220 2760 <3aca8f41-7a21-40d8-9bf9-9c27dfa778f3@isocpp.org> article Path: news.gmane.org!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: optional references -- take 2 Date: Wed, 6 Feb 2013 18:40:11 -0800 (PST) Lines: 131 Approved: news@gmane.org Message-ID: <3aca8f41-7a21-40d8-9bf9-9c27dfa778f3@isocpp.org> References: <8d57e9e9-e4cc-441c-abeb-e6526531fad5@isocpp.org> <3534ECE0-D67E-443E-9593-76B644FDDF6A@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_1130_27364047.1360204811794" X-Trace: ger.gmane.org 1360204815 27516 80.91.229.3 (7 Feb 2013 02:40:15 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 7 Feb 2013 02:40:15 +0000 (UTC) Cc: =?UTF-8?Q?Andrzej_Krzemie=C5=84ski?= , Sean Parent , sean.parent@gmail.com To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCEKFTV6ZUMBBDNIZSEAKGQERX4TXMI@isocpp.org Thu Feb 07 03:40:34 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vb0-f69.google.com ([209.85.212.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1U3HPc-0007zL-O9 for gclcip-std-proposals@m.gmane.org; Thu, 07 Feb 2013 03:40:33 +0100 Original-Received: by mail-vb0-f69.google.com with SMTP id ff20sf2677750vbb.0 for ; Wed, 06 Feb 2013 18:40:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-received:x-beenthere:x-received:date:from:to:cc:message-id :in-reply-to:references:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-google-group-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=EFMjMPtWRwdbvRlWu44F36s5MvV04E1AnK5xKrA6Hxs=; b=g/CD/XrXOQTLgKppiEuvEIJnzlMfP2RZYZxgxlUN6EI4C73YpqZ5yb9JCje4KeqDaj /vreDcs7afbcr+MqoS6suSk5mOrn1dFeWCsmx0dzKdrZYFjMuLFYOjzlNkCdrc5f/k/X B8vbLN2zHpF9ZVH8+G4+/UAmX3wZmOZcZsCVgOTbeBjx+mWGC6twHRNofccQ/7EGq4lV Q2F/CBUocTKvjjqvR04vQ5JWs+cb8OUwnDMx3X3sSeDMjOCMvyQZSusxyYOzGZJzi1+D qQJVOTohtJf7djOn/CcO3Fd5R+m61NyaOfwFyOngHJBzCATUo/uInUpxfxlxQ3l5qxcG V0Uw== X-Received: by 10.236.134.43 with SMTP id r31mr13832991yhi.6.1360204813529; Wed, 06 Feb 2013 18:40:13 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.37.134 with SMTP id y6ls565161qej.96.gmail; Wed, 06 Feb 2013 18:40:12 -0800 (PST) X-Received: by 10.49.35.77 with SMTP id f13mr2694717qej.4.1360204812357; Wed, 06 Feb 2013 18:40:12 -0800 (PST) In-Reply-To: <3534ECE0-D67E-443E-9593-76B644FDDF6A@gmail.com> X-Original-Sender: jmckesson@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:2760 Archived-At: ------=_Part_1130_27364047.1360204811794 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Wednesday, February 6, 2013 6:11:37 PM UTC-8, Sean Parent wrote: > > > > Sent from my iPad > > On Feb 5, 2013, at 12:02 PM, Andrzej Krzemie=C5=84ski >=20 > wrote: > > > > 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= =20 >> or=20 >> > homogenous)=20 >> >=20 >> >> Is optional a RegularType?=20 >> > > I am not sure how to answer the question. Different people have slightly= =20 > 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=20 > defined. See http://www.stepanovpapers.com/DeSt98.pdf. Copies must be=20 > equal and disjoint. These semantics are not regular. I find it odd that= =20 > copying would behave differently than a T& and I'm not sure what this=20 > construct buys you over a T*. > That's really the question I have about this whole `optional` thing:=20 what exactly is the use case for this functionality that `T*` can't also=20 cover? --=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. ------=_Part_1130_27364047.1360204811794 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

On Wednesday, February 6, 2013 6:11:37 PM UTC-8, Sean Parent wrote:=

Sent from my iPad

On Feb 5, 2013, at 12:02 PM, Andrzej Krzem= ie=C5=84ski <akrz...@gmail.com> wrote:


> mi= xed 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/DeSt= 98.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*.

That's really the question I have about this whole `optiona= l<T&>` thing: what exactly is the use case for this functionality= that `T*` can't also cover?

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