220 34919 article Path: news.gmane.org!.POSTED!not-for-mail From: Ren Industries Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Thoughts on more methods towards containers in the future Date: Sat, 14 Oct 2017 12:44:14 -0400 Lines: 193 Approved: news@gmane.org Message-ID: References: <973f04da-1354-44f4-9d1f-23f04596b8dc@isocpp.org> <20171014085305.GA24512@fukushima.lysator.liu.se> <79c51b8c-6cc2-4872-8651-9dae513d1e21@isocpp.org> <1550fc17-cf97-438d-9e7a-862f729adbf5@isocpp.org> <0cc942cf-a217-4175-98b0-b466ac224dc7@isocpp.org> <7e04a500-ba3a-432a-a844-7d4def1fb739@isocpp.org> <5c1bc3ef-c3a2-4406-8a7a-f82e12155386@isocpp.org> <69a588d5-de2a-4be2-8add-9685d0b9a230@isocpp.org> <405f3ea9-d886-4c3f-9543-a276f8214974@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="089e08221608db5362055b847b2f" X-Trace: blaine.gmane.org 1507999461 1988 195.159.176.226 (14 Oct 2017 16:44:21 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 14 Oct 2017 16:44:21 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDILF3OBTACRBYH5RDHQKGQEFE4U5WQ@isocpp.org Sat Oct 14 18:44:13 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f69.google.com ([74.125.82.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1e3PXl-0007RV-K9 for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id b17sor1659902edj.10.2017.10.14.09.44.15 for (Google Transport Security); Sat, 14 Oct 2017 09:44:15 -0700 (PDT) Received-SPF: pass (google.com: domain of renindustries@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.80.207.12 with SMTP id c12mr6786883edk.106.1507999455333; Sat, 14 Oct 2017 09:44:15 -0700 (PDT) Original-Received: by 10.80.212.13 with HTTP; Sat, 14 Oct 2017 09:44:14 -0700 (PDT) Original-Received: by 10.80.212.13 with HTTP; Sat, 14 Oct 2017 09:44:14 -0700 (PDT) In-Reply-To: <405f3ea9-d886-4c3f-9543-a276f8214974@isocpp.org> X-Original-Sender: RenIndustries@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=OYP+wWjI; spf=pass (google.com: domain of renindustries@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=renindustries@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:34919 Archived-At: --089e08221608db5362055b847b2f Content-Type: text/plain; charset="UTF-8" Do you happen to know of std::array? On Oct 14, 2017 11:40, wrote: > > > On Saturday, October 14, 2017 at 11:26:58 AM UTC-4, Nicol Bolas wrote: >> >> On Saturday, October 14, 2017 at 11:02:29 AM UTC-4, ejsvifq mabmip wrote: >>> >>> The main purpose of C++ containers is to compete with other C style/OOP >>> style implementation. >>> >> >> ... no, it's not. >> >> The main purpose of standard library containers is to be useful to C++ >> programmers. To provide value to the language by having lingua franca types >> that users can use where appropriate for common programming issues. >> >> > No. If vector does not have same performance as T* c style array. > C-style array will just live forever. That is why std::vector is > implemented as templates, not OOP/ > > >> If you add if check for [], that would encourage people continue to use >>> c-style-array for better performance. >>> >>> You have to do everything to make people not have a reason to write >>> their own version of container (for doing the same thing). >>> >> >> No, we don't. The goal of the container design was not to make it so that >> nobody would ever use any other container. It was to make it so that people >> would only use other containers in exceptional circumstances. >> >> There is no one-size-fits-all approach here, and trying to build one will >> only end in tears. >> >> That's not to say that I wouldn't mind having unchecked push-back >> operations on `vector`. I think it's asinine to say that we don't need one >> because optimizers will remove it when they can detect that it will always >> be filled. Optimizers can't see or know everything: >> >> int count; >> file_stream >> count; >> >> vector vec; >> vec.reserve(count); >> >> for(auto x : crange(count)) >> { >> vec.emplace_back(); >> file_stream >> vec.back(); >> } >> >> Can an optimizer remove the test in this case? More importantly, if >> you're looking at this code, is it *reasonable* to expect an optimizer >> to be able to do so? >> >> Pretty hard. > Also we should not expect optimizer to remove test. They have different > behaviors. Before C++11, you might even expect optimizer to optimize copy > for vector. > > -- > 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/405f3ea9-d886-4c3f- > 9543-a276f8214974%40isocpp.org > > . > -- 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/CAMD6iD_5dpmveP_MuK%3DBnYAdbueXC2Z_gRRz38yje_b4m9thZA%40mail.gmail.com. --089e08221608db5362055b847b2f Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Do you happen to know of std::array?

On Oct 14, 2017 11:40, <euloanty@live.com> wrote:


On= Saturday, October 14, 2017 at 11:26:58 AM UTC-4, Nicol Bolas wrote:
On Saturday, October 14, = 2017 at 11:02:29 AM UTC-4, ejsvifq mabmip wrote:
The main purpose of C++ containers is to= compete with other C style/OOP style implementation.

... no, it's not.

The m= ain purpose of standard library containers is to be useful to C++ programme= rs. To provide value to the language by having lingua franca types that use= rs can use where appropriate for common programming issues.
= =C2=A0
No. If vector<T> does not have sa= me performance as T* c style array. C-style array will just live forever. T= hat is why std::vector is implemented as templates, not OOP/
=C2= =A0
If you add if check fo= r [], that would encourage people continue to use c-style-array for better = performance.

You have to do everything to make peo= ple not have a reason to write their own version of container (for doing th= e same thing).

No, we don&#= 39;t. The goal of the container design was not to make it so that nobody wo= uld ever use any other container. It was to make it so that people would on= ly use other containers in exceptional circumstances.

<= div>There is no one-size-fits-all approach here, and trying to build one wi= ll only end in tears.

That's not to say th= at I wouldn't mind having unchecked push-back operations on `vector`. I= think it's asinine to say that we don't need one because optimizer= s will remove it when they can detect that it will always be filled. Optimi= zers can't see or know everything:

int count;
file_stream &= gt;> count;

vector<int> vec;
vec.reserve<= span style=3D"color:#660">(count);

for(auto x : crange<= span style=3D"color:#660">(count))
{
=C2=A0 vec.emplace_= back();=
=C2=A0 file_stream >> vec.back();
}
<= /code>

Can an optimizer remove the test= in this case? More importantly, if you're looking at this code, is it = reasonable to expect an optimizer to be able to do so?

=
Pretty hard.
Also we should not expect op= timizer to remove test. They have different behaviors. Before C++11, you mi= ght even expect optimizer to optimize copy for vector<T>.

--
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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/405f= 3ea9-d886-4c3f-9543-a276f8214974%40isocpp.org.

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