220 8694 article Path: news.gmane.org!not-for-mail From: gornishanov@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: string_view::is_null() Date: Sun, 19 Jan 2014 10:31:58 -0800 (PST) Lines: 107 Approved: news@gmane.org Message-ID: 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> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_401_757183.1390156318178" X-Trace: ger.gmane.org 1390156317 27412 80.91.229.3 (19 Jan 2014 18:31:57 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 19 Jan 2014 18:31:57 +0000 (UTC) Cc: gornishanov@gmail.com To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC47RF4IW4GRBH5U6CLAKGQEF4PI43Y@isocpp.org Sun Jan 19 19:32:02 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 1W4xA9-0004wm-AG for gclcip-std-proposals@m.gmane.org; Sun, 19 Jan 2014 19:32:01 +0100 Original-Received: by mail-yk0-f200.google.com with SMTP id 200sf7740045ykr.3 for ; Sun, 19 Jan 2014 10:32:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc: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=CohEz+aE51dhZrCITxjSTkNt7hvHsHaJW8fJyi/eLq8=; b=vjd8BKiz0VYnNXzaK9zHgJToWeHRe0cyjwuYqm5rXF7JkOCR9OAfewiWVwWrilV9p6 46SiVwtQGeLNshQfC9QUGNQLDr1+Dn/c8tfz13KywQutMCkzpkEJyAjbMww9tlo9JiZ7 eW5V40RhWpTb09aVp/SkU0sB7ALHjR+RdIJYF9ufXGj7ba3WtO9tHnxCwIXSij7H8sHI iwa77gTih8DIdXhZZUE1S7uQ04qJ1rIp8xSvJ/0QB3StXLi5YVPOJdEA7OjiVUlY8ZVN Tfm5rcmW85KMriDZn8xNOl8awJsqEF18Ud4tIXBIe0uiHc0dUkcWsegjVXSsjK6TYi3V gv4g== 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:cc: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=CohEz+aE51dhZrCITxjSTkNt7hvHsHaJW8fJyi/eLq8=; b=m9ETij4B4xCcV6cXlz8ZPbEsTim1fhy/y4RFCwsE/0yr2Plfq1DL8nNIy/wrOOGUzY 4Iz2sK835ySXeG/kDF/zSE63hZekoCltY4SOzkI9Av28xh8WgrHGR7H+atxrAUtRRFsv 1DUL7kGxDitTXw0y59VHjEjnRjREbss3O+Zm2c04uQsQP4eku9AM6I9cmCdaK2LC7LWB oOJRytIuzvH7vBpb/SjFtq0HI9XQojda0idABln6jWgahnxLGCc86llsiRchz+SMRHKd 3XjQkHhrUghB8AH2dvoHPRVEpAzTwuRkYjzOC8tCNGxTwDrxK86u/s59Re5lz97OAIAi oW/A== X-Gm-Message-State: ALoCoQmFSTSJx5dAWicVQtzHwQvCH/25QIpvHmNIG51UXYWZiLfS6dN/XjvbPKN9LSNA4vagU3Th X-Received: by 10.52.76.34 with SMTP id h2mr4436789vdw.2.1390156320461; Sun, 19 Jan 2014 10:32:00 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.51.15.229 with SMTP id fr5ls1309456igd.13.canary; Sun, 19 Jan 2014 10:31:59 -0800 (PST) X-Received: by 10.50.111.200 with SMTP id ik8mr173651igb.7.1390156319686; Sun, 19 Jan 2014 10:31:59 -0800 (PST) In-Reply-To: X-Original-Sender: gornishanov@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:8694 Archived-At: ------=_Part_401_757183.1390156318178 Content-Type: text/plain; charset=UTF-8 I did not propose using unspecialized optional. I suggested to add specialization of optional> to string_view header. Thus any use of optional will pick up specialized version that can have constructors that you desire. I think it is beneficial to not to roll nullability into string_view. optional is The Way to make type nullable and where possible, one can use specialized optional to add additional constructors and/or provide more efficient implementation than default optional. On Saturday, January 18, 2014 7:30:17 AM UTC-8, Alexander Bolz wrote: > Am Samstag, 18. Januar 2014 00:10:41 UTC+1 schrieb gorni...@gmail.com: >> >> What if string_view provides a specialization for optional>? >> >> That way optional can be implemented very efficiently by >> checking if sv.begin() == nullptr and does not consume any extra storage. >> An extra benefit is that we have clear distinction between nullable types >> (optional) and regular types, int, vector, string_view, etc. >> >> Will this solution satisfy the original poster? >> > > An (unspecialized) optional is not always an option. E.g. I > can't simply change a function like > > void f(char const* s) {} > > to > > void f(optional s) {} > > because I can no longer write f("hello"). So the specialization should be > implicitly constructible from a char array. > And then an optional constructed from a nullptr should be an > uninitialized optional since there > are no preconditions on f, I should be able to write > f(getenv("not-an-env-var")). > > -- --- 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_401_757183.1390156318178 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
I did not propose using unspecialized optional. I sug= gested to add specialization of optional<basic_string_view<...>>= ; to string_view header. Thus any use of optional<string_view> will p= ick up specialized version that can have constructors that you desire.

I think it is beneficial to not to roll nullability in= to string_view. optional is The Way to make type nullable and where po= ssible, one can use specialized optional to add additional constructors and= /or provide more efficient implementation than default optional.
=

On Saturday, January 18, 2014 7:30:17 AM UTC-8, Alexander Bolz wrot= e:
Am Samstag, 18. Janua= r 2014 00:10:41 UTC+1 schrieb gorni...@gmail.com:
What if string_view provides a specializa= tion for optional<string_view<>>?

That= way optional<string_view> can be implemented very efficiently by che= cking if sv.begin() =3D=3D nullptr and does not consume any extra storage. = An extra benefit is that we have clear distinction between nullable types (= optional<T>) and regular types, int, vector, string_view, etc.
<= div>
Will this solution satisfy the original poster?

An (unspecialized) optional<stri= ng_view> is not always an option. E.g. I can't simply change a func= tion like

void f(char const* s) {}

<= /div>
to

void f(optional<string_view> s)= {}

because I can no longer write f("hello"). So t= he specialization should be implicitly constructible from a char array= ..
And then an optional<string_view> constructed from a null= ptr should be an uninitialized optional since there
are no precon= ditions on f, I should be able to write f(getenv("not-an-env-var")).
<= div>

--
 
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