220 12075 <53D28931.3020501@gmx.de> article Path: news.gmane.org!not-for-mail From: Jan Herrmann Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Variadic catch Date: Fri, 25 Jul 2014 18:43:29 +0200 Lines: 95 Approved: news@gmane.org Message-ID: <53D28931.3020501@gmx.de> References: <53D270BF.5010906@gmx.de> <3f9efef6-04ec-47d7-807e-0d695bb2eba7@isocpp.org> <9E8291EE-CD67-4772-A364-0929FD18E295@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed X-Trace: ger.gmane.org 1406306625 26705 80.91.229.3 (25 Jul 2014 16:43:45 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 25 Jul 2014 16:43:45 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDJMREEMZMDRBOUSZKPAKGQE7T6D5JQ@isocpp.org Fri Jul 25 18:43:39 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-la0-f70.google.com ([209.85.215.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XAiao-0001Jc-Ti for gclcip-std-proposals@m.gmane.org; Fri, 25 Jul 2014 18:43:38 +0200 Original-Received: by mail-la0-f70.google.com with SMTP id mc6sf3282851lab.9 for ; Fri, 25 Jul 2014 09:43:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :subject:references:in-reply-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; bh=n39Fv28WLgExkwkQvH7C1LQE8HuPMr8K+4X0bFtTVrg=; b=d1/tQb0V2LRCeYx3pCEsyPnDX1TqOj9lTCa/X86Pu8J6lkE8g1e9QV4t0lfwubn2Cs c2edyg9SIlecOE5dAEsSlH89EvZhzKgnQiLUzdqLRpFTfRGDBfJH1o2AHMo691FF0h/e 5jdJiwlvkJx/vxZ/U5eHv08uyYIc8XQLCCihILLVIl+oGBBaPrdhBgYMQna3CkSe6BxX F7D8Ash14q0gP4G0r2F0UVCqmVHBx0AXfPfDvTyhpjLNGeA75dYwgwxNCGq2ka9gelPo 2SGzS96XZnkyFuM9UdvVOCLKdVpQuvRHuxKY52w1b/cb7wqLxxaLqY+BDvmofKGF096o zGwA== X-Gm-Message-State: ALoCoQl7Nf63pK9G5aHqCjzwf7WuJ5t5DchLdynCTnQPZ1CFd3A/Jr1iubqiB1p7toLksT4T302J X-Received: by 10.180.36.38 with SMTP id n6mr588975wij.0.1406306618652; Fri, 25 Jul 2014 09:43:38 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.77.41 with SMTP id p9ls121331wiw.17.canary; Fri, 25 Jul 2014 09:43:37 -0700 (PDT) X-Received: by 10.180.35.36 with SMTP id e4mr7035726wij.12.1406306617831; Fri, 25 Jul 2014 09:43:37 -0700 (PDT) Original-Received: from mout.gmx.net (mout.gmx.net. [212.227.17.22]) by mx.google.com with ESMTPS id mc8si18982821wjb.66.2014.07.25.09.43.37 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 25 Jul 2014 09:43:37 -0700 (PDT) Received-SPF: pass (google.com: domain of jherrmann79@gmx.de designates 212.227.17.22 as permitted sender) client-ip=212.227.17.22; Original-Received: from [192.168.1.2] ([84.184.1.176]) by mail.gmx.com (mrgmx103) with ESMTPSA (Nemesis) id 0LjJCt-1WePB80Cch-00dZtg for ; Fri, 25 Jul 2014 18:43:37 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.0 In-Reply-To: X-Provags-ID: V03:K0:Xl+QmceOj4dmPTCsSCvNNssUdDr93c+biSJfXob94VV2nHuEvAQ uNltFFAZBS3HdCPpf83j9Jf/d+GydwbzJXDUuey4vhMDoVHTOX9lnHencb3ZpQaQeElc1oo jnsqen5QjJoI+W700m7t7FnKdFVItJVw4WN45z6MANe/cX0uMN/z0E6slHQ+8Hzw99WEH/x uFiDF8VNOIUSQ9oxfY34A== X-Original-Sender: jherrmann79@gmx.de X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of jherrmann79@gmx.de designates 212.227.17.22 as permitted sender) smtp.mail=jherrmann79@gmx.de 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:12075 Archived-At: On 25.07.2014 18:04, Ville Voutilainen wrote: > On 25 July 2014 18:44, David Krauss wrote: >> >> On 2014-07-25, at 11:36 PM, Jeaye Wilkerson wrote: >> >>> Yes, the body of the catch block would need to be generic for each type, but, as with any generic API within the generic paradigm, that doesn't mean they should share a common base; they share a common public interface. >> >> That's just a bad design. The language shouldn't support it. Just because it's possible doesn't mean it's OK. > > What's bad design? A library providing multiple exception types that > do not form a hierarchy? > I disagree. There's nothing bad about it. Now, whether we need to > provide a way to generate > the code to catch all those different exception types and run the same > code on all of them is > a different matter. > > Work-arounds certainly seem to incur unfortunate costs - using a > variable function template > that re-throws and catches a specific type will lead to one re-throw > per every type in the pack, > as opposed to a single throw that this extension proposal would have. > The first version has another background (it can be used more dynamically). I have a second version which needs some polishing but should show my ideas ( http://coliru.stacked-crooked.com/a/0420ce9ae0180306 ): #include #include #include template struct excpected_exception; template struct excpected_exception { void operator()(Fun f, ExceptionHandler eh) { try { excpected_exception{}(f, eh); } catch (Ex1 const& ex) { eh(ex); } } }; template struct excpected_exception { void operator()(Fun f, ExceptionHandler) { f(); } }; template void expect_exception(F f, Eh eh) { excpected_exception{}(f, eh); } struct MyEh { template void operator()(Ex&& ex) const { std::cerr << ex.what() << "(" << typeid(ex).name() << ")" << std::endl; } }; int main() { expect_exception([&]{throw std::runtime_error("Hello");}, MyEh{}); expect_exception([&]{throw std::logic_error("World");;}, MyEh{}); return 0; } The main problem with this version is that exceptions have to be sorted to bring derived exceptions to front and eventually to bring often catched exceptions to front. This has to be standardized as well. Jan Herrmann -- --- 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/. .