220 8717 <975e038a-8ae2-48d4-ba5b-3b6d7d67cea7@isocpp.org> article Path: news.gmane.org!not-for-mail From: Alexander Bolz Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: string_view::is_null() Date: Sun, 19 Jan 2014 16:35:11 -0800 (PST) Lines: 164 Approved: news@gmane.org Message-ID: <975e038a-8ae2-48d4-ba5b-3b6d7d67cea7@isocpp.org> References: <8045a4d2-721d-4725-8bb7-7a91b6f53ec8@isocpp.org> <186E0927-C962-4E34-AED0-E7509DD1F0A0@gmail.com> <7aad44d8-6b4e-438a-b309-bd898b994b34@isocpp.org> <9C2C439F-7983-4224-B272-53CAD0E2E456@gmail.com> <8E74B747-7450-41E0-8D1E-48C2D6F81535@gmail.com> <3a3d55c0-20cb-40ff-ae46-84663d21f44d@isocpp.org> <53d0e0c3-7eee-4853-886d-624bf4b22fb4@isocpp.org> <52DC3ED7.90707 07@knejp.de> <52DC5781.2070908@knejp.de> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_1440_13224426.1390178111886" X-Trace: ger.gmane.org 1390178107 24119 80.91.229.3 (20 Jan 2014 00:35:07 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 20 Jan 2014 00:35:07 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCAJPLFFWYPBBQG66GLAKGQE4SSO3KY@isocpp.org Mon Jan 20 01:35:14 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yk0-f200.google.com ([209.85.160.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1W52pe-0004H0-D7 for gclcip-std-proposals@m.gmane.org; Mon, 20 Jan 2014 01:35:14 +0100 Original-Received: by mail-yk0-f200.google.com with SMTP id 200sf8497005ykr.3 for ; Sun, 19 Jan 2014 16:35:13 -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=A5g+bYYeDmuJGr0HhHvTGMf+F1CwgA27kk2j4fHVU8k=; b=RFkUScrcZPrXK995/uFPNuVZEq0qIDQfA8r9XtWR+opVMWOUeHAEaHE1g80kclDInZ /PU/7BQSbkaBpHvDCpqEoBTrNvg3a0KlTREw1fuVKThjVggwh0t4syilK9YLR+4QmMxe DwXix6SpbC0H2MhOoEObXTPH8NfM1U1dk3wzHNTHTJglznu0l9ER81E8kYlB5CtN1OKW EEtrGQEjRKd5N2tFnblalMmRcY1GaWlHOew9BZJgI8eOjob41IrSRRFWMsfOvOVy5YT+ wBiSQ9aRWyZkYw7WJOrOmi4vDnbtxly01w9szyHpm9M1g1ujDP3x6CQp5YVo5j2Pl/MU mkog== 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=A5g+bYYeDmuJGr0HhHvTGMf+F1CwgA27kk2j4fHVU8k=; b=f94aP9lLK6j/vhYnmplvtgIJ29zCnEF3FPm8omQfgEj6TcJJg688XZoA8y7AjLECHl jnhItYlWblIPtr/fggf+xdC69xf21YUJXOIZSEZroDNPV5CGOKuBicBP+ghVMSPX8OQM bmqRRN7ZwKEKrjUg3rd1CTto1gJZ1Ezcd4AZ/wQqGa+JVLfCIyYm+QQvDX9eX4ajlJKA EMGKEXKCjT8HysJiJLzEA3nfKcy4XiAOQw6Qw8O+4OWC4fEZ7h90gdWFhd5NTbEZmpng kObcA2Lc0wYRhQpaPPspLBCoRKpUdmkG6QOMVD0jtDHQ65VUoT2+8afqlRDXjiJBCE69 j6Zw== X-Gm-Message-State: ALoCoQko+A6pb/hGY7EjdVYT2KJxKTyUeFtHPlxZU4JVep8U2Q4AELXxOqxJqR8A6rgHULNMIZE2 X-Received: by 10.58.46.204 with SMTP id x12mr5676999vem.19.1390178113215; Sun, 19 Jan 2014 16:35:13 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.106.102 with SMTP id gt6ls1682497qeb.78.gmail; Sun, 19 Jan 2014 16:35:12 -0800 (PST) X-Received: by 10.140.43.227 with SMTP id e90mr300097qga.4.1390178112775; Sun, 19 Jan 2014 16:35:12 -0800 (PST) In-Reply-To: <52DC5781.2070908@knejp.de> X-Original-Sender: abolz.lists@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:8717 Archived-At: ------=_Part_1440_13224426.1390178111886 Content-Type: text/plain; charset=UTF-8 Am Sonntag, 19. Januar 2014 23:53:53 UTC+1 schrieb Miro Knejp: > > I just don't want to do that. I have a function like > > void f(char const* s) { > if (s == nullptr) > dothis(); > else > dothat(); > } > > and I want to replace char const* with string_view to make it accept a > std::string so I can save some std::string.c_str() > calls. > > Saving some string.c_str() calls isn't a very convincing argument. Not > for me at least. When I have to chose between safety/robustness or > convenience the former wins. Knowing a std::string_view cannot be null just > as std::string cannot be is a valuable quality of life improvement. I would > assume the number of times one needs a nullable string is only a fraction > of the actual uses of string_view. > > string_view has as far as I can remember always been described as a > drop-in replacement for string. Discussing the possibility of a nullable > std::string_view should equally raise a discussion about the possibility of > a nullable std::string. If it is not possible to replace functions taking > (const string&) with (string_view) and have the same semantics it's far > less usefull and only works against the trend of making things safer and > more intuitive. (const char*) methods should always ring alarm bells. > For a function like void print(string const& s) { } there is an implicit precondition: a string can not be constructed from a nullptr. So you have to check this before calling. When replacing string const& with string_view, you just need to make the precondition explicit. Then in both cases data() != null. If you use string.data(), you can't simply replace func(string const&) with func(string_view) even if data() returns non-null, since data() might not be null terminated. void print(string const& s) { printf("%s", s.data()); } If yyou don't use data() then, well... its not important if data() returns nullptr or not. -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_1440_13224426.1390178111886 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Am Sonntag, 19. Januar 2014 23:53:53 UTC+1 schrieb Miro Kn= ejp:
=20 =20 =20
=20

I just don't want to do that. I have a function like

void f(char const* s) {
  if (s =3D=3D nullptr)
    dothis(= );
  else
    dothat();
}

and I want to replace char const* with string_view to make it accept a std::string so I can save some std::string.c_str()
calls.<= /div>
Saving some string.c_str() calls isn't a very convincing argument. Not for me at least. When I have to chose between safety/robustness or convenience the former wins. Knowing a std::string_view cannot be null just as std::string cannot be is a valuable quality of life improvement. I would assume the number of times one needs a nullable string is only a fraction of the actual uses of string_view.

string_view has as far as I can remember always been described as a drop-in replacement for string. Discussing the possibility of a nullable std::string_view should equally raise a discussion about the possibility of a nullable std::string. If it is not possible to replace functions taking (const string&) with (string_view) and have the same semantics it's far less usefull and only works against the trend of making things safer and more intuitive. (const char*) methods should always ring alarm bells.

=
For a function like

void print(string const& s) {
<= font face=3D"courier new, monospace">}

ther= e is an implicit precondition: a string can not be constructed from a nullp= tr.
So you have to check this before calling. When replacing stri= ng const& with string_view,
you just need to make the precond= ition explicit. Then in both cases data() !=3D null.

If you use string.data(), you can't simply replace func(string const&= ;) with func(string_view)
even if data() returns non-null, since = data() might not be null terminated.

void print(string const& s) {
  printf("%s", s.data());
}

If yyou don't use data() then, well... its not important if data()= returns nullptr or not.

--
 
---
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-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-proposals/<= /a>.
------=_Part_1440_13224426.1390178111886-- .