220 33183 article Path: news.gmane.org!.POSTED!not-for-mail From: Dan Raviv Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: [idea for proposal] Adding std::shift to Date: Wed, 12 Jul 2017 16:56:11 +0300 Lines: 232 Approved: news@gmane.org Message-ID: References: <55df161b-f0c5-4d81-ad1d-882425e7bf8a@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="001a11408742f5858105541f2e72" X-Trace: blaine.gmane.org 1499867809 27484 195.159.176.226 (12 Jul 2017 13:56:49 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 12 Jul 2017 13:56:49 +0000 (UTC) Cc: "dan@soundradix.com" To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC5YJREBWAGRBEGVTDFQKGQE6GEPOMA@isocpp.org Wed Jul 12 15:56:40 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f198.google.com ([209.85.220.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dVI7w-0006AS-Bl for gclcip-std-proposals@m.gmane.org; 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[2607:f8b0:4003:c06::229]) by mx.google.com with ESMTPS id c141si1749927oig.176.2017.07.12.06.56.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 12 Jul 2017 06:56:32 -0700 (PDT) Received-SPF: pass (google.com: domain of dan.raviv@gmail.com designates 2607:f8b0:4003:c06::229 as permitted sender) client-ip=2607:f8b0:4003:c06::229; Original-Received: by mail-oi0-x229.google.com with SMTP id l130so20089430oib.1 for ; Wed, 12 Jul 2017 06:56:32 -0700 (PDT) X-Received: by 10.202.231.143 with SMTP id e137mr3598068oih.189.1499867792112; Wed, 12 Jul 2017 06:56:32 -0700 (PDT) Original-Received: by 10.74.71.207 with HTTP; Wed, 12 Jul 2017 06:56:11 -0700 (PDT) In-Reply-To: <55df161b-f0c5-4d81-ad1d-882425e7bf8a@isocpp.org> X-Original-Sender: dan.raviv@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.b=G3rETkMS; spf=pass (google.com: domain of dan.raviv@gmail.com designates 2607:f8b0:4003:c06::229 as permitted sender) smtp.mailfrom=dan.raviv@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-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:33183 Archived-At: --001a11408742f5858105541f2e72 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sure, it can return an iterator (or at least have an overload which does) similar to std::rotate / std::move. I agree about constexpr, but I guess that would come with the rest of the algorithms become constexpr. Since it's such a simple algorithm, with the main benefit of adding it to the STL being adding readability/efficiency/concise, I'm not whether submitting it to boost.algorithm first would be a more effective way to go than just making a proposal. What do you think? Thanks, Dan On Wed, Jul 12, 2017 at 2:18 PM, Alexander Zaitsev wrote: > Hello. > > Really nice idea! But i have some suggestions: > * shift should return iterator (or two) > * it should be constexpr > > Also i suggest you create PR to Boost.Algorithm (or we can work together = - > i will help you as mush as possible). And after including into > Bost.Algorithm we can write proposal to C++ Standard. > > =D1=81=D1=80=D0=B5=D0=B4=D0=B0, 12 =D0=B8=D1=8E=D0=BB=D1=8F 2017 =D0=B3.,= 12:53:19 UTC+3 =D0=BF=D0=BE=D0=BB=D1=8C=D0=B7=D0=BE=D0=B2=D0=B0=D1=82=D0= =B5=D0=BB=D1=8C d...@soundradix.com > =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB: >> >> Hi, >> >> Would anyone be interested in adding std::shift to ? >> >> It would be similar to both: >> - std::rotate, but without moving the head elements back to the tail. >> This would allow a more efficient implementation and clearer semantics i= n >> case rotation is not needed as well as correctness in case rotation is >> undesired. >> - 's std::move/std::move_backward (depending on the shift >> direction). >> >> std::shift should probably accommodate both left and right shifts by one >> of: >> - giving it either begin() and end(), or rbegin() and rend(), similar to >> how std::rotate works for both left and right rotations. The advantage i= s >> compactness of the implementation. >> - allowing the shift count parameter to be either positive or negative. >> The advantage is compactness, though it might not be clear which directi= on >> is which - to be consistent with rotate, positive integers should shift = to >> the left. >> - having std::shift_right and std::shift_left functions. The advantage i= s >> clarity when calling the methods, although the same argument could be ma= de >> for having separate std::rotate_left and std::rotate_right instead of >> std::rotate, which we don't have. >> >> Here's a sample implementation of a shift to the right direction: >> >> template >> void shift_right(BidirIt first, BidirIt last, unsigned int n =3D 1) >> { >> std::move_backward(first, last - n, last); >> } >> >> This demonstrates that while std::shift is implementable with >> std::move/std::move_backward, >> 1) It isn't immediately clear from the code (at least to my eyes) that >> this is a shift right, unless you are intimately familiar with >> std::move_backward. >> 2) Different calls, either to std::move or to std::move_backward, are >> required, depending on the shift direction. >> >> So, implementing std::shift would allow writing more readable code. >> >> Thanks, >> Dan >> > -- > 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/55df161b-f0c5-4d81- > ad1d-882425e7bf8a%40isocpp.org > > . > --=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/CADw4SdSinGPK9rYUm4LHW-f%3DA3fW6R3si%2BLu%2BAqoJ= %3DbQNBMvTQ%40mail.gmail.com. --001a11408742f5858105541f2e72 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Sure, it can return an iterator (or at least have an overl= oad which does) similar to std::rotate / std::move.
I agree about const= expr, but I guess that would come with the rest of the <algorithm> al= gorithms become constexpr.

Since it's such a s= imple algorithm, with the main benefit of adding it to the STL being adding= readability/efficiency/concise, I'm not whether submitting it to = boost.algorithm first would be a more effective way to go than just making = a proposal. What do you think?

Thanks,
D= an

On = Wed, Jul 12, 2017 at 2:18 PM, Alexander Zaitsev <zamazan4ik@gmail.com> wrote:
Hel= lo.

Really nice idea! But i have some suggestions:
=
* shift should return iterator (or two)
* it should be const= expr

Also i suggest you create PR to Boost.Algorit= hm (or we can work together - i will help you as mush as possible). And aft= er including into Bost.Algorithm we can write proposal to C++ Standard.
=
=D1=81=D1=80=D0=B5=D0=B4=D0=B0, 12 =D0=B8=D1=8E=D0=BB=D1=8F 2017 =D0=B3= .., 12:53:19 UTC+3 =D0=BF=D0=BE=D0=BB=D1=8C=D0=B7=D0=BE=D0=B2=D0=B0=D1=82=D0= =B5=D0=BB=D1=8C d.= ...@soundradix.com =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB:
Hi,
Would anyone be interested in adding std::shift to <algorith= m>?=C2=A0

It would be similar to both:
- std::rotate, but without moving the head elements back to the tail. Thi= s would allow a more efficient implementation and clearer semantics in case= rotation is not needed as well as correctness in case rotation is undesire= d.
- <algorithm>'s std::move/std::move_backward (depend= ing on the shift direction).

std::shift should pro= bably accommodate both left and right shifts by one of:
- giving = it either begin() and end(), or rbegin() and rend(), similar to how std::ro= tate works for both left and right rotations. The advantage is compactness = of the implementation.
- allowing the shift count parameter to be= either positive or negative. The advantage is compactness, though it might= not be clear which direction is which - to be consistent with rotate, posi= tive integers should shift to the left.
- having std::sh= ift_right and std::shift_left functions. The advantage is clarity when call= ing the methods, although the same argument could be made for having separa= te std::rotate_left and std::rotate_right instead of std::rotate, which we = don't have.

Here's a sample implemen= tation of a shift to the right direction:

template<class BidirIt>
void shift_right(BidirIt<= span style=3D"color:#000"> first,<= span style=3D"color:#000"> BidirIt= last, unsigned int n =3D 1)
{
=C2=A0 =C2=A0 std::move_backward(first= , last<= /span> - n, last);
}
<= /code>

This demonstrates that while std::shift is = implementable with std::move/std::move_backward,
1) It isn't = immediately clear from the code (at least to my eyes) that this is a shift = right, unless you are intimately familiar with std::move_backward.
2) Different calls, either to std::move or to std::move_backward, are req= uired, depending on the shift direction.

So, imple= menting std::shift would allow writing more readable code.

Thanks,
Dan
<= span class=3D"">

--
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