220 26132 <6b4ef651-55b3-4b93-a6ac-574b55c7f759@isocpp.org> article Path: news.gmane.org!not-for-mail From: schreiber.corentin@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Allowing unnammed loop variable in range-based for loops? Date: Fri, 3 Jun 2016 03:37:16 -0700 (PDT) Lines: 153 Approved: news@gmane.org Message-ID: <6b4ef651-55b3-4b93-a6ac-574b55c7f759@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_204_1560168322.1464950236858" X-Trace: ger.gmane.org 1464950250 11765 80.91.229.3 (3 Jun 2016 10:37:30 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 3 Jun 2016 10:37:30 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCQLNPVMQILRBXN3YW5AKGQEPDRUW3Q@isocpp.org Fri Jun 03 12:37:26 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f69.google.com ([209.85.214.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1b8mTf-0005xK-Mh for gclcip-std-proposals@m.gmane.org; Fri, 03 Jun 2016 12:37:19 +0200 Original-Received: by mail-it0-f69.google.com with SMTP id i127sf135877580ita.2 for ; Fri, 03 Jun 2016 03:37:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=PqJPhyHos0SvYjkL/EsiI9JCpWOHjASOiEXX/oABUHE=; b=vqxeBFiYrNV3udopOLVr+Sbc3Tc5PQTXxiR76JMUoI6ORRyLIgnx9UUxuVkSfzfRSG Vykxvjgm28jZ1qrSDeRDUI+FekDE57Ki8Re+lbXS3ZieiEWi+sD2nRrVojyV68wVzxeL EUDBjKNAKfBBeFGT+Vbuvdvxiex4R18v/mvpeghaBKNtOnEODn1i6WSmuqwbY8cCwREn 4LccV51KFP9FJIzTz/ArDK2XzSJ1s8ul3r3FpC5qs2Pw4IyyQU6IEUpEo4mDmobQJ7Dr sUv7ow9Gq0e9/wNhCNGGx3l+Ovhptp9fWkbClL5U3oX32fyIjeqebxASoWo8KDAPjDeA bjcg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=PqJPhyHos0SvYjkL/EsiI9JCpWOHjASOiEXX/oABUHE=; b=Jyxg8BoWVMmsyU3jNjxNJiesLOGu+6kWi45gpe2zdY5ohfzwRU8RORSaQ6KaqqOQxp eialwRTABMTl3du5vVaqtG63Z3LL+trRGthNc4i6cKW3WrbYnGuBtHTPaXeI1PBhiO/Y dmpJ+6CxzJ/0VaanARm5Be/B5uMQBzY21sAAsbRTrD9IKV7P7szSUzHCZAvtOk2R5x5U XIBNhMDEKYZJioWCO652kzYteqJrxy9hYXa0UhjYRoRTqfNCnsd7so2uUZN38g6jsOZ3 r1inCaP9xHhgVjoyz5U8MMN39XJzjUI2X5fjSBn/TO/FjjcKBz/rYC7Z1vvO6uJ0+f5s eWiw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=PqJPhyHos0SvYjkL/EsiI9JCpWOHjASOiEXX/oABUHE=; b=MwNaslUNkntlGelVuD3cP/B6Vcpvir220ADVZKUcKcU6NKMsAiWqfXGNq34OQJlAWY koiKhwYI9/JvGmPG/ZZSkZSRi9eVEo/BNmFim5aLc6WHu+e9ztMjn6KK9vrv0EyH/hGX R0QrbA0/9psd1SHKECwR+lit6WsMe94aIMZUXiKG998nCbb8ZUl3DmRz5JvrCIJXvOBi XGA7/qg/BOgmoCEdtXAjw0UyZZp/pGZATW91aSGGEYpQSSOutKCtO138SCmZP9O+Bmz8 JOjaTQDMpBmog6eTALKsJbLauRI3kGtQ0rDhfCgLtxpHMPdI/+gPFUIMVLW86PJwCVH8 iphw== X-Gm-Message-State: ALyK8tJatn2slhWEfrBgolmN9XLHAx6G22xzIK0RBxFVTFsiFGxsoH0sa+baHiLjQGpCUw== X-Received: by 10.36.43.69 with SMTP id h66mr2596183ita.10.1464950238255; Fri, 03 Jun 2016 03:37:18 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.150.195 with SMTP id z186ls336800itd.40.gmail; Fri, 03 Jun 2016 03:37:17 -0700 (PDT) X-Received: by 10.36.213.134 with SMTP id a128mr77114itg.8.1464950237551; Fri, 03 Jun 2016 03:37:17 -0700 (PDT) X-Original-Sender: schreiber.corentin@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:26132 Archived-At: ------=_Part_204_1560168322.1464950236858 Content-Type: multipart/alternative; boundary="----=_Part_205_291784764.1464950236859" ------=_Part_205_291784764.1464950236859 Content-Type: text/plain; charset=UTF-8 I have defined a utility function "range(n)" that generates a input sequence of integers from 0 to n-1 such that for (int i : range(10)) { // ... } // Is equivalent to for (int i = 0; i < 10; ++i) { // ... } I think a similar utility is present in the range TS, although I do not know it exact name. I recently encountered a situation when I needed to perform "n" iterations, but without caring about "which" iteration is currently being performed; I didn't use the value of "i" in the example above. The problem is, compilers start warning on unused variable... See running code here: http://cpp.sh/9lot Obviously there are various ways around this, in particular using the traditional for loop does not generate a warning. But range-based for loops are superior in many ways, and it would be good to be able to use it in this situation. I also think the warning is correct, since there is no way for the compiler to know your intention here (maybe you just made a typo and intended to use "i"?). Therefore, do you think it would be possible to solve this issue by allowing the range variable to be unnamed? Something like: for (int : range(10)) { // ... } That would also make one's intention clearer. -- 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/6b4ef651-55b3-4b93-a6ac-574b55c7f759%40isocpp.org. ------=_Part_205_291784764.1464950236859 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
I have defined a utility function "range(n)" tha= t generates a input sequence of integers from 0 to n-1 such that
for (int i : range(10)) {
=C2=A0 =C2=A0 // ...
}

// Is equivalent to

for (int i =3D 0; i < 10; <= /span>++i) {
=C2=A0 =C2=A0 // ...
}

I think a similar utility is pre= sent in the range TS, although I do not know it exact name.

I recent= ly encountered a situation when I needed to perform "n" iteration= s, but without caring about "which" iteration is currently being = performed; I didn't use the value of "i" in the example above= .. The problem is, compilers start warning on unused variable... See running= code here: http://cpp.sh/9lot

Obviously there are various ways arou= nd this, in particular using the traditional for loop does not generate a w= arning. But range-based for loops are superior in many ways, and it would b= e good to be able to use it in this situation. I also think the warning is = correct, since there is no way for the compiler to know your intention here= (maybe you just made a typo and intended to use "i"?). Therefore= , do you think it would be possible to solve this issue by allowing the ran= ge variable to be unnamed? Something like:

for (int := range(10)) {
=C2=A0 =C2=A0 // ...
}

That would also make one's i= ntention clearer.

--
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