220 7040 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 22:30:10 +0300 Lines: 91 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=001a11c25b4881dde504e8037292 X-Trace: ger.gmane.org 1381001408 28381 80.91.229.3 (5 Oct 2013 19:30:08 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 5 Oct 2013 19:30:08 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC5JHI7A7ALRBQWRYGJAKGQEOV3CJKQ@isocpp.org Sat Oct 05 21:30:12 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wg0-f70.google.com ([74.125.82.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1VSXYJ-0001e1-OV for gclcip-std-proposals@m.gmane.org; Sat, 05 Oct 2013 21:30:11 +0200 Original-Received: by mail-wg0-f70.google.com with SMTP id m15sf6830849wgh.5 for ; Sat, 05 Oct 2013 12:30:11 -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=rHDSDisLZzdGUNg4Q9OzI8AozonPa08OcWgct5mVneY=; b=Bz3hB5WGvOrHA91CMbd2CmgytI4oqhcmrBnBRcEZ5JjHgrd4AqUurxdOpHI+phnV45 1u3pyNZHVQqpzZOVW/g1Euv7kZOMlcA0KRmrqJ216NcYKq/X3sSLodl86voTp7F7vVDV AyyI2ievshEYxIWuoqxbUEK88rSvRavxkrnQfi+vR0kQihKRkyQs/Cl/1jjd7m4RKjUE xqsKlWhKCdeDImL8TsIvzNj7C3hndaNDCEEJ3sW/ysM4Ne4w+AvEQYr4In56tjAjhQOI gHR6hExJo3iwWtSHv9QdHKJBrxB9GguGlgI0me/sCaduFNQFmvym5hypbiDehXEcnqW5 TJNQ== X-Received: by 10.180.109.19 with SMTP id ho19mr5869695wib.7.1381001411267; Sat, 05 Oct 2013 12:30:11 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.88.39 with SMTP id bd7ls574719wib.47.canary; Sat, 05 Oct 2013 12:30:10 -0700 (PDT) X-Received: by 10.180.10.8 with SMTP id e8mr12429852wib.65.1381001410600; Sat, 05 Oct 2013 12:30:10 -0700 (PDT) Original-Received: from mail-wi0-x233.google.com (mail-wi0-x233.google.com [2a00:1450:400c:c05::233]) by mx.google.com with ESMTPS id w2si8004087wjz.136.1969.12.31.16.00.00 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sat, 05 Oct 2013 12:30:10 -0700 (PDT) Received-SPF: pass (google.com: domain of ville.voutilainen@gmail.com designates 2a00:1450:400c:c05::233 as permitted sender) client-ip=2a00:1450:400c:c05::233; Original-Received: by mail-wi0-f179.google.com with SMTP id hm2so3141221wib.6 for ; Sat, 05 Oct 2013 12:30:10 -0700 (PDT) X-Received: by 10.180.11.37 with SMTP id n5mr12293233wib.25.1381001410500; Sat, 05 Oct 2013 12:30:10 -0700 (PDT) Original-Received: by 10.194.42.70 with HTTP; Sat, 5 Oct 2013 12:30:10 -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:c05::233 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:7040 Archived-At: --001a11c25b4881dde504e8037292 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 5 October 2013 22:05, Andrzej Krzemie=C5=84ski wrot= e: > > Oh, you spotted a different problem than I did. Mine was that (even if I > fixed yours) it is not clear how to handle a case where *T* has a > constructor taking another optional. Consider a more tricky type: > > * struct Port > { > * > * Port (optional oi); > Port (int); > }; > * > > And now the code that uses it: > > > * optional oi; > ** optional op =3D oi;* > > Now, forget how optional is or might be implemented. As a user, which > constructor of *Port *would you expect to be called? > > The one taking optional, since optional doesn't automatically convert to an int. If you have int i; optional op =3D i; then I expect Port(int) to be used. --=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/. --001a11c25b4881dde504e8037292 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable



On 5 October 2013 22:05, Andrzej Krzemie=C5=84ski <akrzemi1@gmail= ..com> wrote:

Oh, you spotted a = different problem than I did. Mine was that (even if I fixed yours) it is n= ot clear how to handle a case where T has a constructor taking anoth= er optional. Consider a more tricky type:

=C2=A0 struct Port
=C2=A0 {
=C2=A0=C2=A0=C2=A0 Por= t (optional<int> oi);
=C2=A0=C2=A0=C2=A0 Port (int);
=C2=A0 };

And now the code that uses it:


=C2=A0 optional<int> oi;
=C2=A0 optional<Por= t> op =3D oi;

Now, forget how optional is or might be i= mplemented. As a user, which constructor of Port would you expect to= be called?


The one taking optional<= ;int>, since optional doesn't automatically convert to an int. If yo= u
have
int i;
optional<Port> op =3D i;=
then I expect Port(int) to be used.

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