220 35106 <5005582.pCRZNEiGFO@tjmaciei-mobl1> article Path: news.gmane.org!.POSTED!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Marking more std::string_view members noexcept Date: Wed, 25 Oct 2017 19:16:55 -0700 Lines: 50 Approved: news@gmane.org Message-ID: <5005582.pCRZNEiGFO@tjmaciei-mobl1> References: <3d03cd7d-2177-98fd-408d-f74b1f6a8552@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" X-Trace: blaine.gmane.org 1508984218 486 195.159.176.226 (26 Oct 2017 02:16:58 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 26 Oct 2017 02:16:58 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBGULYXHQKGQE7KRRRZY@isocpp.org Thu Oct 26 04:16:54 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f69.google.com ([74.125.82.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1e7Xj2-0007rP-7X for gclcip-std-proposals@m.gmane.org; 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[78.47.120.188]) by mx.google.com with ESMTP id t9si173237wmt.36.2017.10.25.19.16.58 for ; Wed, 25 Oct 2017 19:16:58 -0700 (PDT) Received-SPF: pass (google.com: domain of thiago@macieira.org designates 78.47.120.188 as permitted sender) client-ip=78.47.120.188; Original-Received: from tjmaciei-mobl1.localnet (unknown [IPv6:2601:1c0:4501:5f9f:d45e:bf18:2219:b394]) by gondolin.macieira.info (Postfix) with ESMTPSA id EB70111B5A6 for ; Wed, 25 Oct 2017 19:16:57 -0700 (PDT) In-Reply-To: X-Original-Sender: thiago@macieira.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of thiago@macieira.org designates 78.47.120.188 as permitted sender) smtp.mailfrom=thiago@macieira.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:35106 Archived-At: On Wednesday, 25 October 2017 18:51:43 PDT Nevin Liber wrote: > Technically, it doesn't have to be a breaking change, as long as all it > > does is define behavior for: > > const char s[] = { 'H', 'e', 'l', 'l', 'o' }; > > string_view b(s); > > > > Right now: > > > > b.size() // UB > > I don't see that as particularly useful. QStringView has both a pointer and an array constructor. That means: const char16_t str[] = u"Hello\0World"; QStringView(str).size() == 11 // constexpr QStringView(+str).size() == 5 // not constexpr We've also had a long-time issue with embedded nuls in arrays in other contexts. For example: const char data[] = "Hello World"; QByteArray ba(data); ba[5] = '\0'; return QString::fromLatin1(ba); Previously, QString::fromLatin1 did not have an overload for QByteArray, so it was automatically cast to const char* and strlen applied. So this code returned "Hello". At some point, we added the overload, but it broke a lot of code that depended on the null stopping the conversion. And it wasn't just a handful of cases, plus they were quite difficult to track down. If we had added the constructor at the moment the class was introduced, there would have been no legacy to deal with. Now there will be, so it needs to be done with great care. -- Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Software Architect - Intel Open Source Technology Center -- 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/5005582.pCRZNEiGFO%40tjmaciei-mobl1. .