220 34912 <02fc9853-e388-4eb3-8db3-de4e0a689056@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: euloanty@live.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Thoughts on more methods towards containers in the future Date: Sat, 14 Oct 2017 08:44:42 -0700 (PDT) Lines: 190 Approved: news@gmane.org Message-ID: <02fc9853-e388-4eb3-8db3-de4e0a689056@isocpp.org> 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/mixed; boundary="----=_Part_14344_1664848131.1507995882416" X-Trace: blaine.gmane.org 1507995881 17991 195.159.176.226 (14 Oct 2017 15:44:41 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 14 Oct 2017 15:44:41 +0000 (UTC) Cc: euloanty@live.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDPYX6PYRQNBB27BRDHQKGQEFD4M5AQ@isocpp.org Sat Oct 14 17:44:37 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f71.google.com ([209.85.213.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1e3Oc8-00045Q-LV for gclcip-std-proposals@m.gmane.org; Sat, 14 Oct 2017 17:44:36 +0200 Original-Received: by mail-vk0-f71.google.com with SMTP id b5sf4452878vkf.3 for ; Sat, 14 Oct 2017 08:44:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=Oylm6KLhP97VX0ZruBB1jbGP8KNzZ9GA5CQUfOIDOZs=; b=lVgUhQHniFi3ugJzRSsHxeMzHxfdt6sdPkBGFUAq4MKsvQvzj8hISgOZWR8cYN5l3s ttEnO2JWlsAPrxcG/NyVGD7NsF4HpSpj2WMcEN/L1u619XR8kPtLN+sft1eIoWHWcbO9 6uKT9FR70FNvKwXFUQRqTlMQCO2wSeQ/YbB+rUBrCLmpYFU8kVv6dn505xhs6ot9O+0R xOY1I+D+o0+XSjbLp9mgD83xnbJLGmPS71KBFRUlyPSAhjeI3ckIf6YuLbM7nTZb1mj7 FQ0HKWNIqyOc2QvaAo1d/1Pi9fALCu3+aDG61CLBkyTdcmdY916tIazNqzRGHka+JlZ/ 8i9g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references: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=Oylm6KLhP97VX0ZruBB1jbGP8KNzZ9GA5CQUfOIDOZs=; b=aGmmYmGDUOGogr5MZAmjD3wqH/ullUSeirSNZoXA91TeqhTAMxaJu7GmPu+bl3fTP8 pXoFPF6s6HMcW5tX3FSTI8hzcb2gHBGOpP8iXPvLQD4giV1rQR3qnoMi/zc3YNz3578J GIxoDvWyxlyY6VyOrSJEIQnuQYLrJbiqSPON+v7lR5HoxCOQnO6+cE5CaBs5PTXYP2TZ 7JWtjX1Ihg1DM8/MOyDJbmDZH5RJQFyDQN8vPrDOsFIC0JcAS9K5sNNuWpJYDfCi19Ty ajlEq61i3PLFGkj6USTONem4Rm8poxUitWxeyW4XHvNX+FkYEsDbJVR4cRVe7gOq8Q8r MqFA== X-Gm-Message-State: AMCzsaXEXebwSXdfcf29O6c8EzzUU15d7nB8E+PiJRqJPiebQl4jeY97 4FiAhurKu/wVRk3ny+AwPmyHaQ== X-Google-Smtp-Source: AOwi7QDmhB1iu79y4TyxXDMEfYc49LLx4U503TyKVRqLZsxJZQbkGsOpWlXtJLRB8EmjU/+yxJpYAQ== X-Received: by 10.176.82.184 with SMTP id v53mr2483573uav.84.1507995884023; Sat, 14 Oct 2017 08:44:44 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.138.69 with SMTP id m66ls2409490vkd.15.gmail; Sat, 14 Oct 2017 08:44:42 -0700 (PDT) X-Received: by 10.31.161.87 with SMTP id k84mr308601vke.7.1507995882867; Sat, 14 Oct 2017 08:44:42 -0700 (PDT) In-Reply-To: <405f3ea9-d886-4c3f-9543-a276f8214974@isocpp.org> X-Original-Sender: euloanty@live.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:34912 Archived-At: ------=_Part_14344_1664848131.1507995882416 Content-Type: multipart/alternative; boundary="----=_Part_14345_922031132.1507995882417" ------=_Part_14345_922031132.1507995882417 Content-Type: text/plain; charset="UTF-8" For example. I want to test whether I reserve the exactly correct capacity for vector. vector v; v.reserve(100000); //emplace_back for 100001 times. I cant find mistakes. vector v; v.reserve(100000); //non check emplace_back for 100001 times This program will collapse. And I can know I've made mistake here. On Saturday, October 14, 2017 at 11:40:03 AM UTC-4, eulo...@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 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/02fc9853-e388-4eb3-8db3-de4e0a689056%40isocpp.org. ------=_Part_14345_922031132.1507995882417 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
For example. I want to test whether I reserve the exa= ctly correct capacity for vector.


v= ector<int> v;
v.reserve(100000);
//emplace_back f= or=C2=A0100001 times. I cant find mistakes.


vector<int> v;
v.reserve(100000);
//non check emplace_back for=C2=A0100001 times
This progra= m will collapse. And I can know I've made mistake here.

On Saturday, October 14, 2017 at 11:40:03 AM UTC-4, eulo...@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 i= s to compete with other C style/OOP style implementation.

... no, it's not.

T= he main purpose of standard library containers is to be useful to C++ progr= ammers. To provide value to the language by having lingua franca types that= users can use where appropriate for common programming issues.
=C2=A0
No. If vector<T> 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/
= =C2=A0
If you add if check= for [], that would encourage people continue to use c-style-array for bett= er 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 do= n'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 optimi= zers will remove it when they can detect that it will always be filled. Opt= imizers can't see or know everything:

int= count;=
file_stream >> count;

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

for(<= span style=3D"color:#008">auto x <= span style=3D"color:#660">: crange= (count<= span style=3D"color:#660">))
{
=C2=A0 vec<= /span>.emplace= _back();
=C2=A0 file_stream >> vec.back();
}
=

Can an optimizer remove the tes= t 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 o= ptimizer to remove test. They have different behaviors. Before C++11, you m= ight even expect optimizer to optimize copy for vector<T>.

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/02fc9853-e388-4eb3-8db3-de4e0a689056= %40isocpp.org.
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