220 7037 article Path: news.gmane.org!not-for-mail From: Ville Voutilainen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: More converting constructors for Optional Date: Sat, 5 Oct 2013 21:57:50 +0300 Lines: 93 Approved: news@gmane.org Message-ID: References: <417ebcd9-ff0b-49d8-b055-bd098e97dddc@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a11c227e8e0f9c204e802fed7 X-Trace: ger.gmane.org 1380999468 9122 80.91.229.3 (5 Oct 2013 18:57:48 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 5 Oct 2013 18:57:48 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC5JHI7A7ALRBLWCYGJAKGQE3XUZLHQ@isocpp.org Sat Oct 05 20:57:52 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ea0-f199.google.com ([209.85.215.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1VSX31-0007sw-Ql for gclcip-std-proposals@m.gmane.org; Sat, 05 Oct 2013 20:57:51 +0200 Original-Received: by mail-ea0-f199.google.com with SMTP id r16sf6676077ead.10 for ; Sat, 05 Oct 2013 11:57:51 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=fWY09uUTnIlZNlEdU52QjzSE3s2YspZHtjaWwo+UdPQ=; b=d8vkIrcz1WeME4+r9pPqdgNhsSklBSodm/6nqfKkQmgv5j4ImIODULihMwxLaYMkIT e6gLXFDCwLVz6lozpwpxE8YQisWpPrU9cPTbpIzM9qxLCK32Uu54LcyEhHLx4617x3JL RKR9m8ZS8nUiuyonAoF7a/Hoo6U8b3HbMQTAYudlfLBYvD0qcnWyIrV1pVl67zrz3i9n HQdD+PSbKD7US1ZwkQxpwzblLA9q6yicH3xJP7IOK/Q0gswYzAGlolj/4NuCBGuzwFJg mWsIL7s+ujkZKNrBEMaW+62KW6b7wTY7I4v3gAjnmuuLjkfUKcPuT6+cJ6+mrALdfvzj ZMBA== X-Received: by 10.180.149.135 with SMTP id ua7mr5841722wib.0.1380999471241; Sat, 05 Oct 2013 11:57:51 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.14.227 with SMTP id s3ls574923wic.50.canary; Sat, 05 Oct 2013 11:57:50 -0700 (PDT) X-Received: by 10.194.93.105 with SMTP id ct9mr17713731wjb.6.1380999470668; Sat, 05 Oct 2013 11:57:50 -0700 (PDT) Original-Received: from mail-we0-x22b.google.com (mail-we0-x22b.google.com [2a00:1450:400c:c03::22b]) by mx.google.com with ESMTPS id gd10si4919979wic.44.1969.12.31.16.00.00 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sat, 05 Oct 2013 11:57:50 -0700 (PDT) Received-SPF: pass (google.com: domain of ville.voutilainen@gmail.com designates 2a00:1450:400c:c03::22b as permitted sender) client-ip=2a00:1450:400c:c03::22b; Original-Received: by mail-we0-f171.google.com with SMTP id p61so6282077wes.30 for ; Sat, 05 Oct 2013 11:57:50 -0700 (PDT) X-Received: by 10.180.13.174 with SMTP id i14mr12454831wic.49.1380999470576; Sat, 05 Oct 2013 11:57:50 -0700 (PDT) Original-Received: by 10.194.42.70 with HTTP; Sat, 5 Oct 2013 11:57:50 -0700 (PDT) In-Reply-To: X-Original-Sender: ville.voutilainen@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of ville.voutilainen@gmail.com designates 2a00:1450:400c:c03::22b as permitted sender) smtp.mail=ville.voutilainen@gmail.com; dkim=pass header.i=@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:7037 Archived-At: --001a11c227e8e0f9c204e802fed7 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 5 October 2013 21:55, Zhihao Yuan wrote: > On Sat, Oct 5, 2013 at 1:14 PM, Andrzej Krzemie=C5=84ski > wrote: > > Hi Everyone, > > It was suggested by LEWG that the following converting constructor > should be > > added to optional: > > > > optional os =3D "str"; > > optional> op =3D unique_ptr{}; > > > > and probably also this should work: > > > > optional> op =3D optional>{}; > > I don't expect these to work. Within the optional > domain, we know T -> optional is safe; but > outside this domain, it does not seem to be a good > idea to judge which kind of conversion is safe with > optional instead of just take the decision of C++. > > > Well, the LEWG guidance to explore these conversions was clear. --=20 ---=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. --001a11c227e8e0f9c204e802fed7 Content-Type: text/html; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable



On 5 October 2013 21:55, Zhihao Yuan <zy@miator.net> wr= ote:
On Sat, Oct 5, 2013 at 1:14 PM, Andrzej Krzemie=F1ski <= ;akrzemi1@gmail.com> wrote: > Hi Everyone,
> It was suggested by LEWG that the following converting constructor sho= uld be
> added to optional:
>
> =A0 optional<string> os =3D "str";
> =A0 optional<unique_ptr<Base>> op =3D unique_ptr<Derive= d>{};
>
> and probably also this should work:
>
> =A0 optional<unique_ptr<Base>> op =3D optional<unique_p= tr<Derived>>{};

I don't expect these to work. =A0Within the optional
domain, we know T -> optional<T> is safe; but
outside this domain, it does not seem to be a good
idea to judge which kind of conversion is safe with
optional instead of just take the decision of C++.



Well, the LEWG guidance to explore these convers= ions was clear.

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