220 18419 article Path: news.gmane.org!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Thoughts on Exceptions, Expected, and Error Handling Date: Fri, 5 Jun 2015 09:01:22 -0700 (PDT) Lines: 99 Approved: news@gmane.org Message-ID: References: <1d83a5df-f8b1-41fc-a197-319825b5436d@isocpp.org> <97c9b3aa-44b4-4a63-92a0-a571628b0735@isocpp.org> <303e5cc6-8a3e-4063-880e-eac448ec0dc6@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1263_130719500.1433520082761" X-Trace: ger.gmane.org 1433520103 19060 80.91.229.3 (5 Jun 2015 16:01:43 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 5 Jun 2015 16:01:43 +0000 (UTC) Cc: mw_triad@users.sourceforge.net To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCEKFTV6ZUMBBU4PY6VQKGQEOFPPGWA@isocpp.org Fri Jun 05 18:01:42 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wg0-f71.google.com ([74.125.82.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Z0u3g-0002Ur-U0 for gclcip-std-proposals@m.gmane.org; Fri, 05 Jun 2015 18:01:24 +0200 Original-Received: by wgme6 with SMTP id e6sf18392107wgm.3 for ; Fri, 05 Jun 2015 09:01:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:content-type:x-original-sender:reply-to:precedence :mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=sARnhuPueorbjHBKeWdgLn6/WrWejxFdHiiWBM4Vz+I=; b=ni/01RsHBj/Fw/KI74TTjNuRmMhF0i8lJr3zjRgkVfPHL6ojaBzE/PEFNHKomhG5EC jmrr6K4/vxSmfWCXGzHXhdfHLZUIm+gQnE08DVePmbd0oYRqdXs3DqJQxBFESPN4U0t0 /8bX6rdlcaw42+QXfGTXZX+RXeWUM7ochgHGdf8um1uUWhq6kfCe4K4mG8ICQv74ljNp 7Gv/nUR68KJr3y3FA/hUnXWUsBk3GXwMTnqkTeVFH4uaogedyA5ogA1h5otmxHOXCuy/ Xbw4+IvC9TnEZ7Vemi4QXNfnmSFsgyWlDtNXyqz2xXjEyZIFM71paERlqgnd2ED1Lsc/ jJzA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:content-type:x-original-sender :reply-to:precedence:mailing-list:list-id:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=sARnhuPueorbjHBKeWdgLn6/WrWejxFdHiiWBM4Vz+I=; b=jSS0Npbn18wqmpGRCC/kpi3wkLS7b/fD7vPdfItzDYL+XlNMMtJqikOkOZxeasXHil lPC49HTSBVZBzeCTc7Y5WOMM3irhqQD2s/IKJq/NkTEtRZbjCxk8/24T3qAiK8aTeGE2 Jsjpdc0glD5aT8tyvRRQjmoJwNWhGvMD46LtGmtPV24S+aF/nGWkaVu62ICxDaC3MPIs HDfJAdO5re02zInLrCBekbQyLEYlMVjaXtS2hsYiMr/H3Iqt2TqFvnvoQQ9qgqHxleSW pfrFJtixja05uGXDfnaNhd9/QfI0Y1qzbL0b6a0pwcJyVAuPF33j2nHNGbioEjJaA8wn JVdw== X-Gm-Message-State: ALoCoQnN6drzQ8HQflP01jhjoYD9YTkVeV2dnk9NaPPPW8xiW8DwYZfWB/pZ+NucRvmWY3Ydh7Tw X-Received: by 10.194.5.229 with SMTP id v5mr3828123wjv.0.1433520084436; Fri, 05 Jun 2015 09:01:24 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.16.178 with SMTP id 47ls1522580qgb.89.gmail; Fri, 05 Jun 2015 09:01:23 -0700 (PDT) X-Received: by 10.140.100.136 with SMTP id s8mr51908qge.2.1433520083192; Fri, 05 Jun 2015 09:01:23 -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:18419 Archived-At: ------=_Part_1263_130719500.1433520082761 Content-Type: multipart/alternative; boundary="----=_Part_1264_126865619.1433520082761" ------=_Part_1264_126865619.1433520082761 Content-Type: text/plain; charset=UTF-8 On Thursday, June 4, 2015 at 11:05:07 AM UTC-4, Matthew Woehlke wrote: > > On 2015-06-04 03:00, Nicol Bolas wrote: > > Exceptions are a sledgehammer; expected is a scalpel. Both are good > tools > > in their domain, yet you seem to be promoting the idea that everyone > should > > become a surgeon. > > ...I agree with this. I think we need expected, but I don't think we > should be promoting it as the One True Method for global error handling. > Developers should continue to use their preferred method for error > propagation. As much as possible, expected should be friendly to callers > that want to turn errors into exceptions. > You were doing so well, right up until the last sentence. The choice needs to be made by the caller, yes. But the choice should be made by calling a function that throws exceptions, not by calling some member of an `expected`. By then, you've already lost some information that the function had about the actual error. Oh, you can have `.value()` throw if it doesn't hold a value; that's fine. But throwing in such a case should not represent the same thing as the function actually throwing. It instead represents a caller of the `expected` version who didn't do what he was supposed to do. APIs should provide both, not simply rely on `expected` to throw for users who want exceptions. -- --- 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/. ------=_Part_1264_126865619.1433520082761 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Thursday, June 4, 2015 at 11:05:07 AM UTC-4, Ma= tthew Woehlke wrote:
On 2015-06= -04 03:00, Nicol Bolas wrote:
> Exceptions are a sledgehammer; expected is a scalpel. Both are goo= d tools=20
> in their domain, yet you seem to be promoting the idea that everyo= ne should=20
> become a surgeon.

...I agree with this. I think we need expected, but I don't think we
should be promoting it as the One True Method for global error handling= ..
Developers should continue to use their preferred method for error
propagation. As much as possible, expected should be friendly to caller= s
that want to turn errors into exceptions.

You = were doing so well, right up until the last sentence.

The choi= ce needs to be made by the caller, yes. But the choice should be made by ca= lling a function that throws exceptions, not by calling some member of an `= expected`. By then, you've already lost some information that the function = had about the actual error.

Oh, you can have `.value()` throw if it = doesn't hold a value; that's fine. But throwing in such a case should not r= epresent the same thing as the function actually throwing. It instead repre= sents a caller of the `expected` version who didn't do what he was supposed= to do.

APIs should provide both, not simply rely on `expected` to t= hrow for users who want exceptions.

--

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