220 33124 article Path: news.gmane.org!.POSTED!not-for-mail From: "'Matt Calabrese' via ISO C++ Standard - Future Proposals" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: std::optional - support for sentinel values Date: Wed, 5 Jul 2017 10:24:24 -0400 Lines: 70 Approved: news@gmane.org Message-ID: References: <6e23864f-827a-4bdb-89de-a60d8f5be993@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="94eb2c049632d2168f055392c11c" X-Trace: blaine.gmane.org 1499264670 11307 195.159.176.226 (5 Jul 2017 14:24:30 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 5 Jul 2017 14:24:30 +0000 (UTC) To: "ISO C++ Standard - Future Proposals" Original-X-From: std-proposals+bncBCGNLO5F34OBBGXN6PFAKGQEN6UJDKI@isocpp.org Wed Jul 05 16:24:25 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f198.google.com ([209.85.217.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dSlE6-0002Xh-Kq for gclcip-std-proposals@m.gmane.org; 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[2607:f8b0:4001:c0b::22a]) by mx.google.com with ESMTPS id n26si20736215ioe.134.2017.07.05.07.24.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 05 Jul 2017 07:24:26 -0700 (PDT) Received-SPF: pass (google.com: domain of calabrese@google.com designates 2607:f8b0:4001:c0b::22a as permitted sender) client-ip=2607:f8b0:4001:c0b::22a; Original-Received: by mail-it0-x22a.google.com with SMTP id k192so86927889ith.1 for ; Wed, 05 Jul 2017 07:24:26 -0700 (PDT) X-Received: by 10.36.160.8 with SMTP id o8mr40211985ite.10.1499264665633; Wed, 05 Jul 2017 07:24:25 -0700 (PDT) Original-Received: by 10.107.3.18 with HTTP; Wed, 5 Jul 2017 07:24:24 -0700 (PDT) In-Reply-To: X-Original-Sender: calabrese@google.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.b=AJIJRXT5; spf=pass (google.com: domain of calabrese@google.com designates 2607:f8b0:4001:c0b::22a as permitted sender) smtp.mailfrom=calabrese@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com X-Original-From: Matt Calabrese 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:33124 Archived-At: --94eb2c049632d2168f055392c11c Content-Type: text/plain; charset="UTF-8" On Thu, Jun 29, 2017 at 7:05 PM, Arthur O'Dwyer wrote: > The other extension, orthogonal to first one, is to allow value to be >> stored using alternate representation. As an example, reference type can be >> stored as a pointer and simply presented as reference. This will also allow >> to have cheap and relatively easy support for storing references in >> std::optional, without need of completely separate type specialization. >> > > This is optional>. > As for why optional is a terrible, horrible, no-good, very bad idea, > please see Matt Calabrese's talk > from C++Now. > Erm, that's not what I said in my talk. In fact, quite the opposite. I advocate support for optional -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CANh8DEkc-u4-60q121uG7moPVHBuAcQJTjpM2Bo9kXx%3Dxn4KYQ%40mail.gmail.com. --94eb2c049632d2168f055392c11c Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On T= hu, Jun 29, 2017 at 7:05 PM, Arthur O'Dwyer <arthur.j.odwyer@g= mail.com> wrote:

The other extension, orthogonal to first one, is to allow value= to be stored using alternate representation. As an example, reference type= can be stored as a pointer and simply presented as reference. This will al= so allow to have cheap and relatively easy support for storing references i= n std::optional, without need of completely separate type specialization.


This is optional<ref= erence_wrapper<T>>.
As for why optional<T&&g= t; is a terrible, horrible, no-good, very bad idea, please see Matt Calabr= ese's talk from C++Now.

Erm, that's not what I said in my talk. In fact, quite the opposite. I= advocate support for optional<T&>=C2=A0

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