220 34039 <38511f1a-5d75-4c95-a240-89e19a03bbe6@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: std::vector::expand_uninitialized Date: Mon, 21 Aug 2017 18:46:26 -0700 (PDT) Lines: 101 Approved: news@gmane.org Message-ID: <38511f1a-5d75-4c95-a240-89e19a03bbe6@isocpp.org> References: <405bc3a4-4fbf-41af-b213-b24894ba2f6e@isocpp.org> <0304ee31-d873-25a5-1ff9-3364e76dff67@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_7769_1398986133.1503366386239" X-Trace: blaine.gmane.org 1503366400 29011 195.159.176.226 (22 Aug 2017 01:46:40 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 22 Aug 2017 01:46:40 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBB44Z53GAKGQEL477TJI@isocpp.org Tue Aug 22 03:46:33 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pg0-f70.google.com ([74.125.83.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1djyGs-0006T5-59 for gclcip-std-proposals@m.gmane.org; Tue, 22 Aug 2017 03:46:22 +0200 Original-Received: by mail-pg0-f70.google.com with SMTP id q3sf96471620pgr.3 for ; Mon, 21 Aug 2017 18:46:28 -0700 (PDT) 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 :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=7bnrZ21QjVJ40Uy8YU5IFHv+LRJQ8Z0BUIGW9Z/4bhw=; b=QOn4BhUR6D/07G1CbpCRuNCLUigjh/mGk8UeJJ0dY9fY+u3Ph9u8Hpk7/JSFgz1/PW HNZzK5fWGPTrOCSVawFUir2ibsrYBBJe2zDu/rYi3b4P3ZqFiP/BonpLID0mANgSjGUc x/o9nNLeo500+aCVJfLwoR0U0fv++ZCgskK9qylRCur3PMvTdpr/wJTd0G2BeBz0Hn4k u9CKocn8Y3pr9PgjwOBOLq05OMpA2e/owJZMu31fzPumfBZ1/MQtSD76pXekVjkU9L4o 1APnsKGF4BtNqWfUAq06ZomEfT5haSsjPtBbbbXCEyLLTeKIryyNd/vLBLlBbB3ew6zG T0Tw== 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 :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=7bnrZ21QjVJ40Uy8YU5IFHv+LRJQ8Z0BUIGW9Z/4bhw=; b=ozjwZpdOpuV4Y3LQtBD0LA2avK7ucPYGOPTe6DTawoHC5QpUkbmRRktc78NJ5LPPhQ 5QVRPzZcPCNOXo2q9t4krSImHU0qDBmPcPdNPLEj4/W7/OtiE1HMtnglVRn5j6e9i3mz w1BEpXrUAkMgKGSxbFa3Ve+kNI2RCbE516kXq0t1gbASdpsjIlLQ/u+0W6HjQ0YFwL7w 5phfz0NRoBAHuN0UtVqDhvQg7nNaO+vWSPi8Tvfn8mohUTkp1GYMwvBevU6h34jjsOYQ ZCJSR3UYUkDqi9KFeGsrilyqj/7D3UiRBlWUL0NQ3Rt426epskzYj5EuPVeTFWT5BDeb bd3A== 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=7bnrZ21QjVJ40Uy8YU5IFHv+LRJQ8Z0BUIGW9Z/4bhw=; b=r68o/1Zp4shtuumYVM3hNwJvlLWkn1SBPDbpifqFeO8A/NUI77UYyofVzYNyaFu7Nm s20KJx+mbvT3iqZSajMtIuLB/1CfqySSQnJ6awfLYU5sq+ATKWJgYoyFIij7tr5//80b gEUqmGiJ+uLhMXy4AWJlzZrgQEr6aGPS3lEouER16UzK6m+xF5rvj+8N2z3RXMh10+y5 dOUEj5pnSCsm9wmOE5teIkv7uvBzXiGUBKCfW+NtSEVNlpMDIFely//rvdpx6yBfJ+IJ flhStd0ZR/8uMOHqk+BhsE0fPkTIf6SJZdw4/Gfod0VFMW7SdFM6VP4/EFXW2BfcF8iv DQGw== X-Gm-Message-State: AHYfb5gJzkrZSB3PIQPNq2gs/H2+Tk7o9z9U/8O/nmQ5YY3p/EYMVZTd 9kYd0pVYA1u+Jm+L X-Received: by 10.101.69.138 with SMTP id o10mr7547991pgq.63.1503366388280; Mon, 21 Aug 2017 18:46:28 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.116.211 with SMTP id o202ls1383582itc.12.canary-gmail; Mon, 21 Aug 2017 18:46:26 -0700 (PDT) X-Received: by 10.31.160.13 with SMTP id j13mr23379vke.25.1503366386820; Mon, 21 Aug 2017 18:46:26 -0700 (PDT) In-Reply-To: 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:34039 Archived-At: ------=_Part_7769_1398986133.1503366386239 Content-Type: multipart/alternative; boundary="----=_Part_7770_1460825058.1503366386240" ------=_Part_7770_1460825058.1503366386240 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Monday, August 21, 2017 at 9:19:46 PM UTC-4, Patrice Roy wrote: > > +1. Really looks like a reserve() use-case to me. > > 2017-08-21 4:29 GMT-04:00 Jonathan M=C3=BCller >: > >> On 20.08.2017 22:22, Ryan Nicholl wrote: >> >>> My motivating example consists of a serialization routine. Ideally, the= =20 >>> serialization routine would expand the vector uninitialized and then wr= ite=20 >>> the data in. This can't be done however, because the resize function wr= ites=20 >>> 0s to the data thanks to the default allocator's construct method. >>> >> >> Could you clarify why reserve + push_back() doesn't work here? >> > 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. Again, that's a reason to allow default initialization, not to do what he= =20 suggests.=20 --=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/38511f1a-5d75-4c95-a240-89e19a03bbe6%40isocpp.or= g. ------=_Part_7770_1460825058.1503366386240 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Monday, August 21, 2017 at 9:19:46 PM UTC-4, Pa= trice Roy wrote:
+1. Really looks like a reserve() use-case to me.

2017-08-21 4:29 GMT-04:00 Jonathan M=C3=BCller <jonathanm...@gmail.com>:
On 20.08.2017 22:22, Ryan Nicholl wrote:
My motivating example consists of a serialization routine. Ideally, the ser= ialization routine would expand the vector uninitialized and then write the= data in. This can't be done however, because the resize function write= s 0s to the data thanks to the default allocator's construct method.

Could you clarify why reserve + push_back() doesn't work here?

I expect it's th= e reason he stated: he wants to prevent the value initialization of the obj= ect, since he's going to initialize it from the serialization routine. = He wants to avoid the double-initialization.

Again, that's a rea= son to allow default initialization, not to do what he suggests.
=

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