From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 123286 invoked by alias); 19 Mar 2018 12:21:34 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 123209 invoked by uid 89); 19 Mar 2018 12:21:26 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.7 required=5.0 tests=AWL,BAYES_00,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 spammy= X-HELO: mx1.redhat.com Received: from mx3-rdu2.redhat.com (HELO mx1.redhat.com) (66.187.233.73) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 19 Mar 2018 12:21:24 +0000 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5A745406802D; Mon, 19 Mar 2018 12:21:23 +0000 (UTC) Received: from [127.0.0.1] (ovpn04.gateway.prod.ext.ams2.redhat.com [10.39.146.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id C783A202322C; Mon, 19 Mar 2018 12:21:22 +0000 (UTC) Subject: Re: [PATCH 2/2] Add gdb::string_view To: Simon Marchi , gdb-patches@sourceware.org References: <20180317234902.18278-1-simon.marchi@polymtl.ca> <20180317234902.18278-2-simon.marchi@polymtl.ca> <2d68023c-7f24-7eb5-2822-00815b41ba2a@polymtl.ca> From: Pedro Alves Message-ID: <8a3ae923-adad-82a4-67bb-8c303511c010@redhat.com> Date: Mon, 19 Mar 2018 12:21:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <2d68023c-7f24-7eb5-2822-00815b41ba2a@polymtl.ca> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SW-Source: 2018-03/txt/msg00351.txt.bz2 On 03/18/2018 12:10 AM, Simon Marchi wrote: > On 2018-03-17 19:49, Simon Marchi wrote: >> We had a few times the need for a data structure that does essentially >> what C++17's std::string_view does, which is to give an std::string-like >> interface (only the read-only operations) to an arbitrary character >> buffer. Great, I've been wanting to do something like this for a while. >> >> I first copied the string_view file from today's gcc master >> (b427286632d7) and adapted it (I don't think there should be any legal >> issues since the copyright should already belong to the FSF): >> >> - I removed things related to wstring_view, u16string_view and >> u32string_view (I don't think we need them, but we can always add them >> later). >> - I removed usages of _GLIBCXX_BEGIN_NAMESPACE_VERSION and >> _GLIBCXX_END_NAMESPACE_VERSION. >> - I put the code in the gdb namespace. I had to add a few "std::" in front of >> std type usages. >> - I added a constructor that builds a string_view from an std::string, >> so that we can pass strings to string_view parameters seamlessly. >> Normally, that's handled by "operator __sv_type" in the std::string >> declaration, but it only exists when building with c++17. >> - When building with >= c++17, gdb::string_view is an alias of >> std::string_view. >> >> The result is close enough to the original file that if we ever need to >> update it, it should be easy enough to compare it with the new version >> in a diff editor and merge the new changes in. > > Hmm, when building with older g++ (such as the aarch64 builders on the buildbot, > which have g++ 4.8), it trips on: > > using __idt = std::common_type_t<_Tp>; > > It looks like that release of g++ didn't have std::common_type_t. I guess it > would be possible to avoid using it, and change these: It has std::common_type though. C++14 std::foo_t types are usually just a helper/convenience alias template, like: /// Alias template for common_type template using common_type_t = typename common_type<_Tp...>::type; So it sounds like we can just use the C++11 / ::type form directly, or add gdb::common_type_t somewhere, like common/traits.h or to our copy of string_view. > > operator==(basic_string_view<_CharT, _Traits> __x, > __detail::__idt> __y) noexcept > > for > > operator==(basic_string_view<_CharT, _Traits> __x, > basic_string_view<_CharT, _Traits> __y) noexcept > > but I am not aware of what consequences it would have. Would it be possible to import some of the libstdc++'s relevant testscases into our unit tests framework, like was done for gdb::optional [1]? [1] https://sourceware.org/ml/gdb-patches/2017-04/msg00239.html Thanks, Pedro Alves