220 8739 <0a730641-1b13-4290-8c01-5420515a1482@isocpp.org> article Path: news.gmane.org!not-for-mail From: Peter Bigot Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: string_view::is_null() Date: Mon, 20 Jan 2014 05:13:11 -0800 (PST) Lines: 122 Approved: news@gmane.org Message-ID: <0a730641-1b13-4290-8c01-5420515a1482@isocpp.org> References: <104254A6-C69A-4571-8455-89D7E466D493@gmail.com> <6a95bf9c-55c9-4ae2-966f-d1b1f4df6a37@isocpp.org> <52D9E336.1060801@knejp.de> <1B534FD7-B385-4A7E-A718-3C73F0AB61DC@gmail.com> <11f13f8f-1270-427c-8942-94027a181ff4@isocpp.org> <20140119174431.GA16875@faust.lysator.liu.se> <20140119192238.GA19497@faust.lysator.liu.se> <60842af6-5ec4-4364-b2d5-a0be9d578bd6@isocpp.org> <6c82c4ae-c144-443a-81b2-ea1a6b645601@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_699_2367907.1390223591514" X-Trace: ger.gmane.org 1390223586 9639 80.91.229.3 (20 Jan 2014 13:13:06 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 20 Jan 2014 13:13:06 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDA3LUEAQACBB2GB6SLAKGQEHGHETKY@isocpp.org Mon Jan 20 14:13:14 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vc0-f197.google.com ([209.85.220.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1W5EfC-0008Av-1g for gclcip-std-proposals@m.gmane.org; Mon, 20 Jan 2014 14:13:14 +0100 Original-Received: by mail-vc0-f197.google.com with SMTP id hq11sf11669966vcb.4 for ; Mon, 20 Jan 2014 05:13:13 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; 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:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=N5foJTk/BKp6SjotVTWjkYYdkgWYHeUItoVOnVG4l18=; b=hyvYeFdTbCSqdBMdiYGzXMVg96cva/t4pc6m0owMv1bPMEPm/eqPVtdIFd0abGvaj7 JbwMRkQdfwl/Rx4HcLKI0dchnEMbAyrO23hrWnx8OFQOgabAm3vwPHU86rbol5udIxlw OUNWLFnX1aFn7iiyJmohk0rLAgDKREuFQsgMmwMBXgyNRG+89qcbdotkfe86ayjbDI3A ZKxioig0kbPwN8k4SblcUdLP35snOLcgnwwskEDhYgmYF3T/c99/kiGGTU3BU48NhOck cvVibk6ySiUH3DqO+w3eaejvlPWumARnOUuiuSwDO1WFTAydZQDjHkaE1VK278ZK88kN cDmA== X-Gm-Message-State: ALoCoQms0y58eTV9dlOS69PwmuKJHCtqB8USE22N7euVbiXwE52lyt9lw5cOH7LPrO6JgWNvagtP X-Received: by 10.236.180.2 with SMTP id i2mr5342005yhm.4.1390223593043; Mon, 20 Jan 2014 05:13:13 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.182.19.165 with SMTP id g5ls919832obe.59.gmail; Mon, 20 Jan 2014 05:13:12 -0800 (PST) X-Received: by 10.182.73.228 with SMTP id o4mr5484obv.34.1390223592139; Mon, 20 Jan 2014 05:13:12 -0800 (PST) In-Reply-To: X-Original-Sender: bigotp@acm.org 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:8739 Archived-At: ------=_Part_699_2367907.1390223591514 Content-Type: text/plain; charset=UTF-8 On Monday, January 20, 2014 1:36:00 AM UTC-6, Jeffrey Yasskin wrote: > > On Sun, Jan 19, 2014 at 10:25 PM, Nevin Liber > > wrote: > > On 20 January 2014 00:12, Jeffrey Yasskin > > wrote: > >> > >> > My personal preference for all this is that string_view(nullptr, 0) > be > >> > allowed, and it is a Quality of Implementation issue whether or not > >> > sv.data() can ever return a nullptr; i.e., it would be allowed to > return > >> > any > >> > legal pointer it wants for an empty string_view. > >> > >> That's interesting. It's easier to both specify and implement to just > >> say that string_view(x, y).data()==x and string_view(x, y).size()==y, > >> assuming [x, x+y) is a valid range. Why would you special-case data() > >> to return arbitrary things when y==0? > > > > > > A debugging implementation may want to ensure that developers aren't > > dependent on "knowing" that a nullptr was passed in. > > Thanks. I think I don't personally want that, but I've added your > reason to the "if we want data()==nullptr" section in the attached > draft. I plan to send this to Clark tomorrow (Monday) morning. > I believe your alternative section also needs something like: In subclause "x.1 basic_string_view constructors and assignment operators [string.view.cons]" basic_string_view(const charT* str); Requires: [str,str + traits::length(str)) is a valid range, or that str is a null pointer value along with setting the size() to zero in the added case, if I'm correct in my understanding that traits::length(str) is undefined when str is null. Peter -- --- 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. 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On Monday, January 20, 2014 1:36:00 AM UTC-6, Jeff= rey Yasskin wrote:
On Sun, Jan = 19, 2014 at 10:25 PM, Nevin Liber <= ne...@eviloverlord.com> wrote:
> On 20 January 2014 00:12, Jeffrey Yasskin <jyas...@google.com> wrote:
>>
>> > My personal preference for all this is that string_view(n= ullptr, 0) be
>> > allowed, and it is a Quality of Implementation issue whet= her or not
>> > sv.data() can ever return a nullptr; i.e., it would be al= lowed to return
>> > any
>> > legal pointer it wants for an empty string_view.
>>
>> That's interesting. It's easier to both specify and implement = to just
>> say that string_view(x, y).data()=3D=3Dx and string_view(x, y)= ..size()=3D=3Dy,
>> assuming [x, x+y) is a valid range. Why would you special-case= data()
>> to return arbitrary things when y=3D=3D0?
>
>
> A debugging implementation may want to ensure that developers aren= 't
> dependent on "knowing" that a nullptr was passed in.

Thanks. I think I don't personally want that, but I've added your
reason to the "if we want data()=3D=3Dnullptr" section in the attached
draft. I plan to send this to Clark tomorrow (Monday) morning.
 
I believe your alternative section also nee= ds something like:

In subclause "x.1 basic_string_view constructors = and assignment operators [string.view.cons]"

    bas= ic_string_view(const charT* str);
    Requires: [str,str = + traits::length(str)) is a valid range, or that str is a null pointer valu= e

along with setting the size() to zero in the added case, if I'm co= rrect in my understanding that traits::length(str) is undefined when str is= null.

Peter

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