220 35107 article Path: news.gmane.org!.POSTED!not-for-mail From: Nevin Liber Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Marking more std::string_view members noexcept Date: Wed, 25 Oct 2017 21:30:21 -0500 Lines: 139 Approved: news@gmane.org Message-ID: References: <3d03cd7d-2177-98fd-408d-f74b1f6a8552@gmail.com> <5005582.pCRZNEiGFO@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="001a114b6d0699a48d055c69f69a" X-Trace: blaine.gmane.org 1508985070 31728 195.159.176.226 (26 Oct 2017 02:31:10 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 26 Oct 2017 02:31:10 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBCE35H5S6IDBBZ4RYXHQKGQETAV22MQ@isocpp.org Thu Oct 26 04:31:03 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f70.google.com ([209.85.213.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1e7Xwf-0006wL-KN for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id p42sor1743456uad.108.2017.10.25.19.31.02 for (Google Transport Security); Wed, 25 Oct 2017 19:31:02 -0700 (PDT) Received-SPF: pass (google.com: domain of nliber@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.159.41.65 with SMTP id t59mr2852628uat.99.1508985062137; Wed, 25 Oct 2017 19:31:02 -0700 (PDT) Original-Sender: nliber@gmail.com Original-Received: by 10.103.71.140 with HTTP; Wed, 25 Oct 2017 19:30:21 -0700 (PDT) In-Reply-To: <5005582.pCRZNEiGFO@tjmaciei-mobl1> X-Original-Sender: nevin@eviloverlord.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=PRQVcFbr; spf=pass (google.com: domain of nliber@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=nliber@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:35107 Archived-At: --001a114b6d0699a48d055c69f69a Content-Type: text/plain; charset="UTF-8" On Wed, Oct 25, 2017 at 9:16 PM, Thiago Macieira wrote: > 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 > I'm not sure what constexpr has to do with it. Isn't it array vs. pointer that matters? It also means QStringView(b ? u"Hello\0World" : u"Howdy\0World") has subtly different behavior than QStringView(b ? u"Hello\0World" : u"Goodbye\0World"), doesn't it? > 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. > Again, I think matching an array is the wrong solution to the question of "is this a string literal"? A better solution might be a magic type that, in template contexts, matches better than an array but easily decays to an array. OTOH, it might not be (I haven't really thought about it much). And it still wouldn't address the ternary operator problem I mentioned above. -- Nevin ":-)" Liber +1-847-691-1404 <(847)%20691-1404> -- 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/CAGg_6%2BM1gvNh82YX6x4Nr3%3DrFSPW973nmumTF0SkyMJ7c2Yoew%40mail.gmail.com. --001a114b6d0699a48d055c69f69a Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Wed, Oct 25, 2017 at 9:16 PM, Thiago Macieira <thiag= o@macieira.org> wrote:
On Wednesday, 25 Oc= tober 2017 18:51:43 PDT Nevin Liber wrote:
> Technically, it doesn't have to be a breaking change, as long as a= ll it
>
> does is define behavior for:
> > const char s[] =3D { '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:=

=C2=A0 =C2=A0 =C2=A0 =C2=A0 const char16_t str[] =3D u"Hello\0World&qu= ot;;

=C2=A0 =C2=A0 =C2=A0 =C2=A0 QStringView(str).size() =3D=3D 11=C2=A0 =C2=A0/= / constexpr
=C2=A0 =C2=A0 =C2=A0 =C2=A0 QStringView(+str).size() =3D=3D 5=C2=A0 =C2=A0/= / not constexpr

I'm not sure what c= onstexpr has to do with it.=C2=A0 Isn't it array vs. pointer that matte= rs?

It also means

QString= View(b ? u"Hello\0World" : u"Howdy\0World") has subtly = different behavior than QStringView(b ? u"Hello\0World" : u"= Goodbye\0World"), doesn't it?
=C2=A0
If we had added the constructor at the moment the class was introduced, the= re
would have been no legacy to deal with. Now there will be, so it needs to b= e
done with great care.

Again, I think ma= tching an array is the wrong solution to the question of "is this a st= ring literal"?

A better solution might be a m= agic type that, in template contexts, matches better than an array but easi= ly decays to an array.=C2=A0 OTOH, it might not be (I haven't really th= ought about it much).=C2=A0 And it still wouldn't address the ternary o= perator problem I mentioned above.
--
=C2=A0Nevin ":= -)" Liber=C2=A0 <mailto:nevin@eviloverlord.com> =C2=A0+1-847-691-1404

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