220 8599 <1140684e-4619-4b14-9e0e-fdb30d830333@isocpp.org> article Path: news.gmane.org!not-for-mail From: Olaf van der Spek Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: string_view::is_null() Date: Wed, 15 Jan 2014 04:20:11 -0800 (PST) Lines: 119 Approved: news@gmane.org Message-ID: <1140684e-4619-4b14-9e0e-fdb30d830333@isocpp.org> References: <8045a4d2-721d-4725-8bb7-7a91b6f53ec8@isocpp.org> <186E0927-C962-4E34-AED0-E7509DD1F0A0@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_299_27037740.1389788411800" X-Trace: ger.gmane.org 1389788408 14833 80.91.229.3 (15 Jan 2014 12:20:08 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 15 Jan 2014 12:20:08 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC5NB45SSABBB7HZ3GLAKGQEXAQFNDI@isocpp.org Wed Jan 15 13:20:15 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ie0-f200.google.com ([209.85.223.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1W3PS9-0002rf-RR for gclcip-std-proposals@m.gmane.org; Wed, 15 Jan 2014 13:20:14 +0100 Original-Received: by mail-ie0-f200.google.com with SMTP id lx4sf5868966iec.3 for ; Wed, 15 Jan 2014 04:20:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; 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 :content-type; bh=8NR1AUktwON3tU74uZ1xkXGiyTcuyaMEQquj3zWIWKg=; b=YqeRCibt3TZfnYYPDDIOkimBTwKlavQDw0NIouVd6jr3Ic64W9OU3qmrvZ+Zrqa7mb gdq2l04gTBkaL4FqCWOsIeSYGxEAuyg+1DCYzrPulS3aLuQrrvQM/zb2nPmED2Wfu+2v Mhr26D2mQ9e933uy+ICsY5/aese89siXx6ADK7Mmi3pYGt96sQzLmniRKcBP9HYRujtt 6QyScM2DVjGlXMZl0DntKhu+R4zpRv6beDxloVO5LaI9hTcOWh+RH4d4bKH5zvKEvPzw Fvwor6EG/GBbpxmLhHN9tjZ7IzO/m1Fkno3oFWK4D6Fmkmp+6SzmE+x0Ug0COPvkraTA YAWQ== 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=8NR1AUktwON3tU74uZ1xkXGiyTcuyaMEQquj3zWIWKg=; b=OahcxTcdFd8gVUz4Z13MH9aJwzmTbYytL36K78hoJtMXVEGPc945dkymSm0yNSkzNo gQN8vxmy+87n0HgOZWnr5TqrzpfX4YNKRmpfmDqwYcUfUF+dbIWh7aA3q7AFMzo9d6lP eGaKr+ntSeF8d1Z7fjpiB5YIa7c/TerCdIFyDHZZtBIpTuMws6CdIBihxpsTmPaWfwBh FUpwj+2gbQFib2jt7MedLZfOXjzdPtJLDcPSUyjbv8cLcvXwlL3SII2RiEBOwQgph8td 8GXlyyWXgr9yFSiik41pbE+BN/PHJamEWtgoFWxFl7KXi4Brj2luIZvdswR9hiIV9znd RBgg== X-Gm-Message-State: ALoCoQnppaTaxQpBWooJ9HLB5TZ2yuP0RdckZx/G6n2eZ/XrNWXCsw4cTY0UZe/W8duvpDLMmLqG X-Received: by 10.43.161.202 with SMTP id mh10mr560890icc.23.1389788412926; Wed, 15 Jan 2014 04:20:12 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.48.105 with SMTP id k9ls532055qen.96.gmail; Wed, 15 Jan 2014 04:20:12 -0800 (PST) X-Received: by 10.49.17.98 with SMTP id n2mr35875qed.19.1389788412426; Wed, 15 Jan 2014 04:20:12 -0800 (PST) In-Reply-To: X-Original-Sender: olafvdspek@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:8599 Archived-At: ------=_Part_299_27037740.1389788411800 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Saturday, December 28, 2013 6:59:37 PM UTC+1, Jeffrey Yasskin wrote: > > i think that attempting to distinguish between an empty string_view that= =20 >> =E2=80=9Cused to point at something=E2=80=9D >> and an empty string view =E2=80=9Cthat never pointed at anything=E2=80= =9D is a use case=20 >> to be discouraged, rather than >> something that should be enshrined in the standard. >> >> This should not affect data() which returns a non-null pointer. >> >> I disagree here with the proposal as currently written. >> I believe that the requirement that data() always return a non-null=20 >> pointer is misguided.=20 >> > >> if sv.size () =3D=3D 0 or sv.empty () [same thing], there is nothing tha= t you=20 >> can do with sv.data() >> (except compare it to null, and that doesn=E2=80=99t tell you anything u= seful). >> > > The thing is, if nullptr is a possible return value for data(), people do= =20 > start using it to convey information. If they get a null out exactly when= =20 > they put a null in, it is telling them something useful. The only way to= =20 > "discourage" it is to make it never happen. If we let string_view::data()= =20 > pass through null, we're enshrining the use you don't like in the standar= d. > =20 > In some cases being able to distinguish between null and empty is required.= =20 string_view could easily support this distinction, what's the reason it=20 should be discouraged? optional is an obvious suggestion but that increases code=20 complexity at the call site when the distinction is not required. --=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. ------=_Part_299_27037740.1389788411800 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Saturday, December 28, 2013 6:59:37 PM UTC+1, Jeffrey Y= asskin wrote:
=
i think that attempting to distinguish betwe= en an empty string_view that =E2=80=9Cused to point at something=E2=80=9D
and an empty string view =E2=80=9Cthat never pointed at anything=E2=80= =9D is a use case to be discouraged, rather than
something that s= hould be enshrined in the standard.

This should not affect data() which returns a non-null = pointer.

I disagree here with the pr= oposal as currently written.
I believe that the requirement = that data() always return a non-null pointer is misguided. 

if sv.size () =3D=3D 0 or s= v.empty () [same thing], there is nothing that you can do with sv.data()
(except compare it to null, and that doesn=E2=80=99t tell you anything= useful).

The thing is, if null= ptr is a possible return value for data(), people do start using it to conv= ey information. If they get a null out exactly when they put a null in, it = is telling them something useful. The only way to "discourage" it is to mak= e it never happen. If we let string_view::data() pass through null, we're e= nshrining the use you don't like in the standard.
 
In some cases being ab= le to distinguish between null and empty is required. string_view could eas= ily support this distinction, what's the reason it should be discouraged?

optional<string_view> is an obvious suggestio= n but that increases code complexity at the call site when the distinction = is not required.

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