220 18372 article Path: news.gmane.org!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Thoughts on Exceptions, Expected, and Error Handling Date: Wed, 03 Jun 2015 13:36:03 -0400 Lines: 52 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 1433353010 18951 80.91.229.3 (3 Jun 2015 17:36:50 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 3 Jun 2015 17:36:50 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCO5FYHBU4ERBI7WXSVQKGQEQTXWLLI@isocpp.org Wed Jun 03 19:36:37 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wi0-f198.google.com ([209.85.212.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Z0Cai-0000XI-VA for gclcip-std-proposals@m.gmane.org; Wed, 03 Jun 2015 19:36:37 +0200 Original-Received: by wibbk2 with SMTP id bk2sf7134517wib.2 for ; Wed, 03 Jun 2015 10:36:36 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:to:from:subject:date:lines:message-id:references :mime-version:content-type:user-agent: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; bh=mJkFsyH5Qbif0rFc0lXvFMAagEPzU4VfyAIm1cJqBB4=; b=IYHLk4KAjeqSwV0eYYVwsFiIF7uxA6HlWq5z8sPP2EdVF1mZPGmUmDICf3zo3FCh+v /64JrgAltPTCEGthYrTpUE9U/vmF384AICrkKSckeb6zwGlQjqi4VX6yI5kiEE85/TWB iVAv2QxIv7jx4ZEfZixykhtzzqiUDqHrtKgc5qupG+mDb0bMnH8o1mCbfVz9K9sKG9bO Rjssp2QF4GxXi7zH2z1iTGI1VsIXIua+zXo8vvgLUiJahXlbwJKJ/TwYsXTG3GpaqIN2 9LqHf9C47f0FYYDDb11HoA+EesGEcIlmdczYJHQ5wT9MU0JmQWH7FDHWlNhzPR6HdmLq lEUw== X-Gm-Message-State: ALoCoQk2bXPKByZ8LUWe6oSsxbvpdVSG3YiBeUMKMGWICGdjm7xldJjmA0JuU7iHoqhEKsYma+lN X-Received: by 10.112.26.5 with SMTP id h5mr31907827lbg.4.1433352996507; Wed, 03 Jun 2015 10:36:36 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.28.4 with SMTP id x4ls104550lag.40.gmail; Wed, 03 Jun 2015 10:36:35 -0700 (PDT) X-Received: by 10.112.137.1 with SMTP id qe1mr32411549lbb.22.1433352995126; Wed, 03 Jun 2015 10:36:35 -0700 (PDT) Original-Received: from plane.gmane.org (plane.gmane.org. [80.91.229.3]) by mx.google.com with ESMTPS id r2si4591599lar.46.2015.06.03.10.36.35 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 03 Jun 2015 10:36:35 -0700 (PDT) Received-SPF: pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) client-ip=80.91.229.3; Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1Z0CaY-0000OR-BF for std-proposals@isocpp.org; Wed, 03 Jun 2015 19:36:26 +0200 Original-Received: from tripoint.kitware.com ([66.194.253.20]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 03 Jun 2015 19:36:26 +0200 Original-Received: from mw_triad by tripoint.kitware.com with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 03 Jun 2015 19:36:26 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 43 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: tripoint.kitware.com User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 In-Reply-To: X-Original-Sender: mw_triad@users.sourceforge.net X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) smtp.mail=gclcip-std-proposals@m.gmane.org 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:18372 Archived-At: On 2015-06-03 01:09, Nicol Bolas wrote: > However, everything that `error_condition` can do is based purely on the > type of `error_category` it uses and an integer. Now, consider parsing > integers. If a parse error occurs, the parsing system knows a lot of very > useful information about it. It knows how many characters it successfully > read. It knows exactly which character caused that error. And so forth. > > All of that information is *lost* when you reduce the error to a number. Actually, if the caller passed in an output parameter to receive the end pointer (which would not be an unusual use case), the caller would still be able to construct your better exception. I'm not convinced this is an argument against 'expected', though it sounds like a reasonable argument against 'expected' in some contexts that I think deserves consideration. > But if you start throwing around an `expected` If you're storing big_giant_object inline rather than as some sort of smart pointer, you're doing it wrong :-). (And indeed, since you're storing it *by value*, and one or the other is AFAIK required, in this case it might make sense for expected itself to store big_giant_object as a pointer, whose nullness or not indicates if it has an int or a big_giant_object.) > And then there are things that `expected` flat-out cannot handle or handles > very poorly. > > The first is any function that doesn't return a value. Oh yes, > `expected` exists. But it would be rather... foolish to expect > everyone to do that. Uniformly. > > The same applies to any function that returns a value that most users will > drop on the floor. Neither of these are cases that 'expected' is meant to solve, and it's clearly the wrong tool in both cases. These - especially the second - are cases where you want a 'checked result' type if just throwing in the first place is not an option. -- Matthew -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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