220 35377 <32147114.z48B4pQc9d@tjmaciei-mobl1> article Path: news.gmane.org!.POSTED!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: On P0829 - a freestanding implementation Date: Wed, 15 Nov 2017 18:21:30 -0800 Lines: 68 Approved: news@gmane.org Message-ID: <32147114.z48B4pQc9d@tjmaciei-mobl1> 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 1510798896 28517 195.159.176.226 (16 Nov 2017 02:21:36 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 16 Nov 2017 02:21:36 +0000 (UTC) Cc: Ben Craig To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBLPMWPIAKGQEYGSLT5Y@isocpp.org Thu Nov 16 03:21:31 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 1eF9nz-0006qh-3o for gclcip-std-proposals@m.gmane.org; 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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 Original-Received: from gondolin.macieira.info (gondolin.macieira.info. [78.47.120.188]) by mx.google.com with ESMTP id j25si249601wme.187.2017.11.15.18.21.33 for ; Wed, 15 Nov 2017 18:21:33 -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 B04E411B940; Wed, 15 Nov 2017 18:21:32 -0800 (PST) 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:35377 Archived-At: First of all, let me say that the paper is a a good idea and I support the initiative. I also presented last year[1] at the Embedded Linux Conference Europe on this subject. I had a completely full room of mostly C developers who were interested in learning more. My presentation also had a couple more reasons why (IMNSHO) C++ is better than C, including const correctness and pointer conversions. Second, even though a freestanding implementation is not required to have a heap, most do, of some sort. So even though the paper is correct in saying that all new except the placement one should not be required, I'd like to see a discussion on them being possible. The same goes for exceptions and RTTI: some freestanding uses may want to opt into them, even though they may have a certain amount of overhead. Third, what are the criteria used for this selection? The paper talks about global or thread-specific storage or floating point, which I agree. Some functions appear to be selected for inclusion because they can be reasonably expected to be implemented in exclusively headers, but other ones like memcpy or strpbrk, usually quite complex to implement properly, are included too. Looking at how freestanding C does this, the selection appears to be that freestanding implementations are not required to provide anything that is usually implemented non-inline. Experience of such uses, like the Linux kernel, show that memcpy is expected to NOT exist and be provided by the application (see [2] and [3]). A few specific comments: * why is basic_string_view::compare not required, while memcmp is? It seems really weird to me that a seldom-used function like qsort is required, but very-often-used string comparison isn't. * If the issue with some functions is the use of global state, I'd recommend considering the reentrant portions of , like strtok_r, instead. * The ::at() functions whose only purpose is to throw an exception could simply be modified to not do so and do exactly the same as operator[]. That's for ease of porting of existing code that may use them. * Why are the distributions not included? Because all of them are templates, they MUST be header-only, so why exclude? * The iostreams-using portions (operator<< and operator>>) of should be excluded. * As it stands, std::seed_seq requires use of the heap, so it must be excluded. This needs to be fixed so that non-heap use is possible. See [4]. * I agree on and and would suggest studying giving them non-exception interfaces. I'd be personally interested in that, since Qt could use them if they did not require exceptions. [1] http://events.linuxfoundation.org/sites/events/files/slides/c++embedded.pdf [2] https://code.woboq.org/linux/linux/lib/string.c.html#802 [3] https://code.woboq.org/linux/linux/arch/x86/lib/memcpy_64.S.html#memcpy [4] https://groups.google.com/a/isocpp.org/d/msg/std-discussion/u_yCdZ19Bzo/ SzgMpA5zAAAJ -- 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/32147114.z48B4pQc9d%40tjmaciei-mobl1. .