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From: "hewillk at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/111550] The range adaptor closure object generated by adaptor(args...) is not a perfect forwarding call wrapper Date: Sun, 24 Sep 2023 10:14:51 +0000 [thread overview] Message-ID: <bug-111550-4-qDmjoXTMku@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-111550-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111550 --- Comment #3 from 康桓瑋 <hewillk at gmail dot com> --- Let me report another issue I observed on this PR. According to [range.adaptor.object], adaptor(args...) uses std::forward<decltype((args))>(args).. . to forward arguments into the call wrapper's decayed member, whereas libstdc++ unconditionally uses std::moves, which causes the following code to be rejected: https://godbolt.org/z/EYoxzfWKn #include <ranges> struct NonMovable { NonMovable() = default; NonMovable(const NonMovable&) = default; NonMovable(NonMovable&&) = delete; }; int main() { NonMovable nonmovable; auto r = std::views::take(nonmovable); // hard error in libc++ and lidstdc++ } The libc++ implementation uses std::bind_back, so it will also produce a hard error because std::bind_back requires that the argument must be move-constructible. It seems like only MSVC conforms to the standard's wording. The standard does not require the type of args... here to be move-constructible like other call wrapper factories (such as std::bind_front/std::bind_back/std::bind) do, which seems to introduce some inconsistencies. Although I don't think such constraint is necessary, and I don't know if it's worthy of an LWG?
next prev parent reply other threads:[~2023-09-24 10:14 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-09-23 14:06 [Bug libstdc++/111550] New: " hewillk at gmail dot com 2023-09-24 9:33 ` [Bug libstdc++/111550] " redi at gcc dot gnu.org 2023-09-24 9:39 ` hewillk at gmail dot com 2023-09-24 10:14 ` hewillk at gmail dot com [this message] 2024-01-11 18:16 ` ppalka at gcc dot gnu.org 2024-01-13 4:11 ` ppalka at gcc dot gnu.org
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