220 28422 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: Tue, 27 Sep 2016 12:47:13 -0500 Lines: 113 Approved: news@gmane.org Message-ID: 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: multipart/alternative; boundary=001a113d2f5214b208053d80d887 X-Trace: blaine.gmane.org 1474998495 3504 195.159.176.226 (27 Sep 2016 17:48:15 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 27 Sep 2016 17:48:15 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBCE35H5S6IDBBSXBVK7QKGQEIHMQ64I@isocpp.org Tue Sep 27 19:48:11 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f199.google.com ([209.85.161.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bowU2-0007L3-1h for gclcip-std-proposals@m.gmane.org; Tue, 27 Sep 2016 19:47:58 +0200 Original-Received: by mail-yw0-f199.google.com with SMTP id y201sf12575643ywg.3 for ; Tue, 27 Sep 2016 10:48:00 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=O6BxmvkS+ZYxO0KhIcdROf/in7J+Nr7l0LjqkcIocmA=; b=dR+L/jeblpm3mv2ryENEmc0Z2tJ+tzvRQCXsfU2xAQfIZqQl2t/uYWMXXocGHlu8OB hU9a1OaLa6iPmoI5CzjCjAArlU3Ak5V6TRI5iOnf4FjgJntVzAdSY2uxtpfSrKxD0LbE GX8DEuXVv77EjSFK7GWhmhOTSMI0Wq/F+uPp831mXd9YHWGB5+b+IL1PqWEN9dYb1ZxY zHD39vYgAfLScw3Cl2xcXrMhdAHwS7gmT+ukzrAF5ArjRAxYxL5Ti7/gfM2/3c5sx02p mpZILFyiaNfMx/UVRlKm4lJgafarCRVUh/xe1aCytBhqukCNIjrPnJSl370YrTBXLek7 DxUw== X-Gm-Message-State: AE9vXwPOtBcKVMU7nUsZaHvbREwXAW1yzgVb+PlX1QlkuFrmCOY5/HToJuD1TlrNxzB9hg== X-Received: by 10.129.37.11 with SMTP id l11mr7616491ywl.165.1474998479660; Tue, 27 Sep 2016 10:47:59 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.134.205 with SMTP id q74ls133857ioi.47.gmail; Tue, 27 Sep 2016 10:47:54 -0700 (PDT) X-Received: by 10.107.13.212 with SMTP id 203mr29570720ion.178.1474998474330; Tue, 27 Sep 2016 10:47:54 -0700 (PDT) Original-Received: from mail-oi0-x22a.google.com (mail-oi0-x22a.google.com. [2607:f8b0:4003:c06::22a]) by mx.google.com with ESMTPS id 98si2299004oti.263.2016.09.27.10.47.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Sep 2016 10:47:54 -0700 (PDT) Received-SPF: pass (google.com: domain of nliber@gmail.com designates 2607:f8b0:4003:c06::22a as permitted sender) client-ip=2607:f8b0:4003:c06::22a; Original-Received: by mail-oi0-x22a.google.com with SMTP id t83so24155045oie.3 for ; Tue, 27 Sep 2016 10:47:54 -0700 (PDT) X-Received: by 10.202.237.143 with SMTP id l137mr36431847oih.121.1474998473882; Tue, 27 Sep 2016 10:47:53 -0700 (PDT) Original-Sender: nliber@gmail.com Original-Received: by 10.157.1.237 with HTTP; Tue, 27 Sep 2016 10:47:13 -0700 (PDT) In-Reply-To: <3d03cd7d-2177-98fd-408d-f74b1f6a8552@gmail.com> X-Original-Sender: nevin@eviloverlord.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of nliber@gmail.com designates 2607:f8b0:4003:c06::22a 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:28422 Archived-At: --001a113d2f5214b208053d80d887 Content-Type: text/plain; charset=UTF-8 On Tue, Sep 27, 2016 at 7:21 AM, Andrey Semashev wrote: > Hi, > > I'm looking at string_view interface definition in N4606 and wondering why > so many members are not marked noexcept? For example, these constructors: > > constexpr basic_string_view(const charT* str); > constexpr basic_string_view(const charT* str, size_type len); > > Assuming that the input string is not a constant expression, the first > constructor would call an equivalent of strlen(str), which in 99% is a > no-throw operation. Why not mark it "noexcept(noexcept(traits::length(str))"? > The second constructor does not even need that and could be simply noexcept. > > I'm most interested in constructors, but other members like operator[], > front(), back(), substr(), compare() also don't seem to need to ever throw, > yet they are not marked noexcept. > Is there a reason for these omissions? > The usual reason: they are narrow contracts with preconditions. See n3279 . > Also, why there is no obvious constructor from basic_string? > See p0254r2 . Note: you can still construct a basic_string_view from a basic_string via basic_string::operator basic_string_view. -- Nevin ":-)" Liber +1-847-691-1404 -- 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%2BPEcOT0tdSBEkZRxDWB%2BKoEtkq2DJA_3hu7DgUeTU7M8w%40mail.gmail.com. --001a113d2f5214b208053d80d887 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Tue, Sep 27, 2016 at 7:21 AM, Andrey Semashev <andrey.semashev@gmail.com> wrote:
Hi,

I'm looking at string_view interface definition in N4606 and wondering = why so many members are not marked noexcept? For example, these constructor= s:

=C2=A0 constexpr basic_string_view(const charT* str);
=C2=A0 constexpr basic_string_view(const charT* str, size_type len);

Assuming that the input string is not a constant expression, the first cons= tructor would call an equivalent of strlen(str), which in 99% is a no-throw= operation. Why not mark it "noexcept(noexcept(traits::length(str= ))"? The second constructor does not even need that and could be simpl= y noexcept.

I'm most interested in constructors, but other members like operator[],= front(), back(), substr(), compare() also don't seem to need to ever t= hrow, yet they are not marked noexcept.=C2=A0

Is there a reason for these omissions?

= The usual reason: =C2=A0they are narrow contracts with preconditions.=C2=A0= See=C2=A0n3279.
=C2=A0
p0254r2.=C2=A0 Note: =C2=A0you can sti= ll construct a basic_string_view= from a basic_string via basic_string::operator basic_string_view.=C2=A0
--
=C2=A0Nevin &= quot;:-)" Liber=C2=A0 <mailto:nevin@eviloverlord.com> =C2=A0+1-847-691-1404=

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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%2BPEcO= T0tdSBEkZRxDWB%2BKoEtkq2DJA_3hu7DgUeTU7M8w%40mail.gmail.com.
--001a113d2f5214b208053d80d887-- .