220 3619 article Path: news.gmane.org!not-for-mail From: Benjamin Lindley Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: "break break ;" etc. to break out of nested loops Date: Sun, 7 Apr 2013 11:40:04 -0700 (PDT) Lines: 172 Approved: news@gmane.org Message-ID: References: <1f964e4b-2762-43b8-85e5-41392926b07a@isocpp.org> <51614514.2060103@bubblescope.net> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_2210_722238.1365360004986" X-Trace: ger.gmane.org 1365360012 1097 80.91.229.3 (7 Apr 2013 18:40:12 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 7 Apr 2013 18:40:12 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDI7THWOWMDRBB73Q2FQKGQE5M3ICPI@isocpp.org Sun Apr 07 20:40:14 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ve0-f199.google.com ([209.85.128.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UOuVc-00081s-Ae for gclcip-std-proposals@m.gmane.org; Sun, 07 Apr 2013 20:40:08 +0200 Original-Received: by mail-ve0-f199.google.com with SMTP id jw11sf8628687veb.2 for ; Sun, 07 Apr 2013 11:40:07 -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: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=pgxEBkSyYjRkIqdbWdIc+BYQN+7G6tiXY6XHX0Q0/js=; b=Fnvj/8xB7IcBZftgVXAtTQ5E2GMt+tmoVadPsJm/eOPJD10ZeSW3GeONKlIHMD4BKg nbFl+YHR2dTkhwDlgHCqFfFr+4wx7J1lkug/neceLu5GPu1Kf30oXKLbondBIzqRfqwa T7o8JyG3qLg79A72l3ld9IrJxzgW4eaj2FXycJIHrrGyFpSo7eMvWVF/7BNzrhvNXYGc vjxPKPgzvcFufb3R6KbLq1pJ3qUcLaiswP0Wq4kXI+sajV3UkZuXXifU+SmkUmUG3Zp2 GWab7r5QxnUOCXS0ahNCHNnCiHyoTohScrB6g3JTZO6/F9FUn4CcPETsKnFVHRtEgWYw 5EXw== X-Received: by 10.224.219.146 with SMTP id hu18mr4051814qab.3.1365360007426; Sun, 07 Apr 2013 11:40:07 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.3.99 with SMTP id b3ls2850676qeb.97.gmail; Sun, 07 Apr 2013 11:40:05 -0700 (PDT) X-Received: by 10.49.60.193 with SMTP id j1mr1240069qer.33.1365360005912; Sun, 07 Apr 2013 11:40:05 -0700 (PDT) In-Reply-To: <51614514.2060103@bubblescope.net> X-Original-Sender: benjameslindley@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:3619 Archived-At: ------=_Part_2210_722238.1365360004986 Content-Type: text/plain; charset=ISO-8859-1 On Sunday, April 7, 2013 5:06:12 AM UTC-5, Chris Jefferson wrote: > > On 05/04/13 20:23, temp...@freemail.hu wrote: > > I hesitate to suggest this simple enhancement to the language, because > it's so obvious that *somebody* must have thought of it before. In which > case there must have been a good reason for rejecting it! But here goes: > > *Problem* > The *break* statement jumps out of the nearest enclosing *do, for, > switch, *or *while *statement. All programmers know that breaking out of > a nested for-loop to the *second*-nearest enclosing *do, for, switch, *or > *while *statement is a pain, and requires a *goto* statement or worse. > > *Suggestion* > I suggest the following syntax: > > The *break break* statement jumps out of the second-nearest enclosing *do, > for, switch, *or *while *statement. > The *break break* *break *statement jumps out of the third-nearest > enclosing *do, for, switch, *or *while *statement. > The *break break* *break break *statement jumps out of the > fourth-nearest enclosing *do, for, switch, *or *while *statement. > > And so on. For instance: > > for (int i = 0 ; i < 10 ; i++) > for (int j = 0 ; j < 10 ; j++) > for (int k = 0 ; k < 10 ; k++) { > // do stuff > if (a[i][j][k] == 0) break break break ; // the same as "goto > ContinueExecution ;" > } > ContinueExecution: > > Easy to understand. Easy to implement. 100% backwards compatible. What's > not to like? > > > Serious question: If this is equivalent to 'goto ContinueExecution', then > why not just teach people to use goto? That has the advantage that I don't > have to be careful to figure out where 'break break break;' will go, I can > see the label! > > Chris > It's only equivalent if the label ContinueExecution is actually there. With the goto, you can't be sure where it's actually going to until you actually find that label. That could be up or down any distance within the function. With "break break;", you know exactly where to look. Down to the end of the loop, and then down to the end of the next one. Doesn't seem that hard to me. -- --- 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/?hl=en. ------=_Part_2210_722238.1365360004986 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On Sunday, April 7, 2013 5:06:12 AM UTC-5, Chris Jefferson wrote: =20 =20 =20
On 05/04/13 20:23, temp...@freemail.hu wrote:
I hesitate to suggest this simple enhancement= to the language, because it's so obvious that somebody must have thought of it before. In which case there must have been a good reason for rejecting it! But here goes:

Problem
The break statement jumps out of the nearest enclosing do, for, switch, or while statement. All programmers know that breaking out of a nested for-loop to the second-nearest enclosing do, for, switch, = ;or while statement is a pain, and requires a goto statement or worse.

Suggestion
I suggest the following syntax:

The break break statement jumps out of the second-nearest enclosing do, for, switch, or&nbs= p;while statement.
The break break break statem= ent jumps out of the third-nearest enclosing do, for, switch, or&= nbsp;while statement.
The break break break break = statement jumps out of the fourth-nearest enclosing do, for, switch, = ;or while statement.

And so on. For instance:

for (int i =3D 0 ; i < 10 ; i++)
  for (int j =3D 0 ; j < 10 ; j++)
    for (int k =3D 0 ; k < 10 ; k++) {
      // do stuff
      if (a[i][j][k] =3D=3D 0) break break brea= k ; // the same as "goto ContinueExecution ;"
    }
ContinueExecution:

Easy to understand. Easy to implement. 100% backwards compatible. What's not to like?

Serious question: If this is equivalent to 'goto ContinueExecution', then why not just teach people to use goto? That has the advantage that I don't have to be careful to figure out where 'break break break;' will go, I can see the label!

Chris
 
It's only equivalent if the = label ContinueExecution is actually there.  With the goto, you can't b= e sure where it's actually going to until you actually find that label.&nbs= p; That could be up or down any distance within the function.  With "b= reak break;", you know exactly where to look. Down to the end of the loop, = and then down to the end of the next one.  Doesn't seem that hard to m= e.

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