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From: "danakj at orodu dot net" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/110160] New: g++ rejects concept as cyclical with non-matching function signature Date: Wed, 07 Jun 2023 16:55:56 +0000 [thread overview] Message-ID: <bug-110160-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110160 Bug ID: 110160 Summary: g++ rejects concept as cyclical with non-matching function signature Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: danakj at orodu dot net Target Milestone: --- Godbolt: https://godbolt.org/z/d4PhfMqvq Code: ``` #include <sstream> #include <string> template <class T> concept StreamCanReceiveString = requires(T& t, std::string s) { { t << s }; }; struct NotAStream {}; struct UnrelatedType {}; template <StreamCanReceiveString S> S& operator<<(S& s, UnrelatedType) { return s; } static_assert(!StreamCanReceiveString<NotAStream>); static_assert(StreamCanReceiveString<std::stringstream>); ``` What happens here is GCC fails to be able to resolve the expression `StreamCanReceiveString<NotAStream>`. 1. StreamCanReceiveString<NotAStream> tries to do NotAStream << std::string. 2. There is a templated operator<< that takes `StreamCanReceiveString` and `UnrelatedType` 3. Since `UnrelatedType` is not std::string, this is not an overload candidate. 4. Clang and MSVC therefore do not try to recursively solve `StreamCanReceiveString<NotAStream>` and reject the code. But GCC tries to solve the concept and then fails due to recursion.
next reply other threads:[~2023-06-07 16:55 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-06-07 16:55 danakj at orodu dot net [this message] 2023-06-07 17:00 ` [Bug c++/110160] " pinskia at gcc dot gnu.org 2023-06-07 17:37 ` danakj at orodu dot net 2023-06-07 18:25 ` danakj at orodu dot net
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