220 16064 article Path: news.gmane.org!not-for-mail From: mobi phil Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: const T* operator->() const Date: Fri, 6 Feb 2015 10:50:43 +0100 Lines: 94 Approved: news@gmane.org Message-ID: References: <56a7727d-9839-45c9-be72-a6ecb61f38c9@isocpp.org> <2900481.dbBOWPyqhq@tjmaciei-mobl4> <1932997.CYfMEhPeyI@tjmaciei-mobl4> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a113f8f8aa001f4050e685ae0 X-Trace: ger.gmane.org 1423216255 18128 80.91.229.3 (6 Feb 2015 09:50:55 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 6 Feb 2015 09:50:55 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDF3H34L74HRB4442KTAKGQEW2SVXNQ@isocpp.org Fri Feb 06 10:50:45 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f71.google.com ([209.85.218.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YJfYj-0003PC-Mx for gclcip-std-proposals@m.gmane.org; Fri, 06 Feb 2015 10:50:45 +0100 Original-Received: by mail-oi0-f71.google.com with SMTP id x69sf2438768oia.2 for ; Fri, 06 Feb 2015 01:50:44 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=iiyh27xdQANXbg2ntjL4Bfd+wF4DQmT9zYJB6FK7PwA=; b=dZ+d0NLL/nJlOQOqRRlQHdQ0W6PyBOJpXLvAPswX5IHBvLvBH2SIE+ZnT9XQtlB0iE LH9kY7e+wITkiwbfxxfrCxtF6LTmJp+qUfPl/Bbi8MTXd5ISULU6FeRtHY6RBEoFn6Pn 8ysmaAfD/ihgR/1GVMrRtf8zT3aCwZZ3ejZDepvcfxODtAlvip5vDTnZDuNvPMsVYA2k F0aw2z5sNIv5f/rHRDU4rNkazECKRHaaGLLfxQdlZPNgnOyvP+mfbuIQwPR/ISfL4cGj DHsrVvlk/HakkX0Y27LDECG4JVIMnfAwaDFuJl4kgSsJZbHIgKHTMGbmF/xd3+i8W/eQ KriA== X-Gm-Message-State: ALoCoQn8DYZ9V5kTvZOy0HJJgdTv1N7c/KyFw7JWHttvquohWjkK1jpdb3Un/RFt0s8wUe1U4WiU X-Received: by 10.42.40.147 with SMTP id l19mr10916776ice.34.1423216244462; Fri, 06 Feb 2015 01:50:44 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.25.132 with SMTP id 126ls796154ioz.31.gmail; Fri, 06 Feb 2015 01:50:43 -0800 (PST) X-Received: by 10.107.3.159 with SMTP id e31mr9902527ioi.65.1423216243755; Fri, 06 Feb 2015 01:50:43 -0800 (PST) Original-Received: from mail-ie0-f172.google.com (mail-ie0-f172.google.com. [209.85.223.172]) by mx.google.com with ESMTPS id v9si275750igd.54.2015.02.06.01.50.43 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 06 Feb 2015 01:50:43 -0800 (PST) Received-SPF: none (google.com: mobi@mobiphil.com does not designate permitted sender hosts) client-ip=209.85.223.172; Original-Received: by iery20 with SMTP id y20so55212ier.1 for ; Fri, 06 Feb 2015 01:50:43 -0800 (PST) X-Received: by 10.107.8.67 with SMTP id 64mr9852942ioi.67.1423216243365; Fri, 06 Feb 2015 01:50:43 -0800 (PST) Original-Received: by 10.50.186.167 with HTTP; Fri, 6 Feb 2015 01:50:43 -0800 (PST) In-Reply-To: <1932997.CYfMEhPeyI@tjmaciei-mobl4> X-Original-Sender: mobi@mobiphil.com X-Original-Authentication-Results: mx.google.com; spf=none (google.com: mobi@mobiphil.com does not designate permitted sender hosts) smtp.mail=mobi@mobiphil.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:16064 Archived-At: --001a113f8f8aa001f4050e685ae0 Content-Type: text/plain; charset=UTF-8 On Fri, Feb 6, 2015 at 2:04 AM, Thiago Macieira wrote: > On Friday 06 February 2015 01:06:54 mobi phil wrote: > > > QSharedDataPointer does COW using operator->. > > > > > > However, it copies when you call the non-const operator->, even if your > > > use is > > > read-only. > > > > then you may agree that there would be some added value in such a > > construct... Does not make sense to copy if the method is read-only, > isn't > > it? > > That doesn't work if I'm accessing a member. > > For example, the expression > type->member > > Is an lvalue and could be assigned to. But that doesn't mean that it is > assigned to, so the operator-> would have no choice but to copy and assume > that you do. > well, if you are directly accessing members, you would compromise the implementation of COW, wouldn't you? -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. --001a113f8f8aa001f4050e685ae0 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Fri, Feb 6, 2015 at 2:04 AM, Thiago Macieira <<= a href=3D"mailto:thiago@macieira.org" target=3D"_blank">thiago@macieira.org= > wrote:
On Friday 06 February 2015 01:06:54 mobi phil wrote:<= br> > > QSharedDataPointer does COW using operator->.
> >
> > However, it copies when you call the non-const operator->, eve= n if your
> > use is
> > read-only.
>
> then you may agree that there would be some added value in such a
> construct... Does not make sense to copy if the method is read-only, i= sn't
> it?

That doesn't work if I'm accessing a member.

For example, the expression
=C2=A0 =C2=A0 =C2=A0 =C2=A0 type->member

Is an lvalue and could be assigned to. But that doesn't mean that it is=
assigned to, so the operator-> would have no choice but to copy and assu= me
that you do.

well, if you are directly accessing member= s, you would compromise the implementation of COW, wouldn't you?
<= /div>

--

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