220 33577 article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Catch block for multiple exceptions Date: Thu, 3 Aug 2017 18:25:02 -0700 (PDT) Lines: 103 Approved: news@gmane.org Message-ID: References: <4126837.jZlGhgVnua@tjmaciei-mobl1> <54580edb-4a76-4241-b5c8-19ccbc1a562e@isocpp.org> <4c872807-7d50-4b58-bbb5-595a8bac1246@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_291_334164219.1501809902281" X-Trace: blaine.gmane.org 1501809906 11175 195.159.176.226 (4 Aug 2017 01:25:06 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 4 Aug 2017 01:25:06 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBB3UZR7GAKGQECHHAAKY@isocpp.org Fri Aug 04 03:25:02 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f71.google.com ([209.85.214.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ddRMJ-0002RT-0I for gclcip-std-proposals@m.gmane.org; Fri, 04 Aug 2017 03:24:59 +0200 Original-Received: by mail-it0-f71.google.com with SMTP id 7sf3498571ita.0 for ; Thu, 03 Aug 2017 18:25:04 -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: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; bh=2i9yPok07O8ZGzX08YvEeV4xpequPKLWXCkmhAoDrAA=; b=ojOYX0GB7P07RCQychvhkFULBPUXPXDmpS0RD5nlIoN5NPPwcXrrZv3RkrgOjJ1vST uM+GsvYj9PI6yVT+znPZLOcpKhSZF++Hr2XMA7kJ6rfvhoSDo4ToFnyN3zFLFdj2Y9De 0WjC/1na3OnSddqMABKs+A4WXoq/lkOKFI0otlQRX8iByNb+YlY2ioVJv0laQf33pEtL C2cKqCgtdu2cVSMMYVi+KuLmqwE4Zzc5SObUFUKd2zTobuhcF2BACgnx8F2zMzoXwC/u lerSTb8Gb7oyLpjcSUQN5zqYDeuqVzQJNZUSPNYJ/CmoMb4NmbUfAy2Ym6ynywWqYDoX T07g== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=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; bh=2i9yPok07O8ZGzX08YvEeV4xpequPKLWXCkmhAoDrAA=; b=RXoxy2al4mKXL7NbOHqvdGM7Cls+y8JZIlKhpMZzXgHWXtD/fPtEYMwierDwVoi2bd UFJunAJzSRUkotfoOXRWedJjg4tQlhK3FDajEjY7slIsUbzG9BrP/8S0jyMb6g7OW1fb /LiJShgjBbvJZN/xTJ+R6ltEQNtXppDU5p5m8mIwnW0rU44l3edHAWyQzWd2hmAFfZqd kW/J/MUJO4/TZynbh/h8SRNxQ00us167r7QfCwiz7fVKXcQpwiBRqVieq7bKhv9j0Ekf ArWETQaJObQnqKEIN2J5G+zQnsg8M2YfemvoqvJtbEF4BW6mDkPCXcMWFGZe4bFFspU8 D4mA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; 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:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=2i9yPok07O8ZGzX08YvEeV4xpequPKLWXCkmhAoDrAA=; b=LAn80sNe4c0eK3cyq99879KgKzEfEtjNaJnhTI3VJFVJWsBoCDa43RldV0FSgbYQU4 5DOwCfKydYLpfbdPvgWfPWXxUX2HuA/LXOSWOavIJSYvPnU1Hf2M70v+aW+hmKynh3xO l5W0ppp4sHUnAlNo0oVFD2sCBohzDGuAhMCgx7l9Xoy37gaEFy9oLgWx1UsZst+WIZoc nWyV5Yi7MgLe4O5Letziwr8jJ1qj/TwTHcsCLH0DZksg0GCs5XtJN91tftMoPyQN+AO0 CI/gmqx94bYJBtx6XPD7v02PWiITx+IJW57VZQHFzqlpOzSsEZwoMKK6CUJ+Hv5KgAjD hJCA== X-Gm-Message-State: AHYfb5gHzh/hJeWyCEEUxCJ01PXB7PkNSG/INC9Mtcblr1lJQ78lJjlN 8I57Kzx1dMVRQBFv X-Received: by 10.107.17.165 with SMTP id 37mr554237ior.106.1501809904130; Thu, 03 Aug 2017 18:25:04 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.249.129 with SMTP id l123ls755359ith.14.gmail; Thu, 03 Aug 2017 18:25:02 -0700 (PDT) X-Received: by 10.31.142.14 with SMTP id q14mr3341vkd.19.1501809902737; Thu, 03 Aug 2017 18:25:02 -0700 (PDT) In-Reply-To: X-Original-Sender: jmckesson@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:33577 Archived-At: ------=_Part_291_334164219.1501809902281 Content-Type: multipart/alternative; boundary="----=_Part_292_1808809100.1501809902282" ------=_Part_292_1808809100.1501809902282 Content-Type: text/plain; charset="UTF-8" On Thursday, August 3, 2017 at 8:14:00 PM UTC-4, Ville Voutilainen wrote: > > On 4 August 2017 at 02:17, Arthur O'Dwyer > wrote: > >> Note that both of our solutions suffer from the problem that the code > >> in the catch-clause > >> cannot break, continue, goto or return like plain code could. An > >> if-else chain of any_casts > >> from exception_ptr would be able to do that. > > > > > > Do you think LEWG would be amenable to a proposal to make std::any_cast > an > > all-purpose "type-un-erasing" mechanism in C++2a? > > Way to jump the gun. I doubt it, because it doesn't make sense to have > one name for > different things. However, unerasing the type of an any and an > exception_ptr are > exactly the same. > Not really. The key difference being that `any_cast` typically returns a copy of the object, while the exception pointer cast would return a pointer. It should also be noted that the exception pointer cast needs to be able to be cast to the actual exception type or any of its base classes. So if the exception derives from `std::exception`, then doing `exception_cast` should work. `any_cast` very much does not have those semantics. -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/caf74994-b217-4108-80ce-664e64510e34%40isocpp.org. ------=_Part_292_1808809100.1501809902282 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Thursday, August 3, 2017 at 8:14:00 PM UTC-4, V= ille Voutilainen wrote:
On 4 Au= gust 2017 at 02:17, Arthur O'Dwyer <arthur....@gmail.com> wrote:
>> Note that both of our solutions suffer from the problem that t= he code
>> in the catch-clause
>> cannot break, continue, goto or return like plain code could. = An
>> if-else chain of any_casts
>> from exception_ptr would be able to do that.
>
>
> Do you think LEWG would be amenable to a proposal to make std::any= _cast an
> all-purpose "type-un-erasing" mechanism in C++2a?

Way to jump the gun. I doubt it, because it doesn't make sense to h= ave
one name for
different things. However, unerasing the type of an any and an exceptio= n_ptr are
exactly the same.

Not really. The key differen= ce being that `any_cast` typically returns a copy of the object, while the = exception pointer cast would return a pointer.

It should also be not= ed that the exception pointer cast needs to be able to be cast to the actua= l exception type or any of its base classes. So if the exception derives fr= om `std::exception`, then doing `exception_cast<std::exception>` shou= ld work. `any_cast` very much does not have those semantics.

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/caf74994-b217-4108-80ce-664e64510e34= %40isocpp.org.
------=_Part_292_1808809100.1501809902282-- ------=_Part_291_334164219.1501809902281-- .