220 33541 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: Wed, 2 Aug 2017 11:47:28 -0700 (PDT) Lines: 97 Approved: news@gmane.org Message-ID: References: <4126837.jZlGhgVnua@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_3380_1459456279.1501699649030" X-Trace: blaine.gmane.org 1501699651 6077 195.159.176.226 (2 Aug 2017 18:47:31 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 2 Aug 2017 18:47:31 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBQN4RDGAKGQEWYXWKHQ@isocpp.org Wed Aug 02 20:47:26 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f199.google.com ([209.85.217.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dcyg1-0001D7-0y for gclcip-std-proposals@m.gmane.org; Wed, 02 Aug 2017 20:47:25 +0200 Original-Received: by mail-ua0-f199.google.com with SMTP id x24sf19699023uah.7 for ; Wed, 02 Aug 2017 11:47:31 -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=9oa6Wor6+XGfVWQLrHHus38RU7eUlBzA4kni5xMWhBc=; b=cClm6jFcwHL0Y8PpoaNJ9dlfi64fpSqtLsV3uVLg1H38BIuErUQ+cNMdCZONrBl3R/ UIrDjEiCKGKgeBCFomf3dmIsDbnC9b7TsdTCZ1LNGUaXBBEhd90AUjOV77s6wjpEggF7 YH36qGMi76T5qKs2C14De6uRwnezM7uKsRCHonp5HZwrkPfAw7k/e2Y3PQbhJjutJBfc SGBuOy7Yo0Eowu+FFN61cYiznf/+cBSoDoCmJFztVkjSE9p3lW3+U26QryOLRKpOguD3 lSNpukn0KcVjFq/Dyk7yTzw9qbi8uqEzd4bFlK/kRFS0LN6h+TlZZC2C4gyX3R9n7UUi 8Yog== 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=9oa6Wor6+XGfVWQLrHHus38RU7eUlBzA4kni5xMWhBc=; b=WrE8r3wJgcRlaekySH1kvXB97q7ASY3o++q31yuV4l6kG1dvQ0dZEyRBzlQeDVOHp+ MqRxgy7paL+EE8vzuBFu9iD7QrBRCcrqQGz4kT/cGCPXoaz4dSsW7EACDpAk7Nu7dl+x 07bZZd7pdak8peVsDvyN7nByc0axIlcDzYFuZL6ldNlDPbxH85F61PCTIokDaJvDaXmB 5Bf1gBne5mvHB0wC3qrZENFqoQXVZrhwjFYf/pcw4DezDJtG4hqbdbcbm4a8xhECxQ40 0iJpgLtga67DB5h9UfvCHac6m+ZvT0sPpOJMXwpX1z5F/xpHb5BsFyWmHJQNDc4ixK9t V4nQ== 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=9oa6Wor6+XGfVWQLrHHus38RU7eUlBzA4kni5xMWhBc=; b=JL+gz2yhPGBkqwmxqPhuTIl6yUPEncu2rlJLAz9yRViVYMDK0QHfeGZdMJhCFhGJsL 8DudC+RFuE+7Oc3389Qs369+XW75xYo5vEGv80v9YnbiNPHFpDc7bX1NmU1BfeqrCFlG xGTUWKWybLkY+XtseEd3L2RC0DN1p9HKG0xKM3JBJOqby2kocpIvfF97h6lkJSJNnchZ DJyKLbmK9LbaAOGNxP7fFp/KNPHqmV3XKjQGkmu+Bt+PsRj+6DSubZx9vfCecItNaihd f6OBBx8LRufBczGgNgMmsgIgMSkBBzVzheKoBlKIIrL2FNey0woPlqFLrMTJCi/Zaw2b 3Tsg== X-Gm-Message-State: AIVw113twTdWiaDLk0ptn8aeHeKKxlcEao6NI+7xhTHZoYyD2PnwT6ta kDDeXgC2FnR1yzDf X-Received: by 10.31.179.83 with SMTP id c80mr14557602vkf.60.1501699650838; Wed, 02 Aug 2017 11:47:30 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.146.87 with SMTP id u84ls7156iod.11.gmail; Wed, 02 Aug 2017 11:47:29 -0700 (PDT) X-Received: by 10.31.142.14 with SMTP id q14mr72378vkd.19.1501699649443; Wed, 02 Aug 2017 11:47:29 -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:33541 Archived-At: ------=_Part_3380_1459456279.1501699649030 Content-Type: multipart/alternative; boundary="----=_Part_3381_1107108792.1501699649030" ------=_Part_3381_1107108792.1501699649030 Content-Type: text/plain; charset="UTF-8" On Wednesday, August 2, 2017 at 2:40:35 PM UTC-4, Ville Voutilainen wrote: > > On 2 August 2017 at 21:05, Ricardo Fabiano de Andrade > > wrote: > > Hum, a template... bikeshedding an alternate syntax: > > > > catch(auto& e) { > > ... do something > > } > > > Boo hiss. Let's just write a solution with the toys C++17 gives us. > That is a truly hideous stream of code. But I imagine that this situation is so rare that a "hideous stream of code" is probably not a terrible idea for a solution. However, I think a small library feature could help make it less painful. Right now, we have `current_exception`, which gives us an `exception_ptr`, which is completely type-erased. We could give `exception_ptr` a way to un-erase the type. After all, the implementation has to have that type somewhere, since we can throw and re-catch it. So perhaps an `any_cast`-like mechanism, that returns either `nullptr` or a pointer to the exception object. Only it should work as if it were a `dynamic_cast`. Then, we could implement an `exception_visitor` that takes a sequence of types and tries them, in order. -- 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/aec5f733-d43e-4d75-b001-0a0e9d49217f%40isocpp.org. ------=_Part_3381_1107108792.1501699649030 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Wednesday, August 2, 2017 at 2:40:35 PM UTC-4, = Ville Voutilainen wrote:
On 2 A= ugust 2017 at 21:05, Ricardo Fabiano de Andrade
<ricardofabi...@gmail.com> wrote:
> Hum, a template... bikeshedding an alternate syntax:
>
> catch<exceptionA, exceptionB, exceptionC>(auto& e) {
> =C2=A0... do something
> }


Boo hiss. Let's just write a solution with the toys C++17 gives us.

That is a truly hideous stream of code. But I ima= gine that this situation is so rare that a "hideous stream of code&quo= t; is probably not a terrible idea for a solution.

However, I think = a small library feature could help make it less painful. Right now, we have= `current_exception`, which gives us an `exception_ptr`, which is completel= y type-erased. We could give `exception_ptr` a way to un-erase the type. Af= ter all, the implementation has to have that type somewhere, since we can t= hrow and re-catch it.

So perhaps an `any_cast`-like mechanism, that = returns either `nullptr` or a pointer to the exception object. Only it shou= ld work as if it were a `dynamic_cast`. Then, we could implement an `except= ion_visitor` that takes a sequence of types and tries them, in order.
=

--
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/aec5f733-d43e-4d75-b001-0a0e9d49217f= %40isocpp.org.
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