220 31194 article Path: news.gmane.org!.POSTED!not-for-mail From: Marc Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Domains of specialized `vector` variance Date: Mon, 27 Feb 2017 13:22:02 -0800 (PST) Lines: 73 Approved: news@gmane.org Message-ID: References: <38052307-8ef9-4d41-b902-826f56630c10@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1060_1292457284.1488230522534" X-Trace: blaine.gmane.org 1488230526 6287 195.159.176.226 (27 Feb 2017 21:22:06 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 27 Feb 2017 21:22:06 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCGJRE7HX4IBB65Q2LCQKGQEQIVLOFY@isocpp.org Mon Feb 27 22:22:01 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 1ciSk2-0000rJ-5D for gclcip-std-proposals@m.gmane.org; Mon, 27 Feb 2017 22:21:58 +0100 Original-Received: by mail-qk0-f198.google.com with SMTP id n127sf152246868qkf.3 for ; Mon, 27 Feb 2017 13:22:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to: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=9oIgy7AfqmF1HDLJhgDBOFUpMW64Qdww95mKjVK6pgQ=; b=P/IlSQX8xnqf8l+TypBqQ1GWd9ScEO+dn/EpwdJlNDGnzvh8aFvhHDl21uOFBhZUQ2 4vqwPyin3YJ3ntpKdav+PBF1RFtRhwEoAUFXBJl7KOmE0z08J3jLIG2t3Vtxv/h4f46R 6Jj/cHSpKh+0VUD34fpFvEQ1JEb/MVjFYmqRzbAlJ5/Z2o0xWOsPwqN6jfTy+pKG8bvg xKqYolKskmxvjiHg2MNTeQnWYyT1Bm8IvRR38HmFVdMrDr6Y9iZHbo4Pol49nlZhz1uN 1xZdGI2KKT4gAu5iZDX8o7LroHiaKumMfT84UIyz5mUdDsF95n0WFUDh/yHVv94bCfkD i3RQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to: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=9oIgy7AfqmF1HDLJhgDBOFUpMW64Qdww95mKjVK6pgQ=; b=g6kn7icSRC7Gt8rNp8ntcq0ncpxJ3sx0JCbi3f4fxhqd3C2QZdC9IifACMjHOb6YVd kF+EpsR7XNqfX+gWxRhSk9W1toc/Dsm90PoGFNJXdlXrgesCZ17eGxyHtWvSQSdkuMEe v8yd80ADiasereKKAWIg28uVaYv1BIv+AFBeLdVpABCEnJlrJ5W7tWcPV11yKp8GHJcR JDkBBJx88pJtzBeagYV9oSCRLdWrrvoaChn0MYl+PvNnb1W3Vv3ccRuUJKt3vlLcsA8K WWIdpRTmLW/mu7owbYNYeGp/vTlKOj+0jLbrsLTrLtNLQqAPI9aEJu8UeFgENvNMkaKn Qhng== 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: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=9oIgy7AfqmF1HDLJhgDBOFUpMW64Qdww95mKjVK6pgQ=; b=PpldSCbuFR9k0J7u9qQGfFiIF6Su5olvYZzgQY6q3w1xd4qQkxPw/cAsRont66G/F5 2JXOI/d5g8QBpd014ChdIqinpHk0jNxLGRusQcwLm9XUYZRr3k8HYPk+H8BGfqrwVZq6 ceZFBERG7M2MtrdnjuBXyn4anRqmR/5TlVceF2qPJPwSO2J5xvzBRaU/VbirHyCaTdUL HlXGmg6LS2FAy7ftszxpM/+2iHMbin7jyx52sFEZiItgSyd31+ZME1D7XzlmbBINhJFG oD6RKRnVzXbyfIRA7t7j03CTu8AIKjqV6DE3TWVnyZLC17/Hzsp7gArpGkUzssN+jerT yQ3Q== X-Gm-Message-State: AMke39nzF87G93e2PCLFqQBit02AlNQCQ2DtQBcyAH/IsF9a2DUNrUJzxbKSlHFhqSBXUg== X-Received: by 10.200.53.25 with SMTP id y25mr5082871qtb.45.1488230523981; Mon, 27 Feb 2017 13:22:03 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.21.124 with SMTP id z57ls14934514otz.38.gmail; Mon, 27 Feb 2017 13:22:03 -0800 (PST) X-Received: by 10.157.32.161 with SMTP id x30mr1093037ota.20.1488230523231; Mon, 27 Feb 2017 13:22:03 -0800 (PST) In-Reply-To: <38052307-8ef9-4d41-b902-826f56630c10@isocpp.org> X-Original-Sender: marc.glisse@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:31194 Archived-At: ------=_Part_1060_1292457284.1488230522534 Content-Type: multipart/alternative; boundary="----=_Part_1061_1017512527.1488230522534" ------=_Part_1061_1017512527.1488230522534 Content-Type: text/plain; charset=UTF-8 On Saturday, February 25, 2017 at 6:41:01 PM UTC+1, Nicol Bolas wrote: > What are the other variances that people want? > A variant that I find useful is vector optimized for the empty case: the class contains just one pointer, which is 0 in the empty case, and otherwise points to a buffer that includes both the regular elements of the vector and size/capacity. IIRC mozilla also has a container like that (but limited to POD). I believe that is a valid implementation of std::vector, no functional difference, so it may be hard to specify such a variant... For the variants you propose, whenever I've needed them, using std::vector was close to what I needed (they were local variables so I didn't mind a couple unnecessary pointers), and it might make sense to try and fix those details (in particular let the allocator say how much memory it actually allocated, I think there is already a proposal about it). -- 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/a9defa27-0579-4705-b1e8-075f47619046%40isocpp.org. ------=_Part_1061_1017512527.1488230522534 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Saturday, February 25, 2017 at 6:41:01 PM UTC+1, Nicol = Bolas wrote:
What are the other variances that people want?

A variant that I find useful is vector optimized for the empty case: = the class contains just one pointer, which is 0 in the empty case, and othe= rwise points to a buffer that includes both the regular elements of the vec= tor and size/capacity. IIRC mozilla also has a container like that (but lim= ited to POD). I believe that is a valid implementation of std::vector, no f= unctional difference, so it may be hard to specify such a variant...
For the variants you propose, whenever I've needed them, using std::ve= ctor<T, suitable_allocator> was close to what I needed (they were loc= al variables so I didn't mind a couple unnecessary pointers), and it mi= ght make sense to try and fix those details (in particular let the allocato= r say how much memory it actually allocated, I think there is already a pro= posal about it).

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