220 35958 article Path: news.gmane.org!.POSTED!not-for-mail From: Jake Arkinstall Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: auto return proposal Date: Sun, 17 Dec 2017 19:54:41 +0000 Lines: 91 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="001a113adaa4c98ae805608e9a8d" X-Trace: blaine.gmane.org 1513540366 21779 195.159.176.226 (17 Dec 2017 19:52:46 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 17 Dec 2017 19:52:46 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDCZX3WUUQFRBAUX3PIQKGQE6TWYAUQ@isocpp.org Sun Dec 17 20:52:42 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ot0-f200.google.com ([74.125.82.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eQezJ-0005KI-RK for gclcip-std-proposals@m.gmane.org; Sun, 17 Dec 2017 20:52:42 +0100 Original-Received: by mail-ot0-f200.google.com with SMTP id u10sf7939893otc.21 for ; 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[209.85.220.41]) by mx.google.com with SMTPS id u184sor3976344oig.162.2017.12.17.11.54.42 for (Google Transport Security); Sun, 17 Dec 2017 11:54:42 -0800 (PST) Received-SPF: pass (google.com: domain of jake.arkinstall@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.202.213.76 with SMTP id m73mr12378356oig.79.1513540482073; Sun, 17 Dec 2017 11:54:42 -0800 (PST) Original-Received: by 10.168.69.140 with HTTP; Sun, 17 Dec 2017 11:54:41 -0800 (PST) Original-Received: by 10.168.69.140 with HTTP; Sun, 17 Dec 2017 11:54:41 -0800 (PST) In-Reply-To: X-Original-Sender: jake.arkinstall@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=GIgO9tMU; spf=pass (google.com: domain of jake.arkinstall@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=jake.arkinstall@gmail.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:35958 Archived-At: --001a113adaa4c98ae805608e9a8d Content-Type: text/plain; charset="UTF-8" On 17 Dec 2017 18:09, "Nicol Bolas" wrote: If the user passes an inappropriate `value`, then that's on them and you want UB to happen. I'm not sure on that. It almost seems like a perfect place for a Maybe monad. And if `T` is not default-constructible, then the only thing you can do is `throw` (or use something like `expected`). And what if you don't want to? What if you want the narrow contract? If you want a function that does return something useful iff the argument makes sense, that's THE use case of std::invalid_argument. This is a function that works all the time, 99% of the time. Perhaps a definite return or throw is one option. I can't see how your example is in any way made worse by adding a throw at the end, and at least the user finds out what they did wrong. Providing them with a program that seems to be running fine before it goes crazy at a later point isn't helpful to anyone. I certainly agree that giving the programmer the flexibility of making assumptions is useful, though, and I'm wondering if a keyword to allow non-returning branches would make sense. I don't have a particularly strong position on this, though. It makes sense to leave this to the discretion of the compiler writers if it's too controversial. -- 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/CAC%2B0CCN7mFF1hiPPyUetL0mNaOkrjkhpsSv2QxXBfUfLzVqK8g%40mail.gmail.com. --001a113adaa4c98ae805608e9a8d Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On 17 Dec 2017 18:09, "Nicol Bolas" <jmckesson@gmail.com> wrote:
=
If the user passes an inappr= opriate `value`, then that's on them and you want UB to happen.

<= div dir=3D"auto">I'm not sure on that. It almost seems like a perfect p= lace for a Maybe monad.

=
And if `T` is not default-constructible, then the= only thing you can do is `throw` (or use something like `expected`). And w= hat if you don't want to? What if you want the narrow contract?

If you want a function that does return something useful iff the = argument makes sense, that's THE use case of std::invalid_argument. Thi= s is a function that works all the time, 99% of the time.

Perhaps a definite return or throw is one= option. I can't see how your example is in any way made worse by addin= g a throw at the end, and at least the user finds out what they did wrong. = Providing them with a program that seems to be running fine before it goes = crazy at a later point isn't helpful to anyone.
=
I certainly agree that giving the programmer th= e flexibility of making assumptions is useful, though, and I'm wonderin= g if a keyword to allow non-returning branches would make sense. I don'= t have a particularly strong position on this, though. It makes sense to le= ave this to the discretion of the compiler writers if it's too controve= rsial.

--
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