220 10741 article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Core Issue: deleted templates Date: Thu, 22 May 2014 18:10:42 +0800 Lines: 53 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.2\)) Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1400753463 26568 80.91.229.3 (22 May 2014 10:11:03 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 22 May 2014 10:11:03 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBK4266NQKGQEJAPUURY@isocpp.org Thu May 22 12:10:56 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ie0-f199.google.com ([209.85.223.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1WnPxd-0006zW-Hp for gclcip-std-proposals@m.gmane.org; Thu, 22 May 2014 12:10:53 +0200 Original-Received: by mail-ie0-f199.google.com with SMTP id rl12sf15098312iec.2 for ; Thu, 22 May 2014 03:10:52 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date :message-id:references:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type:content-transfer-encoding; bh=qnEMmJ7A2WMbF8HM3loHlyjVfULimQt1vlFeQm6T1QI=; b=PwQIi7wwEMG4ad/sXOf1Ax7tp36VMxpDRIluTWlxpriCNyycpbAjQc9NUL5ToowA4m EUzIditG8daibySjg3R2N/VJQO6ns8G53pF1cZ73OBvmhki1ZwsuIosn0SDDkKLkxJmS +JlvhgKc0YHSCmYMkB+1uazrmnFGBCXo4RNTPK1D+YqNETYI3LH0v0uDrlnDRrGz6/rv lT5gIrIQoh+RTkctF44MlDTYAq2ysXYdHwHDDarvFwxBDhWU/CH4CMhWhPuDEErYUgF/ wWTI7ETZxultEVb6kTH7ob78Z4hjkgAgvT1gC2YL/tSkWHy1mQ2S1kuxsnFZNsrBO2Y8 lB3g== X-Gm-Message-State: ALoCoQkxlmzsfiEsum65wP6Z48bRb0l76kTiBbw6rYA/FbzBVMM7KXnicBoZGyo6/sOUHSdFuhR/ X-Received: by 10.182.22.133 with SMTP id d5mr25653737obf.27.1400753452650; Thu, 22 May 2014 03:10:52 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.239.131 with SMTP id vs3ls2685910igc.16.canary; Thu, 22 May 2014 03:10:51 -0700 (PDT) X-Received: by 10.42.98.1 with SMTP id q1mr1339678icn.85.1400753451713; Thu, 22 May 2014 03:10:51 -0700 (PDT) Original-Received: from mail-ie0-x22e.google.com (mail-ie0-x22e.google.com [2607:f8b0:4001:c03::22e]) by mx.google.com with ESMTPS id i1si5414308igt.24.2014.05.22.03.10.51 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 22 May 2014 03:10:51 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:4001:c03::22e as permitted sender) client-ip=2607:f8b0:4001:c03::22e; Original-Received: by mail-ie0-f174.google.com with SMTP id lx4so3195098iec.5 for ; Thu, 22 May 2014 03:10:51 -0700 (PDT) X-Received: by 10.42.93.193 with SMTP id y1mr42370674icm.12.1400753451642; Thu, 22 May 2014 03:10:51 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.132]) by mx.google.com with ESMTPSA id mk2sm12248426igb.8.2014.05.22.03.10.49 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 22 May 2014 03:10:50 -0700 (PDT) In-Reply-To: X-Mailer: Apple Mail (2.1878.2) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:4001:c03::22e as permitted sender) smtp.mail=potswa@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:10741 Archived-At: On 2014-05-22, at 5:46 PM, Douglas Boffey wrote: > Would it not be better if we could explicitly delete the general template= , thus: > =20 > template > class Foo =3D delete; This really should work. I kept writing it for some time in 2011, until fin= ally I remembered that delete is only for functions. Note, if it's a serious API issue, you can accomplish something better usin= g static_assert with a fake type-dependency: template< typename T > class Foo { static_assert( std::is_same< T, void >::value, "Invalid template argume= nt." ); }; This can be encapsulated in a pseudo-CRTP base class, although it makes the= diagnostic less user-friendly. > Likewise for template functions and template variables. It already works for function templates. Much the same thing can be accomplished by declaring a variable template wi= th a type that cannot be constructed, hence generating an error at the offe= nding instantiation. Disabling an explicit specialization of a variable tem= plate might not be as elegant, but you can probably use SFINAE in the prima= ry template instead. (Or concepts, once we get those.) In principle, though, I suppose you're right about variable templates. > Foo &operator=3D(const T &t) =3D delete; // Are we deleting the templat= e or the member function? There is no distinction. Deleted functions produce an error when selected b= y overload resolution. --=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 http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. .