220 12597 <1DB1B82D-0067-4D01-A054-9113B6D7B3ED@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Questions about N3949 - Scoped Resource - Generic RAII Wrapper for the Standard Library Date: Sun, 31 Aug 2014 23:26:44 +0800 Lines: 85 Approved: news@gmane.org Message-ID: <1DB1B82D-0067-4D01-A054-9113B6D7B3ED@gmail.com> References: <038222e0-66c3-4837-b158-e911dffb3c55@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_AC6BF572-F08A-453E-B867-FAB5391CBDE0" X-Trace: ger.gmane.org 1409498823 6599 80.91.229.3 (31 Aug 2014 15:27:03 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 31 Aug 2014 15:27:03 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBO75RSQAKGQEHB4MQTI@isocpp.org Sun Aug 31 17:26:57 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yk0-f198.google.com ([209.85.160.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XO71p-0006r5-PK for gclcip-std-proposals@m.gmane.org; Sun, 31 Aug 2014 17:26:54 +0200 Original-Received: by mail-yk0-f198.google.com with SMTP id q200sf16139523ykb.9 for ; Sun, 31 Aug 2014 08:26:52 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:message-id:mime-version:subject:date :references:to:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=EDuoFXQiUPx+MF70JbJIX/Ldj/JQKNg+EvEdSEuwsA0=; b=PKhv7e2oYTohFxtD6H23/YAsPMmJaRlp3+MwHF9ynkIF0uTSg5++zkOjS3UjaaZdUa vLZILZ9nBDGSuJ1gM6/YUBa7rg2yBZwd6TrwrtRcPaNYrZwyg9mMICPZHexxjZEsaTGf 5k78eVWv436adofyrKuIexaH9x0MXf/Kc4nQCzf++uFCBgYIdNYkdPeRbL6gJ7OPvxOj ZPPXTJucv15i6E1fIIyY6jziIwAXqp1H5WwueLv0k5bk8pbDoaqpTRnyNAiaka3i/6bJ aRI32CPO1DMmzdv+wlW1jSmQK/pXw0gk3/P4RP5vZvrY3PivZfzgWnZirh1F+ekyCMtq bw2Q== X-Gm-Message-State: ALoCoQn/BXTtJMp+Ji9RftdqrUEoyj/s0j5Q1mfYpXKHa3JJK/61TvebRY6kWkBSXSAGTBEifbB+ X-Received: by 10.236.227.169 with SMTP id d39mr10699963yhq.45.1409498812567; Sun, 31 Aug 2014 08:26:52 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.143.76 with SMTP id sc12ls1419199igb.3.gmail; Sun, 31 Aug 2014 08:26:51 -0700 (PDT) X-Received: by 10.70.37.67 with SMTP id w3mr31795887pdj.107.1409498811769; Sun, 31 Aug 2014 08:26:51 -0700 (PDT) Original-Received: from mail-pa0-x22c.google.com (mail-pa0-x22c.google.com [2607:f8b0:400e:c03::22c]) by mx.google.com with ESMTPS id v1si9958547pdq.30.2014.08.31.08.26.51 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 31 Aug 2014 08:26:51 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c03::22c as permitted sender) client-ip=2607:f8b0:400e:c03::22c; Original-Received: by mail-pa0-f44.google.com with SMTP id rd3so10276235pab.31 for ; Sun, 31 Aug 2014 08:26:51 -0700 (PDT) X-Received: by 10.66.124.136 with SMTP id mi8mr32106905pab.89.1409498811358; Sun, 31 Aug 2014 08:26:51 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.53]) by mx.google.com with ESMTPSA id ad10sm19259262pad.4.2014.08.31.08.26.48 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 31 Aug 2014 08:26:50 -0700 (PDT) In-Reply-To: <038222e0-66c3-4837-b158-e911dffb3c55@isocpp.org> X-Mailer: Apple Mail (2.1878.6) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c03::22c as permitted sender) smtp.mail=potswa@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=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:12597 Archived-At: --Apple-Mail=_AC6BF572-F08A-453E-B867-FAB5391CBDE0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=ISO-8859-1 On 2014-08-31, at 10:03 PM, Adi Shavit wrote: > Am I missing something here or is this by design? > What is the rational for this and how would one a succinct scoped_resourc= e declaration? The difference between type-erased shared_ptr and fully-static unique_ptr, = and its cousin scoped_resource, is an indirect function call. This is neces= sary because a shared_ptr can almost never expect to know the dynamic type = of the object it retains, but most unique_ptr use cases statically know the= dynamic type. The solution is to add your own indirect call into the deleter, such as by = using a naked function pointer pointer type as the deleter, or by virtual o= perator (). For what it's worth, I'm not convinced that scoped_resource provides any us= eful encapsulation. Simply writing a class with a destructor is more terse = and more expository. Virtual destructors are among the most widely-known id= ioms in existence, and simply "doing things the old-fashioned way" would li= kely have avoided this deleter confusion entirely. --=20 ---=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. --Apple-Mail=_AC6BF572-F08A-453E-B867-FAB5391CBDE0 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1
On 2014&= ndash;08–31, at 10:03 PM, Adi Shavit <adishavit@gmail.com> wrote:

Am I missin= g something here or is this by design?
What is the rational for t= his and how would one a succinct scoped_resource declaration?

The difference between type-erased shared_ptr and fully-static uni= que_ptr, and its cousin scoped_resource, is an indirect function call. This is necessary because a shared_ptr can almost never expect to know the dynamic type= of the object it retains, but most unique_ptr<= /font> use cases statically know the dynamic type.

The solution is to add your own indirect call into the deleter, such = as by using a naked function pointer pointer type as the deleter, or by virtual operator ().

Fo= r what it’s worth, I’m not convinced that scoped_resource provides any useful encapsulation. Simply writing = a class with a destructor is more terse and more expository. Virtual destru= ctors are among the most widely-known idioms in existence, and simply &ldqu= o;doing things the old-fashioned way” would likely have avoided this = deleter confusion entirely.

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