220 28023 <57C48794.6020105@gmail.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Specifier to cause the destructor to be called at last use instead of end of scope Date: Mon, 29 Aug 2016 15:05:56 -0400 Lines: 47 Approved: news@gmane.org Message-ID: <57C48794.6020105@gmail.com> References: <4387866d-169e-44a8-a858-d9aa96d54680@isocpp.org> <85dfd0dc-bf1a-4fa8-81f5-2b36e8f6465c@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: blaine.gmane.org 1472497567 24176 195.159.176.226 (29 Aug 2016 19:06:07 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 29 Aug 2016 19:06:07 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC37LBFWUIFBBFUPSK7AKGQEOZZCUPY@isocpp.org Mon Aug 29 21:06:02 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f198.google.com ([209.85.217.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1beRsc-0005eJ-E2 for gclcip-std-proposals@m.gmane.org; Mon, 29 Aug 2016 21:05:58 +0200 Original-Received: by mail-ua0-f198.google.com with SMTP id m60sf322697781uam.3 for ; Mon, 29 Aug 2016 12:05:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:reply-to:message-id:date:user-agent :mime-version:in-reply-to:x-original-sender :x-original-authentication-results:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=Q3yKxnA3YFgIwFgICluN3dyJVbB48cuWybMZYz7+7xk=; b=EJLWO+itELpZyWkv9I78+CkhtnWMRbzSNqQlO6yVzDiz2wFJK9M4gHJPrWYRJsNxQJ O6NLSVE1b91BXwv2GFYBtoamz0sv3j8/aEFyBaahhhC4a0m4uign3qgwGK8+6wztjWKo hiFlycqBAef3lJ1RfMIkhxDvt7J+ESv+8jkKgYQ7NDRDzEJeM31J+KSF6gUvZr0Qu36o WC+k6wDEKfj5AXAhWJD2iqGhgqiDP2uw9tRgmvtXYh3tXeM289+CcnhaOV55b6TSpOWQ Wg6VdJFOBOpIQX9XmtIFWhu3fUnLFXDz+hUcSLgQOZHTYbQ5my0gE2L+oNz2Fu9//0EJ M9zA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:to:references:from:reply-to:message-id :date:user-agent:mime-version:in-reply-to:x-original-sender :x-original-authentication-results:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=Q3yKxnA3YFgIwFgICluN3dyJVbB48cuWybMZYz7+7xk=; b=X4C2MUuhh4WzHqXzMQ3WRY+7uPXonqPWIjSOEPEpkEeBw5zAXxmxMAuFE7E56hkk6Z NhwCRr5aZRUBhFFY4gdcShDfQU8GbNWBJeZ5rY8pnPvQItdhUl8fDo3p+NgMCxn2E15v NHdNWqk0Ji8TsznBFApodbwOBrUf9NbCR+afrjnyhU+Dl/mV+/hxFbxZord8HgxOhb3s V9aSPwXKEE7DRlPgBrlIQIzdwUA2pQkjUevrz0LTME4adkgm+OvzypqkUGCIEISLgt87 DTrbS1MiZkVP3vuiebpv8namxUaD5YPjGlGOQ5L5ifZMJwjG17SLte8RlXt8H0L5aENU ho5Q== X-Gm-Message-State: AE9vXwP8yJGfEyt1o82jVIPPH7nTvjlX4V7sciH8mObSxtQU184HFas0oxKFpw9dIpomjg== X-Received: by 10.129.82.86 with SMTP id g83mr14569217ywb.14.1472497559091; Mon, 29 Aug 2016 12:05:59 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.24.71 with SMTP id t7ls8778687ott.5.gmail; Mon, 29 Aug 2016 12:05:58 -0700 (PDT) X-Received: by 10.237.44.66 with SMTP id f60mr20634387qtd.11.1472497558181; Mon, 29 Aug 2016 12:05:58 -0700 (PDT) Original-Received: from mail-qt0-x235.google.com (mail-qt0-x235.google.com. 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[66.194.253.20]) by smtp.googlemail.com with ESMTPSA id j67sm19313340qkd.26.2016.08.29.12.05.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Aug 2016 12:05:57 -0700 (PDT) X-Enigmail-Draft-Status: N1110 In-Reply-To: <85dfd0dc-bf1a-4fa8-81f5-2b36e8f6465c@isocpp.org> X-Original-Sender: mwoehlke.floss@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of mwoehlke.floss@gmail.com designates 2607:f8b0:400d:c0d::235 as permitted sender) smtp.mailfrom=mwoehlke.floss@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:28023 Archived-At: On 2016-08-29 14:46, Nicol Bolas wrote: > This problem is fundamentally identical to the temporary lifetime extension > problem. Namely, that this works: > > const auto &str = std::string(...); > //use str > > While this does not: > > const auto &str = std::string(...).c_str(); > //use str I think having explicit temporary types might help here: std::string::c_str() -> char const* register; // declaration // error: taking reference of register-qualified type. const auto &str = std::string(...).c_str(); Obviously, it is too late to change std::string this way, but it would help us write better API's going forward. Specifically: > The compiler does not and *cannot* know, in all cases, whether a > return value of a function contains a pointer/reference to an > argument or an element of an argument. ....it would be a way to solve this. On 2016-08-29 14:52, Nicol Bolas wrote: > So now you want `const virtual register` qualifiers on variables? Do we > *really* need that? Well... *yes*. For exactly the reason given above. Making it a qualifier makes it possible to actually *solve* some of these problems, at least by making them explicitly ill-formed rather than just subtly broken. Mind, this idea isn't fully baked, but it might (*might*) have potential... -- Matthew -- 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/57C48794.6020105%40gmail.com. .