220 35405 <1747398.ysixVUWvEu@tjmaciei-mobl1> article Path: news.gmane.org!.POSTED!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: On P0829 - a freestanding implementation Date: Sun, 19 Nov 2017 11:16:34 -0800 Lines: 39 Approved: news@gmane.org Message-ID: <1747398.ysixVUWvEu@tjmaciei-mobl1> References: <32147114.z48B4pQc9d@tjmaciei-mobl1> <9215639.TL3RHUUBQ5@tjmaciei-mobl1> <25d0417e-8fa0-47ee-a70b-3ce7b10c1fee@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 1511118997 29530 195.159.176.226 (19 Nov 2017 19:16:37 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 19 Nov 2017 19:16:37 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBFFRY7IAKGQEVL2OVMQ@isocpp.org Sun Nov 19 20:16:31 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wr0-f198.google.com ([209.85.128.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eGV4w-0007Gf-Gr for gclcip-std-proposals@m.gmane.org; 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[78.47.120.188]) by mx.google.com with ESMTP id v203si6348722wmv.252.2017.11.19.11.16.36 for ; Sun, 19 Nov 2017 11:16:36 -0800 (PST) Received-SPF: pass (google.com: domain of thiago@macieira.org designates 78.47.120.188 as permitted sender) client-ip=78.47.120.188; Original-Received: from tjmaciei-mobl1.localnet (unknown [IPv6:2601:1c0:4501:5f9f:e0ee:4594:419f:8f32]) by gondolin.macieira.info (Postfix) with ESMTPSA id DA5BF11B99E for ; Sun, 19 Nov 2017 11:16:35 -0800 (PST) In-Reply-To: <25d0417e-8fa0-47ee-a70b-3ce7b10c1fee@isocpp.org> X-Original-Sender: thiago@macieira.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of thiago@macieira.org designates 78.47.120.188 as permitted sender) smtp.mailfrom=thiago@macieira.org 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:35405 Archived-At: On sexta-feira, 17 de novembro de 2017 20:25:44 PST Nicol Bolas wrote: > On Friday, November 17, 2017 at 6:39:33 PM UTC-5, Thiago Macieira wrote: > > typeid() must return a reference to an object whose address can be > > compared > > across translation units. > > Is that really something we need to require from implementations? Isn't > having them compare equal good enough? And I'm not just talking about > freestanding here. You're right, comparing pointer addresses is not a guarantee. There needs to be a way to compare them and std::type_info does have operator==. How that's implemented is ABI-specific. Both libstdc++ (libsupc++) and libc++ (libc++abi) do a pointer comparison of the typeinfo name but also have a fallback to doing a string comparison. The #define that disables that string comparison appears not to be used (anymore), probably shown by this comment in libstdc++'s : // We used to do inline pointer comparison by default if weak symbols // are available, but even with weak symbols sometimes names are not merged // when objects are loaded with RTLD_LOCAL, so now we always use strcmp by // default. So, in fact, in a freestanding implementation, this could be allowed again, since there would be no dynamic module loading. There would still be a minor ABI change to emit the TI objects for primitives, but that's something easily within reach of the compiler developers. -- Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Software Architect - Intel Open Source Technology Center -- 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/1747398.ysixVUWvEu%40tjmaciei-mobl1. .