220 16679 article Path: news.gmane.org!not-for-mail From: Gabriel Dos Reis Newsgroups: gmane.comp.lang.c++.isocpp.proposals,gmane.comp.lang.c++.isocpp.general Subject: Re: An implementation of enhanced auto deduction and abbreviated template syntax using Clang Date: Wed, 4 Mar 2015 03:45:01 +0000 Lines: 97 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: ger.gmane.org 1425440719 21433 80.91.229.3 (4 Mar 2015 03:45:19 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 4 Mar 2015 03:45:19 +0000 (UTC) Cc: "std-discussion@isocpp.org" , "c++std-core@accu.org" To: "" Original-X-From: std-proposals+bncBC76L47644CRBQH73GTQKGQER3OC53Y@isocpp.org Wed Mar 04 04:45:06 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f198.google.com ([209.85.214.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YT0F8-0002Nq-GV for gclcip-std-proposals@m.gmane.org; Wed, 04 Mar 2015 04:45:06 +0100 Original-Received: by obcuz6 with SMTP id uz6sf22403186obc.1 for ; Tue, 03 Mar 2015 19:45:05 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:thread-topic:thread-index :date:message-id:references:in-reply-to:accept-language :content-language:content-type:mime-version:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=KjwdTCp7Q2BFLK1lvcr8mA/FZDVqrh6ZDTAmOKmhmgk=; b=EUclp2wIGus0KB8AcheSpvQfLO8mAr7Wl2mlsktdtocaGMMnwaaHxVPGW3HbE7nWan 5dA3VgET9KpVCYJlWrDzIORSsnLHTBTPUzO1cFp2yba4+AA89XIzkybaqDgn2vzu1Nxf ZXEDRNAk7VESKOMu6sMeycYeB5zin4izbzEqE0OX7zLUP4018IJ+hqM848Z1HbKcco2z lrD0elDBjw5+2b+NSjadj7YgaMqnZGC9UjyWkKkdYvdrI7Fv/8xzW0CbPIozD9300aJy Yv3PXRzHbMWV3fKwfSsPq0NPUjf+c9jzQuyRrV9K2OZP6t X-Gm-Message-State: ALoCoQled58TjY6RyH1XEsovLde4F7BQ4UIhvpXYahvICLqvaxxuQrcCtfQsRjOGnBYpQarekPEu X-Received: by 10.183.10.164 with SMTP id eb4mr2531204obd.48.1425440705366; Tue, 03 Mar 2015 19:45:05 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.163.208 with SMTP id m199ls448756ioe.59.gmail; Tue, 03 Mar 2015 19:45:04 -0800 (PST) X-Received: by 10.68.136.167 with SMTP id qb7mr2990180pbb.155.1425440704513; Tue, 03 Mar 2015 19:45:04 -0800 (PST) Original-Received: from na01-bn1-obe.outbound.protection.outlook.com (mail-bn1on0145.outbound.protection.outlook.com. [157.56.110.145]) by mx.google.com with ESMTPS id bq3si2927536pdb.238.2015.03.03.19.45.04 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 03 Mar 2015 19:45:04 -0800 (PST) Received-SPF: pass (google.com: domain of gdr@microsoft.com designates 157.56.110.145 as permitted sender) client-ip=157.56.110.145; Original-Received: from DM2PR0301MB0912.namprd03.prod.outlook.com (25.160.217.142) by DM2PR0301MB0686.namprd03.prod.outlook.com (25.160.96.24) with Microsoft SMTP Server (TLS) id 15.1.93.16; Wed, 4 Mar 2015 03:45:03 +0000 Original-Received: from DM2PR0301MB0911.namprd03.prod.outlook.com (25.160.217.141) by DM2PR0301MB0912.namprd03.prod.outlook.com (25.160.217.142) with Microsoft SMTP Server (TLS) id 15.1.99.14; Wed, 4 Mar 2015 03:45:01 +0000 Original-Received: from DM2PR0301MB0911.namprd03.prod.outlook.com ([25.160.217.141]) by DM2PR0301MB0911.namprd03.prod.outlook.com ([25.160.217.141]) with mapi id 15.01.0099.004; Wed, 4 Mar 2015 03:45:01 +0000 Thread-Topic: [std-proposals] An implementation of enhanced auto deduction and abbreviated template syntax using Clang Thread-Index: AQHQViR9WPFdJKanw0SwhTnX43nE7p0LruZv In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [73.35.173.108] x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:;SRVR:DM2PR0301MB0912;UriScan:; x-microsoft-antispam-prvs: x-exchange-antispam-report-test: UriScan:; x-exchange-antispam-report-cfa-test: BCL:0;PCL:0;RULEID:(601004)(5005006);SRVR:DM2PR0301MB0912;BCL:0;PCL:0;RULEID:;SRVR:DM2PR0301MB0912; x-forefront-prvs: 0505147DDB x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(979002)(6009001)(199003)(24454002)(51704005)(189002)(377454003)(41574002)(106116001)(50986999)(36756003)(76176999)(92566002)(54356999)(33656002)(99286002)(19580395003)(82746002)(19580405001)(62966003)(77156002)(86612001)(2950100001)(102836002)(66066001)(40100003)(122556002)(46102003)(83716003)(87936001)(2900100001)(86362001)(15975445007)(2656002)(110136001)(104396002)(491001)(969003)(989001)(999001)(1009001)(1019001);DIR:OUT;SFP:1102;SCL:1;SRVR:DM2PR0301MB0912;H:DM2PR0301MB0911.namprd03.prod.outlook.com;FPR:;SPF:None;MLV:ovrnspm;PTR:InfoNoRecords;A:1;MX:1;LANG:en; received-spf: None (protection.outlook.com: microsoft.com does not designate permitted sender hosts) X-MS-Exchange-CrossTenant-originalarrivaltime: 04 Mar 2015 03:45:01.3922 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM2PR0301MB0912 X-Microsoft-Antispam: BCL:0;PCL:0;RULEID:;SRVR:DM2PR0301MB0686; X-OriginatorOrg: microsoft.onmicrosoft.com X-Original-Sender: gdr@microsoft.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of gdr@microsoft.com designates 157.56.110.145 as permitted sender) smtp.mail=gdr@microsoft.com; dmarc=pass (p=NONE dis=NONE) header.from=microsoft.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:16679 gmane.comp.lang.c++.isocpp.general:4951 Archived-At: Should we declare "auto f(auto) -> auto" an excess in sophism? -- Gaby > On Mar 3, 2015, at 6:39 PM, Faisal Vali wrote: > > In the hopes of soliciting constructive feedback, if anyone has the > time or the interest to play with a patched up Clang that implements > enhanced auto deduction & abbreviated template syntax from the > concepts ts, here it is: > > https://github.com/faisalv/clang/tree/enhanced-auto-c%2B%2B1z . > > The last line of the README file tells you the subversion revision of > LLVM to use. > > For examples of test cases that successfully compile, please refer to: > -- https://github.com/faisalv/clang/blob/enhanced-auto-c%2B%2B1z/test/CXX/auto/cxx1z-auto-vars-generalized.cpp > -- https://github.com/faisalv/clang/blob/enhanced-auto-c%2B%2B1z/test/CXX/auto/cxx1z-abbreviated-templates.cpp > > I would certainly appreciate the feedback! > > 1) Enhanced-Auto Deduction: > > pair f() { return make_pair([] { }, [] { }); } > vector v = vector(); > > 2) Abbreviated Template Syntax: > void f(auto) <=> template void f(T); > > > A few, perhaps not so obvious or interesting, technicalities: > > a) The equivalence of templates when it comes to trailing return > types in function pointer parameters is based on the order of the > 'auto' that signifies a placeholder, not just the appearance of an > auto in the declaration-specifier of a parameter: > > template void f( R(P) ); // #1 > template void f( R(P) ); // #2 (order of > templ-params flipped) > > template void f( auto (P)->R); // equivalent to > #1, not abbreviated. > void f(auto(auto)); // equivalent to #1 > void f(auto (auto) -> auto); // equivalent to #2 > // the trailing return type auto > // identifies a > template parameter > template void f(R(auto); // equivalent to #1 > template void f(auto(P)); // equivalent to #2 > > b) variadic auto > Once an ellipsis is seen as part of the declarator, all contained > auto placeholders get transformed into parameter packs. > void f(auto (*...)(auto) -> std::tuple...>); > Note there are 4 deducible template parameter packs above. > > c) multi abbreviated template declarations > void f(auto), g(auto); > are allowed - the above declares two function templates. > > d) template aliases desugar their types *after* each auto has been > identified as a placeholder (and so must be deduced) > > template using Int = int; > Int i = 3; // Is an error, auto must be deducible. > > e) generic lambda's as default arguments work with abbreviated template syntax: > void f(int (*)(int) = [](auto a) { return a; }, auto b = decltype(b){}); > f(); // OK > > f) variable templates and enhanced auto deduction interact as expected: > template pair (*vfp)(auto...) = [](T t1, T* t2) > { return make_pair(t1, t2); }; > > Thanks! > Faisal Vali > > -- > > --- > 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/. > -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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