220 29884 <20161217182130.GA4347@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 19:21:30 +0100 Lines: 83 Approved: news@gmane.org Message-ID: <20161217182130.GA4347@manuel-ThinkPad-L440.localdomain> References: <20161217141109.GA22645@manuel-ThinkPad-L440.localdomain> <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> 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="82I3+IH0IqGh5yIs" X-Trace: blaine.gmane.org 1481998939 8031 195.159.176.226 (17 Dec 2016 18:22:19 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 17 Dec 2016 18:22:19 +0000 (UTC) User-Agent: Mutt/1.5.24 (2015-08-30) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDOZBAUFX4MRBWME23BAKGQEAIALA2Q@isocpp.org Sat Dec 17 19:22:14 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f69.google.com ([209.85.215.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cIJcc-0001MV-5H for gclcip-std-proposals@m.gmane.org; Sat, 17 Dec 2016 19:22:14 +0100 Original-Received: by mail-lf0-f69.google.com with SMTP id b14sf16820534lfg.6 for ; Sat, 17 Dec 2016 10:22:19 -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=1cjFBRffW1EJTP0Iy6b9VN3otzfdAoWdn79xC5AzCQo=; b=tIw6/RUIaF/NL38BZKRyThfC80vHHUvIUZzjVlk3007pKRgiCiktqY2+Z5/UHeOgYp TMUdJ4Q4Qp+mgXPeyCZIvb1v+bwM3SUtfZYCRKUK0ZZfrlejElPtrZyIHbgAgDnKYBKK SL+JNGT0tkOcVM8eU+nd9QdO2GMNR1H1m7j/q9Sg0mo/E1V8cdRqKLllAo1MnBNzre1A yCfnph5KRtigjkH0Yb6vaGjpY6UhpylOMYWTJJbGqOBLGuWHsKBuNqbQ3UYFON/kIGkr MDtdLJutmVOH+NvGVBAkk61WhPHNuvquNiO0JUENiDx6rqHlTeP6IFY4n8REK4pNEP7t gl 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=1cjFBRffW1EJTP0Iy6b9VN3otzfdAoWdn79xC5AzCQo=; b=ruxrPsFW2iymdCeqfBKnRuleyzBIbfh0bf5E87pHZIoFmiMgpE4Ku90IlZu4MbDFbx 3Dok46Evp5ELvyh2mDr4WgPk06w6l5zfK+w1cSyL/+wXJgbafl3aMW+DhjUUgMHaxdAz L2JyB/ehl6+X0DUhYUmA+D9lTYesv71melh7dHKInst3UAbLRbq/EjHK/haSActjhF6T 8N3oNgdpoGa19TFMzJ8IVE2shRVXDZxYfc5ZuwARqXAH4B2ogdOqGfqZya4ub11wk3gj uG4DRkMMRe0FFqFAy+HeaESfVKUUf4IV0TX8FXUWDL9X0vcumrMzwSzf9umOTVbcW4mr X-Gm-Message-State: AIkVDXKdIFQi3ZKmGp1rNoBa9+iihf76XfDguj+pDqwSCEt2Dosc1UsYuDhy3pfAN4wT7w== X-Received: by 10.46.71.77 with SMTP id u74mr851639lja.14.1481998938855; Sat, 17 Dec 2016 10:22:18 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.196.140 with SMTP id u134ls704812wmf.22.gmail; Sat, 17 Dec 2016 10:22:17 -0800 (PST) X-Received: by 10.194.26.170 with SMTP id m10mr7597150wjg.152.1481998937465; Sat, 17 Dec 2016 10:22:17 -0800 (PST) Original-Received: from mail-wm0-x242.google.com (mail-wm0-x242.google.com. [2a00:1450:400c:c09::242]) by mx.google.com with ESMTPS id u10si12471734wjz.151.2016.12.17.10.22.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 17 Dec 2016 10:22:17 -0800 (PST) Received-SPF: pass (google.com: domain of berglerma@gmail.com designates 2a00:1450:400c:c09::242 as permitted sender) client-ip=2a00:1450:400c:c09::242; Original-Received: by mail-wm0-x242.google.com with SMTP id u144so11238044wmu.0 for ; Sat, 17 Dec 2016 10:22:17 -0800 (PST) X-Received: by 10.28.41.5 with SMTP id p5mr8046703wmp.38.1481998936850; Sat, 17 Dec 2016 10:22:16 -0800 (PST) Original-Received: from localhost (x5d856f73.dyn.telefonica.de. [93.133.111.115]) by smtp.gmail.com with ESMTPSA id u81sm9051526wmu.10.2016.12.17.10.22.15 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 17 Dec 2016 10:22:16 -0800 (PST) Content-Disposition: inline In-Reply-To: <15884364-3238-41c7-bc5a-aa5595a64ade@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:c09::242 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:29884 Archived-At: --82I3+IH0IqGh5yIs Content-Type: text/plain; charset=UTF-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Dec 17, 2016 at 10:04:47AM -0800, Nicol Bolas wrote: > > After all, such copying behavior won't break most standard library type= s. > `vector` will work as expected, as will `any`, > `optional`, `variant`, and so forth. > It would certainly work with the STL types, but I'm fairly certain you migh= t get very different results when using these in STL algorithms. With some = implementations references to the pointees might be preserved since the alg= orithm doesn't copy the clone_ptr whereas others might perform a copy, henc= e invalidating existing references or at least having them point to a diffe= rent object than the one returned from the algorithm. > I think it's important to understand that `clone_ptr` is a solution to = a > very specific problem, one that isn't exactly common. You shouldn't see= a > huge number of these pointers lying around. > I don't think "might be harmful" is a good enough reason to not have th= e > type. Together with the fact that the problem it tries to solve isn't common it m= ost definitely is. If the type is very hard to use correctly and not really nee= ded all that often then I see no reason to have it. > I'd say the biggest problem is that there's no way to conceptualize the > special nature of `clone_ptr`'s copy constructor. You can't write a > Concepts TS `requires` clause that says, "a copy constructor/assignment > shall ensure that the copied value is =3D=3D to the original." That's a= n > axiomatic distinction, not a syntactic one. And we don't have ways to > specify axioms or require based on them. The problem really is that it tries to act both as a pointer type which wou= ld entail that after copying it the pointee is the same for both pointers a= nd at the same time it tries to be a object type where copying creates dist= inct but equivalent instances. --=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/20161217182130.GA4347%40manuel-ThinkPad-L440.loc= aldomain. --82I3+IH0IqGh5yIs Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEi3F6I6jTgMCHgGvofAJ3kFaTK3oFAlhVgigACgkQfAJ3kFaT K3o5kg//RBZW6yvORLGqaaufJRCejB6cW7TkaKIFTZqCn539EYozX8zDfRd95fLA BNrrDiavQRmEQk978bJ7fpb0ZAnrMaMZ1k7LPRd1jGw+YvnsOFzLYnhCMMqtIBhU bfSwiIJHa1w3f7/znuHje2bywVupPXY1mA/1+MhOp4yaX98O4jTWjfEbYp9KGCKz jF2vDkBl59fASGOC0TYiJ+zxjom0+5JZSvbb9Jsm0BTTRI+0x4DxHeS5F2N6S2Ix iPdnRPxroiQ9k2uQfJbeJbz+IiEgKtNKjpz5P9QmAUEK5Z93C0W/RSfR6TKYQeWu Wnne5EKOqrPTHRkib4DgZIwd2Soob3NAMKiNGTRsjPGJsIDvxJUFekhi1mnNYWA5 AknXsf4DNo2cmF0j5IW+q2NeliZYXLUdVWGePIRrsJ6C1plRDOrckOuEJSFDFuZr W13SUPFlfalXLZyz2Bqz8k00wTI77Z4I7l4PnNZKnt+Qf6JHwu35LCYqfO3K4mbu rQXJNb4QHwGkY7zXQnOmYgpOOB19hj+Z9+1kkOFTyHhpvOh0LDGkWLkONsIiKDmC 9qqFUDVqBi6WVN/Fg0UFvY0GmLmm6v8dIxwZByrCjWL7qJc/17S0xCi3Jbr0UNEI x0QIg6M7zhHbb0fiK0lST+nbLXzkqXpqZIUXcNYeaiZssdNCiMo= =KFjP -----END PGP SIGNATURE----- --82I3+IH0IqGh5yIs-- .