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From: "arthur.j.odwyer at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/102419] [11/12 Regression][concepts] [regression] return-type-requirement of "Y<typename T::type>" does not check that T::type actually exists
Date: Tue, 21 Sep 2021 20:00:34 +0000 [thread overview]
Message-ID: <bug-102419-4-Jvxpplb477@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
--- Comment #4 from Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> ---
> IMHO Clang/MSVC are clearly misbehaving here -- when evaluating the concept-id X<int>, they appear to be substituting {int} into X's constraint-expression instead of into the normal form of X's constraint-expression.
Isn't this situation exactly analogous to `std::void_t`?
template<class T> using void_t = void;
template<class T> auto foo(T t) -> void_t<typename T::type>; // SFINAEs away
template<class T> auto foo(T t) -> int; // this is the only viable candidate
static_assert(std::same_as<decltype(foo(1)), int>);
The language has definitely decided that you can't preemptively fold
`void_t<some-dependent-expression>` down to `void`; I don't think you should be
allowed to preemptively fold `Y<some-dependent-expression>` down to `true`,
either.
I don't know for sure that Clang/MSVC have been authoritatively dubbed
righteous, but their behavior certainly seems, to me, more consistent and
useful than GCC's.
next prev parent reply other threads:[~2021-09-21 20:00 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-20 21:32 [Bug c++/102419] New: [concepts] " 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 [this message]
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 ` [Bug c++/102419] [11/12 Regression][concepts] " jason at gcc dot gnu.org
2022-03-27 19:22 ` 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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