220 34950 article Path: news.gmane.org!.POSTED!not-for-mail From: Nevin Liber Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Idea about "std::pmr::memory_resource" Date: Sun, 15 Oct 2017 13:06:06 -0500 Lines: 99 Approved: news@gmane.org Message-ID: References: <0a8293b4-3246-47a5-9881-bc1ca4b91772@isocpp.org> <60cbae8d-2a6d-4d1b-9fdf-5c4c913ee0a0@isocpp.org> <97632d14-327a-4af6-8e55-35e753f9557c@isocpp.org> <18b21c5c-ab0f-51ed-1b00-d0cda5c7c046@gmail.com> <5accfbfb-91b3-489e-9e2d-b82149b5ce8e@isocpp.org> <4aa86771-6ade-02fa-b77e-6f0e33f230ac@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="f403045c749cd7b794055b99c005" X-Trace: blaine.gmane.org 1508090808 20992 195.159.176.226 (15 Oct 2017 18:06:48 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 15 Oct 2017 18:06:48 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBCE35H5S6IDBBOGHR3HQKGQEMD3GI3Y@isocpp.org Sun Oct 15 20:06:43 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f197.google.com ([209.85.192.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1e3nJC-0004am-4m for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id k65sor1088849pgc.185.2017.10.15.11.06.47 for (Google Transport Security); Sun, 15 Oct 2017 11:06:47 -0700 (PDT) Received-SPF: pass (google.com: domain of nliber@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.99.112.29 with SMTP id l29mr6201264pgc.2.1508090807038; Sun, 15 Oct 2017 11:06:47 -0700 (PDT) Original-Sender: nliber@gmail.com Original-Received: by 10.100.182.208 with HTTP; Sun, 15 Oct 2017 11:06:06 -0700 (PDT) In-Reply-To: <4aa86771-6ade-02fa-b77e-6f0e33f230ac@gmail.com> X-Original-Sender: nevin@eviloverlord.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=Q1R8+JYE; spf=pass (google.com: domain of nliber@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=nliber@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:34950 Archived-At: --f403045c749cd7b794055b99c005 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, Oct 15, 2017 at 11:27 AM, Jonathan M=C3=BCller < jonathanmueller.dev@gmail.com> wrote: > However, for a hypothetical redesign of the standard library I think this > should be considered. > An allocator interface similar to the simple PMRs as opposed to the > complexity mess that is Allocator, but instead of virtual functions and > class hierarchy it is "concept-based" like Allocator and provides the > possibility of using type erasure. How do you implement a type-erased version of Allocator which can call construct? Please provide a link to working code. Unfortunately, allocators have two jobs: (1) allocate & release memory and (2) construct and destroy objects. They also have a major drawback in that they have to be part of the type system (eg, vector> and vector> are different types). PMRs are about addressing (1) in such a way that using a different allocation scheme does not require a different type family (eg, vector> is the type no matter what allocation scheme is used). If you or the OP has a better way to solve this with the above constraints, present it. If you have different constraints, well, that would be a different proposal and it is a disservice to say that PMRs do not meet that need because PMRs are not trying to meet that need. --=20 Nevin ":-)" Liber +1-847-691-1404 --=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/CAGg_6%2BPQ9w4Yc%3DLHQ8eTCSzha5dakSgeuvp91HA1QUc= 2h-sHxQ%40mail.gmail.com. --f403045c749cd7b794055b99c005 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Sun, Oct 15, 2017 at 11:27 AM, Jonathan M=C3=BCller <jonathanmueller.dev@gmail.com> wrote:
However, for a hypothetical redesign of the standard library I think thi= s should be considered.
An allocator interface similar to the simple PMRs as opposed to the complex= ity mess that is Allocator, but instead of virtual functions and class hier= archy it is "concept-based" like Allocator and provides the possi= bility of using type erasure.

How do you im= plement a type-erased version of Allocator which can call construct?=C2=A0 = Please provide a link to working code.

Unfortunate= ly, allocators have two jobs: =C2=A0(1) allocate & release memory and (= 2) construct and destroy objects.=C2=A0 They also have a major drawback in = that they have to be part of the type system (eg, vector<T, A<T>&g= t; and vector<T, B<T>> are different types).

PMRs are about addressing (1) in such a way that using a different a= llocation scheme does not require a different type family (eg, vector<T,= polymorphic_allocator<T>> is the type no matter what allocation s= cheme is used).

If you or the OP has a better way = to solve this with the above constraints, present it.=C2=A0 If you have dif= ferent constraints, well, that would be a different proposal and it is a di= sservice to say that PMRs do not meet that need because PMRs are not trying= to meet that need.
--
= =C2=A0Nevin ":-)" Liber=C2=A0 <mailto:nevin@eviloverlord.com> =C2=A0+1= -847-691-1404

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