220 24303 <4718878.Khnkm2gQof@tjmaciei-mobl4> article Path: news.gmane.org!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Choosing value categories using a specialized traits class Date: Wed, 10 Feb 2016 10:51:51 -0800 Lines: 47 Approved: news@gmane.org Message-ID: <4718878.Khnkm2gQof@tjmaciei-mobl4> References: <20160210161034.4898896.57740.4502@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1455130324 13252 80.91.229.3 (10 Feb 2016 18:52:04 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 10 Feb 2016 18:52:04 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBSUN522QKGQERVKXYSA@isocpp.org Wed Feb 10 19:51:55 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f198.google.com ([209.85.217.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aTZrn-0005p3-Jk for gclcip-std-proposals@m.gmane.org; Wed, 10 Feb 2016 19:51:55 +0100 Original-Received: by mail-lb0-f198.google.com with SMTP id jx7sf9242455lbc.2 for ; Wed, 10 Feb 2016 10:51:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=from:to:subject:date:message-id:user-agent:in-reply-to:references :mime-version:content-transfer-encoding:content-type :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=zC9qW6IbB20wBd60tYcj428WCKJzsHhSq4nCMiGxZuo=; b=nNbfiuIam6V5k19cHfBUJ/bYwJQCkERdaFdwtB0wJ6Miceo3VrLzg07uHtNeoX5mRQ rCEjFobe8jtpZkOqO/uQjweeli5CpOrD993GG4yZXcGUCb5wcQ2u5RKpMW/DgYD0L1VY uMCS1j4NK4QIONNGYfp7wM8mx0tgDR7K3e/B5UmtEryVFXZGncM2eer1ar4quhAfIIGH Z6mD4K02Gb03p434vtp41ov2vzrRcrBB18zNLSnZKfZ15B+bPqNxINI5NlMMYcgn85W1 WHaXeyeNFoLNpYmsD5bIOCp4G+EvldYFbidVc61nadvNg42GnjscAREhHgnsB X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:subject:date:message-id:user-agent :in-reply-to:references:mime-version:content-transfer-encoding :content-type:x-original-sender:x-original-authentication-results :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=zC9qW6IbB20wBd60tYcj428WCKJzsHhSq4nCMiGxZuo=; b=Xls4a6cFrsm1ajgtDurSG7RJsf24hHK8UZdhojp4vO8z5e+zBki72JN9YiYtNaJq+Q me2gWGn0l8lIHvdy2gMz1/xtpjHQXABeFlzltcZXwO72wnMZrSWNE28F85Fbokj00Wx9 LO0ElXMzw/eEXinF4YPaLvwaZJLb68aqO5gcaoxIMv+SNhCW9/4G+A1YmvVcLqZgkDGa 2Nu142YGh3tb8dcdcPNtcKw1MMwzWspMiJpOvhZe1jxytgEmDII/DEGQWjrUTNw/AVvH 2Di1QGHRNOmxQmTWfk/k5cY/JhL+MyECqDGaNScyq3ewrFirzDvOanL3s X-Gm-Message-State: AG10YOQB5QCR9iMV3amP6V7tZDsMUq47XyGt8k6mZILjfkr7RjlkzBFQ935GtvJ8laqljg== X-Received: by 10.194.171.198 with SMTP id aw6mr5041737wjc.1.1455130315160; Wed, 10 Feb 2016 10:51:55 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.47.195 with SMTP id v186ls236775wmv.21.gmail; Wed, 10 Feb 2016 10:51:54 -0800 (PST) X-Received: by 10.194.175.198 with SMTP id cc6mr41761078wjc.24.1455130314027; Wed, 10 Feb 2016 10:51:54 -0800 (PST) Original-Received: from gondolin.macieira.info (gondolin.macieira.info. [78.47.120.188]) by mx.google.com with ESMTP id y142si32197080wmd.54.2016.02.10.10.51.53 for ; Wed, 10 Feb 2016 10:51:54 -0800 (PST) Received-SPF: pass (google.com: domain of thiago@macieira.org designates 78.47.120.188 as permitted sender) client-ip=78.47.120.188; Original-Received: from tjmaciei-mobl4.localnet (unknown [134.134.139.76]) by gondolin.macieira.info (Postfix) with ESMTPSA id 7DAB611AC3C for ; Wed, 10 Feb 2016 10:51:53 -0800 (PST) User-Agent: KMail/5.1.1 (Linux/4.4.0-3-default; KDE/5.18.0; x86_64; ; ) In-Reply-To: <20160210161034.4898896.57740.4502@gmail.com> X-Original-Sender: thiago@macieira.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of thiago@macieira.org designates 78.47.120.188 as permitted sender) smtp.mailfrom=thiago@macieira.org Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:24303 Archived-At: On quarta-feira, 10 de fevereiro de 2016 11:10:34 PST Tony V E wrote: > Not a bad idea.=20 >=20 > But I'd rather see some kind of language feature for param passing. A "pa= ss > by copy if cheap"=E2=80=8E syntax. Also a pass by copy-if-write (for case= s where > the function body I available to determine that).=20 >=20 > Vaguely speaking. Agreed. For my Qt6 QVector, I have: typedef typename std::conditional::value ||=20 std::is_pointer::value, T, const T &>::type parameter_type; Which is "good enough", but could be better. It won't catch trivial types t= hat=20 can be passed in registers, such as structs with size less than a register = (or=20 two). Maybe we want a type trait (name TBD) that is true for those types. The=20 standard should say that it is true at least for fundamental types and=20 pointers, the rest to be implementation-defined. This also goes back to the discussion on relocatable types and the destruct= ive=20 move. --=20 Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Software Architect - Intel Open Source Technology Center --=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 https://groups.google.com/a/isocpp.org/group/std-propos= als/. .