220 34041 article Path: news.gmane.org!.POSTED!not-for-mail From: Ross Smith Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: std::vector::expand_uninitialized Date: Tue, 22 Aug 2017 14:09:44 +1200 Lines: 45 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> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1503367786 20686 195.159.176.226 (22 Aug 2017 02:09:46 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 22 Aug 2017 02:09:46 +0000 (UTC) User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCQ4ZXOXM4IONJHOZQCRUBHMO4RAQ@isocpp.org Tue Aug 22 04:09:37 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f198.google.com ([209.85.220.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1djydM-0004pC-Rw for gclcip-std-proposals@m.gmane.org; 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[125.236.198.58]) by smtp.gmail.com with ESMTPSA id o18sm11512995pgd.51.2017.08.21.19.09.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 21 Aug 2017 19:09:41 -0700 (PDT) Original-Newsgroups: gmane.comp.lang.c++.isocpp.proposals In-Reply-To: <38511f1a-5d75-4c95-a240-89e19a03bbe6@isocpp.org> Content-Language: en-US X-Original-Sender: ross.smith@otoy.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@otoy-com.20150623.gappssmtp.com header.s=20150623 header.b=z9lyBedE; spf=pass (google.com: domain of ross.smith@otoy.com designates 2607:f8b0:400e:c00::233 as permitted sender) smtp.mailfrom=ross.smith@otoy.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:34041 Archived-At: On 2017-08-22 13:46, Nicol Bolas wrote: >=20 >=20 > On Monday, August 21, 2017 at 9:19:46 PM UTC-4, Patrice Roy wrote: >=20 > +1. Really looks like a reserve() use-case to me. >=20 > 2017-08-21 4:29 GMT-04:00 Jonathan M=C3=BCller >: >=20 > On 20.08.2017 22:22, Ryan Nicholl wrote: >=20 > My motivating example consists of a serialization routine. > Ideally, the serialization routine would expand the vector > uninitialized and then write the data in. This can't be done > however, because the resize function writes 0s to the data > thanks to the default allocator's construct method. >=20 >=20 > Could you clarify why reserve + push_back() doesn't work here? >=20 >=20 > I expect it's the reason he stated: he wants to prevent the value=20 > initialization of the object, since he's going to initialize it from the= =20 > serialization routine. He wants to avoid the double-initialization. >=20 > Again, that's a reason to allow default initialization, not to do what=20 > he suggests. Isn't that why we have emplace_back()? Ross Smith --=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/a3ad5bed-1f56-bdb7-d020-5361be8c186c%40otoy.com. .