M=C3=BCller wrote:

So it transfers ownership when moving and does a= deep copy when copying?

I don't think two so different semantics are a great ide= a.



That seems to work = for std::vector, and many other types.

I r= eally think this needs to be emphasized. Cheap-move+deep-copy are hardly an= uncommon set of semantics in C++. Every standard library container uses th= ese semantics.

The only question is how deep the copy goes: whether = you're creating a `T` itself or some class derived from `T`.
<= /div>

Oh, and one more C++ standard library type that = has these semantics: `any`. It requires that the types provided are copyabl= e, and on copying an `any`, it will perform a copy (of the exact type provi= ded, of course). However, the move may be merely a pointer-shift (to suppor= t small object optimization, `any`s that store objects with noexcept moves = may use the object's move constructor instead of the `any` pointer-shif= t).

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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/ad1bfe2f-c769-4938-9f92-8f6b396f03e6= %40isocpp.org.
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