220 39123 article Path: news.gmane.org!.POSTED!not-for-mail From: Zhihao Yuan Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: RE: Concept-defined placeholder type Date: Thu, 12 Jul 2018 16:20:18 -0400 Lines: 49 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" X-Trace: blaine.gmane.org 1531426697 14743 195.159.176.226 (12 Jul 2018 20:18:17 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 12 Jul 2018 20:18:17 +0000 (UTC) To: mihailnajdenov@gmail.com, 'ISO C++ Standard - Future Proposals' Original-X-From: std-proposals+bncBCSKRWMD4EHBBB7QT3NAKGQEVYMJQQQ@isocpp.org Thu Jul 12 22:18:13 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wr1-f71.google.com ([209.85.221.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fdi2X-0003l5-3U for gclcip-std-proposals@m.gmane.org; Thu, 12 Jul 2018 22:18:13 +0200 Original-Received: by mail-wr1-f71.google.com with SMTP id z13-v6sf4759967wrq.3 for ; Thu, 12 Jul 2018 13:20:24 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1531426824; cv=pass; d=google.com; s=arc-20160816; b=uTZRwWgpKknism22N3gmXR5COEGcUHIwJimmUGfDo0hG/KpSlZlu/d0vLI1+EBgbaW IypmnlAiz9ZM1WuTrrycBmKHGwJ6Ql7NOhTaigfQXJq8ep5qSpC59xk7yDs/wH8Iu+6E AXl1uRwR73mOj48ZjTP6phHk0xrzT0K/2M0CeUojWiRw4cDcshfLenAw9kCN6PDQpgEO rHytR8n0IBtMhUqskEiSRFFh+k8s9QC5E3pryTsJpg/JZHFjOjufMUt554DAp+vKj6jI 3tNVeJi7m2w0lipCBqClVLyRDYnnu8WD3HXwrt8aXzrFKEZNgU/i/MduSoYbBCs81xbC DH6w== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:mime-version:feedback-id:references :in-reply-to:message-id:subject:reply-to:from:to:date :arc-authentication-results:arc-message-signature:dkim-signature :arc-authentication-results; bh=V0QXf4ybJFIKscyAPt99TCUbhEuUSQhVAobVAIwMjV4=; b=NMjPyy3HSqllmb+4jfbdKQAMFBOQtHDZjQJ0lozPjhw7OTxGd/ToQmZKCKZMWY8QK5 7jjfRf5FC4SfPYGglo1M8NX0el/Swqo2kHcqGhSjuYIhnYxMeNFtDI+qfOFXvzsOJbw9 vP+3cexHGkO2EJ1UaZV4awkc+Rm4HTADtFFFBGbWMRsxpoVNNQchLo9aO61Ug/ChhP9m bctE7UJTOho7yLTcGjyhdF8PaR36nHNaFbIdTL0s39hioncnfroZJQjKh2TP41bSbIRy 5qh+R+UyfHTN0jwsNxxxIfK/+2FGycyYezkQFFAFWjh/eoeQVGNEWxWlcTDJwuU2aqNx SfOA== ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@miator.net header.s=protonmail header.b=DpGzUx8n; spf=pass (google.com: domain of zy@miator.net designates 185.70.40.132 as permitted sender) smtp.mailfrom=zy@miator.net DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:to:from:reply-to:subject:message-id:in-reply-to:references :feedback-id:mime-version:x-original-sender :x-original-authentication-results:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=V0QXf4ybJFIKscyAPt99TCUbhEuUSQhVAobVAIwMjV4=; b=diLvUUP1aQnnk6uXT42nD2krEQGrz7aWAL1V4sU10R+sadRVus18AvMU6eT8Vz8p7S 4ha6WbZQWmKYFd5oRZNthhARBh/gfCnee8nqyFAFhcYTtISqDJYkwfLOJcZm/oZnXAA5 Vixyg7zPjkZpQotDeAEkjKKtMNyazPHXAGIVUlkZAXBW7yVNMr+6hEzwVqM9ny/p9SHH F8OJwtQ0myFQaIfjplqju2ASl/HbEkRRHkaU0ecxTUSLaIxlT3Exf8SiGxJ04lnecxfC 8ZoPuOQ0b0ChAxj3/Wb9mL/CXkxnI6Rxcrh9+AtGFVl38C62G/O9ouXVjSnyxPrgeSzK E7mA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:to:from:reply-to:subject:message-id :in-reply-to:references:feedback-id:mime-version:x-original-sender :x-original-authentication-results:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=V0QXf4ybJFIKscyAPt99TCUbhEuUSQhVAobVAIwMjV4=; b=PrizXVL9zr41BzlRAG1w7urhttGsuOJURK5MXHJfCVPUUL6cUvlefh9GCC0vXKLcAi esnYHqKKPkv5q7v6FnhVUhWLYxCeREayJdSR6eXKfTJ+0/2PTfJYcIEqbCVhul0BUUZ/ CAfzpP5P74yT8MDtP2v2MnP6X7UvUWHIS83j4iDOlhVE5jDvSQPUoU1q1NvDd4FiyEJC LHMpHNts/EQEh+I0zK2iO7bhnH8SS1qJJYykXbRbzePfP6zIIhEe22lGgNjV9ph92yBn b8gqonP+cs7PLed2u2u3zrNcd0iH9vRvQ0Z7Eqv9Isj8mLswd9QflwWK9oXFXzFtLUx4 gVjA== X-Gm-Message-State: AOUpUlErdzvQ2pmvGr8N2Mfj0hsTYSYloPXAHJe+mWLsm+tWdrVCE0Xy 5qNmqoNMFhw8cUiib6BXxrvQJQ== X-Google-Smtp-Source: AAOMgpdJ7nvINwEdnQXtDFYV1GZZuRTszbiuhC4ylvd61OkYSMVqjZnEBEyKcl/tNRHGRSz4pURQBg== X-Received: by 2002:a1c:f405:: with SMTP id z5-v6mr356233wma.1.1531426824375; Thu, 12 Jul 2018 13:20:24 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a1c:7a15:: with SMTP id v21-v6ls1361225wmc.10.canary-gmail; Thu, 12 Jul 2018 13:20:23 -0700 (PDT) X-Received: by 2002:a1c:30d2:: with SMTP id w201-v6mr2106074wmw.47.1531426823165; Thu, 12 Jul 2018 13:20:23 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1531426823; cv=none; d=google.com; s=arc-20160816; b=eJsKiakN5cCnX0T2IyWztPXgsaSy0CTqFMhygfW8txcjhH9enwfmmzkxEiV3N1nC3X KDGXHjGceVU9wgubTu9wtL/nBidV5gge/TqkYQTY4tPDZf1aM06RmqRoEtohFUPy8sbn NuRna3T10A0eGupUJsvA15WnI/kZV0HLOm6Wt1btFHvXyTVukYqRakuiSmZYXDFHpG3R 8wMGPglyHrtBTD4g6ErfiwLgnIxmixy3nqEBIpGqnrez01Cx3QHjI7fsxP7KOXMrVIQg 12G9+Z2S8HpkADZ1JSxMAeAUT31xHgeZnw2WAbURSkcL5U+XnTZZ1dI/YsuRpeHaOsWE tykA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:mime-version:feedback-id:references :in-reply-to:message-id:subject:reply-to:from:to:dkim-signature:date :arc-authentication-results; bh=fNoCp0itWVeUJ+PmA21ZYLtRyjuAj7flWb1wOvPm3bo=; b=a5AVsTWIayIkhylorpnoWt6QHOQEPWoMt0gRYaeAZuqExvP6JgI++QOUIiwFV5zBSQ ZEj8oxBo68yfWVvLy7V5o0UNs/GMoz0iAJ7RmfIZWd5Aqe5J3yyeOHYgaQCPQitC0NGr JUkiItvdCmpAAXQhs5Urhez0Es4PqsKBcC3oqZtFotpPVEA5qqy49f+vHL4XUCyLfIOm Mgc1SafAPZeAxHcFTRpIO2jdEbXtmwGtul1POeHJ3QUVuRcwuYUkvR58mU5SNOnbfHuO IPpwBJn0nJEEvwsuLjKnjHOoDUO3n8H2Lb0G8ke7yxibcU+nhg3gBPrblim4feHS/fcB 0Rsw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@miator.net header.s=protonmail header.b=DpGzUx8n; spf=pass (google.com: domain of zy@miator.net designates 185.70.40.132 as permitted sender) smtp.mailfrom=zy@miator.net Original-Received: from mail-1857040132.protonmail.ch (mail-1857040132.protonmail.ch. [185.70.40.132]) by mx.google.com with ESMTPS id w11-v6si20150732wrn.206.2018.07.12.13.20.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 12 Jul 2018 13:20:23 -0700 (PDT) Received-SPF: pass (google.com: domain of zy@miator.net designates 185.70.40.132 as permitted sender) client-ip=185.70.40.132; In-Reply-To: Feedback-ID: xu1i2ADzKwGyrUl8KbXpsa1PQSI0Bc21qlX1V7gpMylRDQPR42YBpWcLHW4brubvCmGM18xDo5tgsD-vWFu_cQ==:Ext:ProtonMail X-Original-Sender: zy@miator.net X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@miator.net header.s=protonmail header.b=DpGzUx8n; spf=pass (google.com: domain of zy@miator.net designates 185.70.40.132 as permitted sender) smtp.mailfrom=zy@miator.net 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:39123 Archived-At: From: mihailnajdenov@gmail.com Sent: Thursday, July 12, 2018 4:58 AM > With types > > template<. . .> > auto func() > { > Concept Type; > > if constexpr(something) > Type var = . . .; > else > Type var = . . .; > > // use Type; > } > > But this works even if Concept Type is introduced in scope (other means included)! > if constexpr - will physically remove the scopes altogether. And if it is not a constexpr if, then we could init it outside of scope by other means It doesn't, "var" cannot be looked up at the "// use Type" location, so you cannot even use decltype(var) there. > namespace n { > > StandardLayoutType T; //< allowed? > > template > void uploadToGPU(Producer& producer) > { > T item = producer.next(); > } That's the kind of bug that I'm looking for... It shouldn't be allowed. -- Zhihao Yuan, ID lichray The best way to predict the future is to invent it. _______________________________________________ -- 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/lncm-v8bR9K6sqXzAewvVZNg2wuf0txaLwMD-TpIqbIGq7zL25pGi5DsziWZ92BFQ1HfQftRe9FGbSENOBMkWrzjPjrR2uKsayJJRFA4AQI%3D%40miator.net. .