220 3598 article Path: news.gmane.org!not-for-mail From: morwenn29@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: "break break ;" etc. to break out of nested loops Date: Sat, 6 Apr 2013 02:23:01 -0700 (PDT) Lines: 137 Approved: news@gmane.org Message-ID: References: <1f964e4b-2762-43b8-85e5-41392926b07a@isocpp.org> <515FC3B0.2090803@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_2600_9437091.1365240181315" X-Trace: ger.gmane.org 1365274122 8506 80.91.229.3 (6 Apr 2013 18:48:42 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 6 Apr 2013 18:48:42 +0000 (UTC) Cc: Tony V E To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC2ZP4V74IFBB56S76FAKGQEYNHR6HQ@isocpp.org Sat Apr 06 20:48:43 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qc0-f198.google.com ([209.85.216.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UOXf6-0001Bx-Hw for gclcip-std-proposals@m.gmane.org; Sat, 06 Apr 2013 20:16:24 +0200 Original-Received: by mail-qc0-f198.google.com with SMTP id v20sf6159646qcm.1 for ; Sat, 06 Apr 2013 11:16:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-received:x-beenthere:x-received:date:from:to:cc:message-id :in-reply-to:references:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-google-group-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=ghAMZfWeicb4ftYckpCAOpwlFvNAnDTN5MRKjvH31yI=; b=LBgAmrGp/NsTRv7j6eOXxGu/uM4OHe3NYqrAdNFEcMgiwkfIoXqHQcp8uNbUpeG2rQ UFTPkbt1EDVE1oIeaUVeZZgt6nsjcspgkG22zXzEzFAqjG54zy9/UYKVqdOZvg6tp21F 63ivuaHt7AE+neuowFojcPz8xz8S6h3LJXWvRYZkuSmFRH3uhjn2HpECjMNP+eMWSvkA 0wFxhz4sF43Nocq8DaItY1EyDaV1zgkJeryTpVveSzUja1kQxB18WJ5pA4eAVtGc9s64 A2vR7Df8KTQ+W8xEL2ZFekuMWRRtGCY8LPa/aQadGEpkwFl5eCyn8uSrfsU51YywvsLB jBvw== X-Received: by 10.224.172.200 with SMTP id m8mr924214qaz.0.1365240183807; Sat, 06 Apr 2013 02:23:03 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.98.101 with SMTP id eh5ls2264132qeb.95.gmail; Sat, 06 Apr 2013 02:23:02 -0700 (PDT) X-Received: by 10.49.85.106 with SMTP id g10mr1240255qez.13.1365240182095; Sat, 06 Apr 2013 02:23:02 -0700 (PDT) In-Reply-To: <515FC3B0.2090803@gmail.com> X-Original-Sender: morwenn29@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:3598 Archived-At: ------=_Part_2600_9437091.1365240181315 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Le samedi 6 avril 2013 08:41:52 UTC+2, Chip Salzenberg a =E9crit : > > On 4/5/2013 3:23 PM, Tony V E wrote:=20 > > label: for (;;)=20 > > {=20 > > break label;=20 > > }=20 > > Yes, please; if this must be done, this is the way. It's one of the=20 > things that's actually worth borrowing from Perl. The label is=20 > semantically useful, and not brittle if another level is added. Thus:=20 > > line:=20 > while (cin >> s) {=20 > ...=20 > if (COND) continue line;=20 > ...=20 > } > =20 That seems to be the only viable way to go for this kind of problem. The= =20 break 1, break 2, break 3, etc... is easy to understand but, even as a=20 compile-time constant, I dont want to imagine what could be done with such= =20 a construct (well, I don't want to know, but never see it in real code): template void foobar() { for (...;...;...) { for (...;...;...) { for (...;...;...) { break N; // sit down and enjoy the complexity as if=20 there was no tomorrow } } } } Well, this kind of problems will never be encountered with a labeled break.= =20 But the label break is more verbose is the sense we need to label name. In most of the cases, putting the nested loops in a function and using=20 return is enough. If you want to read some more things about those breaks, there has been a= =20 proposal for Python: http://www.python.org/dev/peps/pep-3136/ It has been rejected, the reasons are included. That could be a good thing= =20 to read. --=20 ---=20 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 e= mail 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-proposa= ls/?hl=3Den. ------=_Part_2600_9437091.1365240181315 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Le samedi 6 avril 2013 08:41:52 UTC+2, Chip Salzenberg a =E9crit :On 4/5/2013 3:23 PM, Tony V E wrot= e:
> label: for (;;)
> {
>    break label;
> }

Yes, please; if this must be done, this is the way.  It's one of t= he
things that's actually worth borrowing from Perl.  The label is
semantically useful, and not brittle if another level is added.  T= hus:

    line:
      while (cin >> s) {
          ...
          if (COND) continue line;
          ...
      }
 
 That= seems to be the only viable way to go for this kind of problem. The break = 1, break 2, break 3, etc... is easy to understand but, even as a compile-ti= me constant, I dont want to imagine what could be done with such a construc= t (well, I don't want to know, but never see it in real code):

 = ;   template<unsigned N>
    void foobar(= )
    {
        for= (...;...;...) {
         &= nbsp;  for (...;...;...) {
      &nbs= p;         for (...;...;...) {
&= nbsp;           &nbs= p;       break N; // sit down and enjoy the c= omplexity as if there was no tomorrow
     &nbs= p;          }
  &= nbsp;         }
  &nbs= p;     }
    }

Well, this kind= of problems will never be encountered with a labeled break. But the label = break is more verbose is the sense we need to label name.
In most of the= cases, putting the nested loops in a function and using return is enough.<= br>
If you want to read some more things about those breaks, there has b= een a proposal for Python:
http://www.python.org/dev/peps/pep-3136/
I= t has been rejected, the reasons are included. That could be a good thing t= o read.

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