220 28423 article Path: news.gmane.org!.POSTED!not-for-mail From: Andrey Semashev Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Marking more std::string_view members noexcept Date: Tue, 27 Sep 2016 21:24:44 +0300 Lines: 55 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: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1475000700 20065 195.159.176.226 (27 Sep 2016 18:25:00 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 27 Sep 2016 18:25:00 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCXY5TXHWYJRB3XSVK7QKGQELTBD7PI@isocpp.org Tue Sep 27 20:24:56 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f72.google.com ([74.125.82.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1box3e-0003p9-FZ for gclcip-std-proposals@m.gmane.org; Tue, 27 Sep 2016 20:24:46 +0200 Original-Received: by mail-wm0-f72.google.com with SMTP id w84sf16160676wmg.1 for ; Tue, 27 Sep 2016 11:24:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-transfer-encoding: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=t9EkczRL7nL8gIxsuK5PUktv0GoiRZwHStYvyUA1J9Y=; b=KJul57Dqny7Da8c6yiBBQiNZf9xEESPBa6rMr8VMkKiomNShosuPzXeihyUb1QGPiQ FokH4zTsknVJIICKE81BWC5cw960Gmk+0TMb8LSjoPl0LRa5GCQmubN6VGUWzQ24ZUrL PSQiUP7DxeoB3q+b9fD341DSq3G8XzGmUGDskoEfW2cBaTc2kSSWbr4m4DJkok0hr1ro y/1SNU1r6XLe5/C4QDrahXGM5gld1CQcYy7NQlPBb0DPK+GBdS0XqQGMqfRZYs6sGUto ighnBsin0so3VmSvfHR7dkeZlyR6IBw1QUpzavuW/vz97NFcXFEFxKpgPpJjRGTvjdav X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :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=t9EkczRL7nL8gIxsuK5PUktv0GoiRZwHStYvyUA1J9Y=; b=FfUaS1C39QT8pLDtOcfcLcXJvMmYrfrj8Yf/wxDkW/7idhXE5y+3TLwGfzRwzw86lq gU7WDjvnafOzFv/FgDn5jZO0F5EcPpBWxxO6VvPjq3OAYzQzKIve5UyLOy9aPN3PQYzF Eqi73k6DdwZlzhWF5nE91lMvC9HT6F2E5xpdVWNmQhGt3AGTQ3qw6NeBFBImTLKPZh+7 t6fCprorlrC5/Ja6pOP4hFfbv80XyGt9viwbhxT553nOjEgIUt9YTsuxXYqAN7NexvRy kv77x9+2h2diV6Z2fkdwk6vzCSr+Xe6Npl3RZTIWOnOZrkuGKV5Ft8ntL1PITGrkgVmL X-Gm-Message-State: AA6/9Rk+R6oLN8ljbR6LOYwZmf8YsWycJROD61xmufiyE92K+ndB9M57BDhyFVUnFIA1Qw== X-Received: by 10.28.208.141 with SMTP id h135mr343541wmg.3.1475000687865; Tue, 27 Sep 2016 11:24:47 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.25.25.206 with SMTP id 197ls622102lfz.13.gmail; Tue, 27 Sep 2016 11:24:46 -0700 (PDT) X-Received: by 10.46.33.77 with SMTP id h74mr6993349ljh.57.1475000686202; Tue, 27 Sep 2016 11:24:46 -0700 (PDT) Original-Received: from mail-lf0-x22b.google.com (mail-lf0-x22b.google.com. [2a00:1450:4010:c07::22b]) by mx.google.com with ESMTPS id k80si763082lfi.216.2016.09.27.11.24.46 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Sep 2016 11:24:46 -0700 (PDT) Received-SPF: pass (google.com: domain of andrey.semashev@gmail.com designates 2a00:1450:4010:c07::22b as permitted sender) client-ip=2a00:1450:4010:c07::22b; Original-Received: by mail-lf0-x22b.google.com with SMTP id l131so31894695lfl.2 for ; Tue, 27 Sep 2016 11:24:46 -0700 (PDT) X-Received: by 10.46.32.5 with SMTP id g5mr1152464ljg.55.1475000685510; Tue, 27 Sep 2016 11:24:45 -0700 (PDT) Original-Received: from [192.168.1.2] (broadband-90-154-68-136.nationalcablenetworks.ru. [90.154.68.136]) by smtp.googlemail.com with ESMTPSA id z139sm640077lff.16.2016.09.27.11.24.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Sep 2016 11:24:44 -0700 (PDT) In-Reply-To: X-Original-Sender: andrey.semashev@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of andrey.semashev@gmail.com designates 2a00:1450:4010:c07::22b as permitted sender) smtp.mailfrom=andrey.semashev@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:28423 Archived-At: On 09/27/16 20:47, Daniel Kr=C3=BCgler wrote: > 2016-09-27 14:21 GMT+02:00 Andrey Semashev : >> Hi, >> >> I'm looking at string_view interface definition in N4606 and wondering w= hy >> 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 no= t >> 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 thr= ow, >> yet they are not marked noexcept. >> >> Is there a reason for these omissions? > > This is so, because these functions have a narrow contract. The > current guideline for LWG was described by this proposal: > > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3279.pdf I see. Still, it feels wrong that functions that you never expect to=20 throw are not marked noexcept. When you write non-throwing code you=20 would look at the functions your code calls and not seeing noexcept=20 there immediately throws a red flag. >> Also, why there is no obvious constructor from basic_string? > > Which one in particular is in your mind? I was thinking of "basic_string_view(basic_string const&)", but Nevin=20 already pointed me to p0254r2 and I can see there is a conversion=20 operator in basic_string instead. This looks like a very reasonable=20 solution. --=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/af89c375-0437-4092-cfc7-d93eafbf969e%40gmail.com= .. .