220 27720 article Path: news.gmane.org!.POSTED!not-for-mail From: Cleiton Santoia Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: if constexpr in class declaration Date: Tue, 9 Aug 2016 10:30:47 -0700 (PDT) Lines: 119 Approved: news@gmane.org Message-ID: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_365_1335599945.1470763847662" X-Trace: blaine.gmane.org 1470763855 24987 195.159.176.226 (9 Aug 2016 17:30:55 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 9 Aug 2016 17:30:55 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCBMVWMTUUNBBSFGVC6QKGQEBUTDY5Q@isocpp.org Tue Aug 09 19:30:51 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pa0-f71.google.com ([209.85.220.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bXArZ-0006LP-MS for gclcip-std-proposals@m.gmane.org; Tue, 09 Aug 2016 19:30:50 +0200 Original-Received: by mail-pa0-f71.google.com with SMTP id pp5sf32861133pac.3 for ; Tue, 09 Aug 2016 10:30:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=EDj4V8vgCMKUBkaidiYnmeeGmC3XiT7nrGh9kCuox4Q=; b=KGXinBgjRNErh1hsRkEiQ8ZjJrfL6z0qBhxcoYEdoGb7ndgWOorhg571foKWLqvpqt xWW20DKB2EJqEIwiVq1DMKCpKb76gthovIBJ6dWDvG2rTD3rZ71E8CEqKcyHV/oX4+Mw 9TvD51M9uHuntV+3poOVFRaxSjCU2Y1GshlMOYwkZc418No1h+vDgo1WgEM1GYAu0hVm uWhhCFlNDvd19gkdT/H970XBW9AFehp7Nl83K3PzfZ8sb38pRjp0v+Y+uy/5z2+moHGS Ds158zy2SiDdl856q5ZlshqFaR+NhBX/c154UjcjvfcJ5lBwYys1m9DwDvj8r6o1Zpl2 6Asg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=EDj4V8vgCMKUBkaidiYnmeeGmC3XiT7nrGh9kCuox4Q=; b=kM6hri7ms3IXTV65V1oEkEd1z4Gq/yC2MogKUB80i04OCz9LojrAosXK7VGnD0GRZY xncUTfDQHtGPLG5yevt2aBiQwXlxaBPPo85szdek115Mf3WeTREH6A+dTgyDObT3us2c ptTYF7z7u881XU2Kp6NkJYee16G0HLvklHIcGqsY2ZiYP76WBN0XpKwNDjKdyhcelouL 8m2o7ao1irWMA7x4utP1P+Uy+9pG6InQsGpi3P/Lry7aKvc51NwMlsm4n4z71WfJHL/m 7W5AGFy61yD20OHarvBacXyA1Gb3KNSqUWC08ilcdbYNqrstrAhraWEOsmrx0zOpaFy/ FpDg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=EDj4V8vgCMKUBkaidiYnmeeGmC3XiT7nrGh9kCuox4Q=; b=LenC0TdC/OTWoD/ZQYNUAJJRvPsNa91aZO3nnsOe8dnLHLlLg+7LPw/dvw0wzKGNN2 AgYxIQq5eHfH67y59uycFS0gW3CcFvfdSLlF4GOAsOQGl/5lYZj/wTo4a35lEjVe5s6r KbCX3FLDtlFw7i1cxMgo8WCnoV151+UMF2sXvUjJF+D6PBBg7kRo7EaZmU/Ih3IyQzkC ZfxcGe5H7trmx7nft7HdPVNa9WF9COpz0KOzqcnxO5GW4L05r3GSY0TVRlnJyfplAgsE Abh19cMOo3bpxmz1ApfwUfEnBnVSiq4pV7rhjlfBrwE9lODayRLVsz+Sqq4RRjWx4AOl o9EQ== X-Gm-Message-State: AEkoousJFft1cYTjPplJgzWOobaTpA447dcYbSjumpELpYC0I5+oBvedMF1mP7+BnFfF3g== X-Received: by 10.98.78.203 with SMTP id c194mr84128338pfb.3.1470763849565; Tue, 09 Aug 2016 10:30:49 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.82.81 with SMTP id d78ls5794773itb.17.gmail; Tue, 09 Aug 2016 10:30:48 -0700 (PDT) X-Received: by 10.36.230.194 with SMTP id e185mr808562ith.9.1470763848317; Tue, 09 Aug 2016 10:30:48 -0700 (PDT) X-Original-Sender: cleitonsantoia@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:27720 Archived-At: ------=_Part_365_1335599945.1470763847662 Content-Type: multipart/alternative; boundary="----=_Part_366_873861596.1470763847663" ------=_Part_366_873861596.1470763847663 Content-Type: text/plain; charset=UTF-8 "If constexpr" is defined only as statement, someone thought about allow it into class definitions like this : template struct X { if constexpr (std::is_arithmetic_v) { double value; } else constexpr { std::string value; } }; X::value // value is double X::value // value is string I know that this particular example will be better with concepts, but the question remains... -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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"If constexpr" is defined only as statement= , someone thought about allow it into class definitions like this :

template <class T>
struct X {
=C2=A0 = =C2=A0if constexpr (std::is_arithmetic_v<T>) {
=C2=A0 =C2=A0 =C2=A0double value;
=C2=A0 =C2=A0} else constexpr {
=C2=A0 =C2=A0 =C2=A0std::string value;
=C2=A0 =C2=A0}
};

X<int>::value =C2=A0 =C2=A0 // value is double
X<Myclass>::value /= / value is string

I know that this particular = example will be better with concepts, but the question remains...=C2=A0


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