220 3620 <4f808b69-07f9-4bc6-8466-335f77c1989d@isocpp.org> article Path: news.gmane.org!not-for-mail From: Vlad from Moscow Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: "break break ;" etc. to break out of nested loops Date: Sun, 7 Apr 2013 12:47:10 -0700 (PDT) Lines: 196 Approved: news@gmane.org Message-ID: <4f808b69-07f9-4bc6-8466-335f77c1989d@isocpp.org> 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_927_23670915.1365364030402" X-Trace: ger.gmane.org 1365404018 24844 80.91.229.3 (8 Apr 2013 06:53:38 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 8 Apr 2013 06:53:38 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCXLLRHD7IDRBP42Q6FQKGQE5B3GRPY@isocpp.org Mon Apr 08 08:53:39 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-gh0-f197.google.com ([209.85.160.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UP5vj-0007Vd-RN for gclcip-std-proposals@m.gmane.org; Mon, 08 Apr 2013 08:51:52 +0200 Original-Received: by mail-gh0-f197.google.com with SMTP id r17sf7736583ghr.0 for ; Sun, 07 Apr 2013 23:51:50 -0700 (PDT) X-Received: by 10.224.219.146 with SMTP id hu18mr4194132qab.3.1365364031518; Sun, 07 Apr 2013 12:47:11 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.27.137 with SMTP id t9ls2890859qeg.60.gmail; Sun, 07 Apr 2013 12:47:10 -0700 (PDT) X-Received: by 10.49.37.39 with SMTP id v7mr1451801qej.27.1365364030762; Sun, 07 Apr 2013 12:47:10 -0700 (PDT) In-Reply-To: X-Original-Sender: vlad.moscow@mail.ru 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:3620 Archived-At: ------=_Part_927_23670915.1365364030402 Content-Type: text/plain; charset=ISO-8859-1 On Sunday, April 7, 2013 10:40:04 PM UTC+4, Benjamin Lindley wrote: > > 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. > In my opinion break break is even worst then the goto statement. Using break break you should be very cautious counting loops and finding them. If due to refactoring some internal loop will be deleted break break passes the control in the invalid place. If I use the goto statement I will know at least where the control will be passed even if loops will be rearranged.:) So I am against such a proposal. -- --- 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_927_23670915.1365364030402 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
On Sunday, April 7, 2013 10:40:04 PM UTC+4, Benjamin Lindley wrote:On Sunday, April 7, 2013 5:06:12 AM UTC-5, Chris J= efferson 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.
 
 
In my = opinion break break is even worst then the goto statement. Using break= break you should be very cautious counting loops and finding the= m. If due to refactoring some internal loop will be deleted break break pas= ses the control in the invalid place. If I use the goto statement= I will know at least where the control will be passed even if loops w= ill be rearranged.:)
 
So I am against such a prop= osal. 

--
 
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Visit this group at http://groups.google.com/a/isocpp.org/group/std-pro= posals/?hl=3Den.
 
 
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