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From: "jason at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/102419] [11/12 Regression][concepts] return-type-requirement of "Y<typename T::type>" does not check that T::type actually exists Date: Sun, 27 Mar 2022 19:21:27 +0000 [thread overview] Message-ID: <bug-102419-4-VkCAW0WLlO@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-102419-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102419 Jason Merrill <jason at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jason at gcc dot gnu.org Summary|[11/12 |[11/12 |Regression][concepts] |Regression][concepts] |[regression] |return-type-requirement of |return-type-requirement of |"Y<typename T::type>" does |"Y<typename T::type>" does |not check that T::type |not check that T::type |actually exists |actually exists | --- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> --- Concept satisfaction was very deliberately designed in committee discussion to work differently from void_t, based on the normalized form rather than the concept-id as written. So this example is well-formed: template <class Tz> concept is_void = same_as(Tz, void); template <class Ta, class Tb> concept void_or_same = is_void<Ta> || same_as<Ta, Tb>; template <class T> void f() requires void_or_same<T,T&>; int main() { f<void>(); } // OK It definitely is an inconsistency with non-concept template-ids, but that's the design. C++20 national body comment CA104 (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p2103r0.html#CA104) is about one situation where we do need to substitute directly into the arguments, but it is a single exception to the rule. In the discussion of CA104 I suggested that we might want to reconsider this design (on 2019-11-08, if you want to look up the reflector message), and make my example above ill-formed, but we ended up making an exception instead. The behavior change you are seeing is from properly implementing http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1452r2.html and not a bug.
next prev parent reply other threads:[~2022-03-27 19:21 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-09-20 21:32 [Bug c++/102419] New: [concepts] [regression] " arthur.j.odwyer at gmail dot com 2021-09-21 6:46 ` [Bug c++/102419] [11/12 Regression][concepts] " rguenth at gcc dot gnu.org 2021-09-21 14:49 ` ppalka at gcc dot gnu.org 2021-09-21 14:56 ` ppalka at gcc dot gnu.org 2021-09-21 15:18 ` ppalka at gcc dot gnu.org 2021-09-21 20:00 ` arthur.j.odwyer at gmail dot com 2021-09-23 14:58 ` ppalka at gcc dot gnu.org 2022-01-17 13:29 ` rguenth at gcc dot gnu.org 2022-03-27 19:21 ` jason at gcc dot gnu.org [this message] 2022-03-27 19:22 ` [Bug c++/102419] [11/12 Regression][concepts] " jason at gcc dot gnu.org 2022-04-21 7:50 ` rguenth at gcc dot gnu.org 2023-03-30 17:08 ` [Bug c++/102419] [11/12/13 " ppalka at gcc dot gnu.org 2023-05-29 10:05 ` [Bug c++/102419] [11/12/13/14 " jakub at gcc dot gnu.org 2023-11-28 20:44 ` ppalka at gcc dot gnu.org
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