220 2759 <3534ECE0-D67E-443E-9593-76B644FDDF6A@gmail.com> article Path: news.gmane.org!not-for-mail From: Sean Parent Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: optional references -- take 2 Date: Wed, 6 Feb 2013 18:11:37 -0800 Lines: 128 Approved: news@gmane.org Message-ID: <3534ECE0-D67E-443E-9593-76B644FDDF6A@gmail.com> References: <8d57e9e9-e4cc-441c-abeb-e6526531fad5@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (1.0) Content-Type: multipart/alternative; boundary=Apple-Mail-F27E2A10-94FA-48C8-910C-9DA717F1FC76 Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1360203101 15020 80.91.229.3 (7 Feb 2013 02:11:41 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 7 Feb 2013 02:11:41 +0000 (UTC) Cc: "std-proposals@isocpp.org" , Sean Parent To: =?utf-8?Q?Andrzej_Krzemie=C5=84ski?= Original-X-From: std-proposals+bncBCQZJ4VEWEPRBXE2ZSEAKGQE3XHYRSQ@isocpp.org Thu Feb 07 03:12:01 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f198.google.com ([209.85.214.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1U3Gy0-0003rt-O0 for gclcip-std-proposals@m.gmane.org; Thu, 07 Feb 2013 03:12:01 +0100 Original-Received: by mail-ob0-f198.google.com with SMTP id dn14sf9783577obc.9 for ; Wed, 06 Feb 2013 18:11:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-received:x-beenthere:x-received:x-received:received-spf :x-received:references:mime-version:in-reply-to:message-id:cc :x-mailer:from:subject:date:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-google-group-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type :content-transfer-encoding; bh=4Y6cdSgtnIrUzKUZBitZc21C5ngIHdZyHdDY5lIBrT8=; b=XtNTvygzJg7g7Vs8UeiP1h8JuH94IyCbZxfJAcQm4da4QPn/NE9ucwEwF9u8Vrf4p+ 6n2EKb9qNKGZtnvgX6FxGC5qJkZdz3hAimF/eRvhIZ8Ak3IqeSf9sD4TYsIYKudvx+7O wVDiitVS4el2RHmhROH9bbc1RiwvnczEV6AP6WzlkTfhN4XLtt5hu+KRXRZJ5d9zBV6M Hbm2ELqPFJub/KSJYHGEDLBn6VTISfr6EZKMbdz9g989NXBO/zlEy52TRBd6Gwu0KZGj 6 X-Received: by 10.42.159.65 with SMTP id k1mr23311650icx.10.1360203101085; Wed, 06 Feb 2013 18:11:41 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.5.175 with SMTP id t15ls2963447igt.33.canary; Wed, 06 Feb 2013 18:11:39 -0800 (PST) X-Received: by 10.50.33.233 with SMTP id u9mr10893467igi.39.1360203099626; Wed, 06 Feb 2013 18:11:39 -0800 (PST) X-Received: by 10.50.33.233 with SMTP id u9mr10893464igi.39.1360203099585; Wed, 06 Feb 2013 18:11:39 -0800 (PST) Original-Received: from mail-ia0-x234.google.com (mail-ia0-x234.google.com [2607:f8b0:4001:c02::234]) by mx.google.com with ESMTPS id j15si5093615iga.42.2013.02.06.18.11.39 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 06 Feb 2013 18:11:39 -0800 (PST) Received-SPF: pass (google.com: domain of sean.parent@gmail.com designates 2607:f8b0:4001:c02::234 as permitted sender) client-ip=2607:f8b0:4001:c02::234; Original-Received: by mail-ia0-f180.google.com with SMTP id f27so2388780iae.39 for ; Wed, 06 Feb 2013 18:11:39 -0800 (PST) X-Received: by 10.50.151.225 with SMTP id ut1mr10664520igb.110.1360203099256; Wed, 06 Feb 2013 18:11:39 -0800 (PST) Original-Received: from [172.16.222.117] ([66.126.158.85]) by mx.google.com with ESMTPS id ig8sm6905723igc.10.2013.02.06.18.11.37 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 06 Feb 2013 18:11:38 -0800 (PST) In-Reply-To: X-Mailer: iPad Mail (10B141) X-Original-Sender: sean.parent@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of sean.parent@gmail.com designates 2607:f8b0:4001:c02::234 as permitted sender) smtp.mail=sean.parent@gmail.com; dkim=pass header.i=@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:2759 Archived-At: --Apple-Mail-F27E2A10-94FA-48C8-910C-9DA717F1FC76 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sent from my iPad On Feb 5, 2013, at 12:02 PM, Andrzej Krzemie=C5=84ski = wrote: >=20 >> > mixed assignment is illegal. Use one of the following instead:=20 >> >=20 >> > *oi =3D j; // if you want to alter the referred-to object=20 >> > oi =3D {j}; // if you want to rebind a reference=20 >> >=20 >> >>=20 >> >=20 >> > Copy constructor and copy assignment are shallow: they only (re)bind a= =20 >> > reference. Other operations are deep: this includes comparison (mixed = or=20 >> > homogenous)=20 >> >=20 >>=20 >> Is optional a RegularType? >=20 > I am not sure how to answer the question. Different people have slightly = different expectations of a regular type. > optional has: > default ctor > destructor > copy/move constructor (shallow) > copy/move assignment (shallow) > equality comparison (deep, provided that T is comparable) Then the answer would be no. The semantics of regular types are well define= d. See http://www.stepanovpapers.com/DeSt98.pdf. Copies must be equal and d= isjoint. These semantics are not regular. I find it odd that copying would = behave differently than a T& and I'm not sure what this construct buys you = over a T*. > it is not swappable yet, but I intend to add a shallow swap Given that it is copyable and assignable how is it not swappable? > I am not not sure what semantic requirements a RegularType requires. The = value compared by operator=3D=3D is not under control of the optional objec= t: it can change "asynchronously". Also the copy/move operations are not co= mpatible with operator=3D=3D: the former are shallow, the latter is deep. > =20 --=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/?hl=3Den. --Apple-Mail-F27E2A10-94FA-48C8-910C-9DA717F1FC76 Content-Type: text/html; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable


Sent from my iPad

On Feb 5, 2013, at 12:02 PM, Andrzej Krzemie=F1ski <akrzemi1@gmail.com> wrote:


> mixed assignment is illegal. Use one of the following instead:
>
> *oi =3D j; // if you want to alter the referred-to object
> oi =3D {j}; // if you want to rebind a reference
>
>>
>
> Copy constructor and copy assignment are shallow: they only (re)bi= nd a
> reference. Other operations are deep: this includes comparison (mi= xed or
> homogenous)
>

Is optional<T&> a RegularType?

I am not sure how to answer the question. Differe= nt people have slightly different expectations of a regular type.
option= al<T&> has:
  • default ctor
  • destructor
    • copy/move constructor (shallow)
  • copy/move assignment (shallow)
  • equality comparison (deep, provided that T is comparable)
Then the answer would be no. The semantics of r= egular types are well defined. See http://www.stepanovpapers.com/DeSt98.pdf. Copies= must be equal and disjoint. These semantics are not regular. I find it odd= that copying would behave differently than a T& and I'm not sure what = this construct buys you over a T*.

  • it is not swappable yet, but I intend to add a shal= low swap
Given that it is copyab= le and assignable how is it not swappable?

I am not not sure what semantic requirements a RegularType req= uires. The value compared by operator=3D=3D is not under control of the opt= ional object: it can change "asynchronously". Also the copy/move operations= are not compatible with operator=3D=3D: the former are shallow, the latter= is deep.
 

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