220 12753 article Path: news.gmane.org!not-for-mail From: Sebastian Redl Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Placeholder literals Date: Tue, 9 Sep 2014 15:15:12 -0700 (PDT) Lines: 67 Approved: news@gmane.org Message-ID: References: <570663A9-F617-442F-9B48-5B6E7311AE72@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_1235_114525602.1410300912373" X-Trace: ger.gmane.org 1410300928 31825 80.91.229.3 (9 Sep 2014 22:15:28 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 9 Sep 2014 22:15:28 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBD47DAWPX4ARB4PXXWQAKGQEE3GTGKQ@isocpp.org Wed Sep 10 00:15:22 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oa0-f72.google.com ([209.85.219.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XRTgw-0001uV-Tp for gclcip-std-proposals@m.gmane.org; Wed, 10 Sep 2014 00:15:15 +0200 Original-Received: by mail-oa0-f72.google.com with SMTP id m1sf86999508oag.11 for ; Tue, 09 Sep 2014 15:15:14 -0700 (PDT) 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:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=Bxg2IPwln0Y9QYN7mR/ozE6KsYzsHMjg0/vsqZ7q5IM=; b=LGCXHgvCUn2ucvU9+E6LjnYlQXdDFSiWhAVWknnD1NxKRTY/qkEHiF0xwaL9Yblydk aq8Y4C1eMpPJ9Yh1FWzrkC+sMjYNSicQQJ92n6BwjG9ckiMLKd8OVkUvT5D606epRtSb LUQrN0DT4VythZWNY4HqAM2U2pi8HLg6spkPyAWuZ0OG/DHnaLSZUny2LITjy4yv3ar3 /r6EohYsDtsFWhfnTK9BxoO+bV8ZcJ3LWM6vPXZD5KeMZDcIpz3x07f/ttaEqWCSuhjt scGebGnr5hEGmT2Iefi6vm+KGQRMDOwN0InPRXQ31liBhHgtSRA4gbVZ86TMTS2M42dY OE+A== X-Gm-Message-State: ALoCoQnEhuEkmqtCXJ/8QBjAB036gv6SDsMyMHd3m7WVvv3Xz6pqojTJM5mtEn/hwSaBMzuTQWhN X-Received: by 10.50.112.68 with SMTP id io4mr18484810igb.0.1410300914020; Tue, 09 Sep 2014 15:15:14 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.31.180 with SMTP id f49ls1027557qgf.39.gmail; Tue, 09 Sep 2014 15:15:13 -0700 (PDT) X-Received: by 10.140.37.39 with SMTP id q36mr74545qgq.10.1410300913122; Tue, 09 Sep 2014 15:15:13 -0700 (PDT) In-Reply-To: <570663A9-F617-442F-9B48-5B6E7311AE72@gmail.com> X-Original-Sender: wasti.redl@gmx.net 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:12753 Archived-At: ------=_Part_1235_114525602.1410300912373 Content-Type: text/plain; charset=UTF-8 On Sunday, August 24, 2014 3:23:00 AM UTC+2, David Krauss wrote: > > Why not add literal operator templates returning placeholders? > > Compare: > std::placeholders::_1 // old > 1param // new > > It's not actually possible to implement that. The placeholders need to encode their index in the type (std::is_placeholder<_1> must derive from std::integral_constant), and it's not possible to write a function, even a constexpr function, that returns different types for different arguments, as the operator ""param would have to do in this case. Sebastian -- --- 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/. ------=_Part_1235_114525602.1410300912373 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Sunday, August 24, 2014 3:23:00 AM UTC+2, David= Krauss wrote:
Why not add literal operator templates returning placeh= olders?

Compare:
std::placeholders::_1 // old
=
1param = // new


It's not actually possib= le to implement that. The placeholders need to encode their index in the ty= pe (std::is_placeholder<_1> must derive from std::integral_constant&l= t;int, 1>), and it's not possible to write a function, even a constexpr = function, that returns different types for different arguments, as the oper= ator ""param would have to do in this case.

Sebastian

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