220 34056 article Path: news.gmane.org!.POSTED!not-for-mail From: Nevin Liber Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: std::vector::expand_uninitialized Date: Tue, 22 Aug 2017 09:52:51 -0500 Lines: 82 Approved: news@gmane.org Message-ID: References: <405bc3a4-4fbf-41af-b213-b24894ba2f6e@isocpp.org> <0304ee31-d873-25a5-1ff9-3364e76dff67@gmail.com> <38511f1a-5d75-4c95-a240-89e19a03bbe6@isocpp.org> <2e2acdaf-58ae-4be9-a541-28d0291a09d4@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="94eb2c1197ba528341055758c2d0" X-Trace: blaine.gmane.org 1503413614 20873 195.159.176.226 (22 Aug 2017 14:53:34 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 22 Aug 2017 14:53:34 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBCE35H5S6IDBB3MK6HGAKGQEGSIUZVY@isocpp.org Tue Aug 22 16:53:30 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qt0-f200.google.com ([209.85.216.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dkAYa-00054g-5t for gclcip-std-proposals@m.gmane.org; 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[2607:f8b0:400e:c05::233]) by mx.google.com with ESMTPS id u16si9805657plk.164.2017.08.22.07.53.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 22 Aug 2017 07:53:33 -0700 (PDT) Received-SPF: pass (google.com: domain of nliber@gmail.com designates 2607:f8b0:400e:c05::233 as permitted sender) client-ip=2607:f8b0:400e:c05::233; Original-Received: by mail-pg0-x233.google.com with SMTP id s14so11757328pgs.1 for ; Tue, 22 Aug 2017 07:53:33 -0700 (PDT) X-Received: by 10.84.175.132 with SMTP id t4mr1085887plb.195.1503413612477; Tue, 22 Aug 2017 07:53:32 -0700 (PDT) Original-Sender: nliber@gmail.com Original-Received: by 10.100.133.80 with HTTP; Tue, 22 Aug 2017 07:52:51 -0700 (PDT) In-Reply-To: X-Original-Sender: nevin@eviloverlord.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=ox2yF5Kt; spf=pass (google.com: domain of nliber@gmail.com designates 2607:f8b0:400e:c05::233 as permitted sender) smtp.mailfrom=nliber@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:34056 Archived-At: --94eb2c1197ba528341055758c2d0 Content-Type: text/plain; charset="UTF-8" On Tue, Aug 22, 2017 at 9:34 AM, Ville Voutilainen < ville.voutilainen@gmail.com> wrote: > Trying to fix vector's performance > problems one by one runs the risk of breaking vector's class > invariants, which (all of them) somebody > somewhere is bound to rely on, so I'd expect fair amounts of > resistance to such an approach. Nicol isn't breaking vector's invariants with his proposal. He is looking to add default-initialization in addition to the normal zero-initialization usually performed with allocators; for classes with default constructors, there is no difference. One thing that bugs me about his proposal is that he is changing allocator_traits from a class which always forwards to the allocator if it can into a class which will always perform default-initialization in this one case. This isn't to say that there shouldn't be a low-level utility, but I'd still like to have this functionality as well, without having to resort to a custom allocator, and definitely without breaking vector's invariants. -- Nevin ":-)" Liber +1-847-691-1404 -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAGg_6%2BM%2BfCjSm5RQGStWXaAegpx0kZsnNw%3Deojvoqnw6SCh-tQ%40mail.gmail.com. --94eb2c1197ba528341055758c2d0 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Tue, Aug 22, 2017 at 9:34 AM, Ville Voutilainen <ville.voutilainen@gmail.com> wrote:
Trying = to fix vector's performance
problems one by one runs the risk of breaking vector's class
invariants, which (all of them) somebody
somewhere is bound to rely on, so I'd expect fair amounts of
resistance to such an approach.

Nicol isn&#= 39;t breaking vector's invariants with his proposal.=C2=A0 He is lookin= g to add default-initialization in addition to the normal zero-initializati= on usually performed with allocators; for classes with default constructors= , there is no difference.=C2=A0 One thing that bugs me about his proposal i= s that he is changing allocator_traits from a class which always forwards t= o the allocator if it can into a class which will always perform default-in= itialization in this one case.

This isn't to s= ay that there shouldn't be a low-level utility, but I'd still like = to have this functionality as well, without having to resort to a custom al= locator, and definitely without breaking vector's invariants.
--
=
=C2=A0Nevin ":-)" Lib= er=C2=A0 <mailto:nevin@eviloverlord.com> =C2=A0+1-847-691-1404
=

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