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From: "gcc@nicholas-schwab.de" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/98842] optional's spaceship operations generates wrong code when operator== is not present Date: Tue, 26 Jan 2021 18:56:27 +0000 [thread overview] Message-ID: <bug-98842-4-lKcaqhv9nf@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-98842-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98842 gcc@nicholas-schwab.de changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |gcc@nicholas-schwab.de --- Comment #1 from gcc@nicholas-schwab.de --- Three problem lies in the concept three_way_comparable_with. It uses __detail::__weakly_eq_cmp_with that requires u == t. Due to paper P1185 operator== will not lookup operator<=>. Therefore having only operator<=> defined does not suffice to fulfill __detail::__weakly_eq_cmp. Hence the first of these two templates is SFINAE'D out and the second is taken. template<typename _Tp, three_way_comparable_with<_Tp> _Up> constexpr compare_three_way_result_t<_Tp, _Up> operator<=>(const optional<_Tp>& __x, const optional<_Up>& __y) template<typename _Tp, typename _Up> constexpr compare_three_way_result_t<_Tp, _Up> operator<=>(const optional<_Tp>& __x, const _Up& __v) The second will however compare false whenever the left hand side is empty. The standard requires that three_way_comparable_with also requires weakly_equality_comparable. Hence the implementation of this concept is correct. However this might be a defect in the standard. Note that the standard also wants three_way_comparable_with<_Tp> for the second template (http://eel.is/c++draft/optional#comp.with.t-25). So the second template above is non-confirming. But it seems to me that a comparison between two optionals then is always ambiguous, so this should be a defect.
next prev parent reply other threads:[~2021-01-26 18:56 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-01-26 18:09 [Bug libstdc++/98842] New: " nunoplopes at sapo dot pt 2021-01-26 18:56 ` gcc@nicholas-schwab.de [this message] 2021-01-26 21:45 ` [Bug libstdc++/98842] " gcc@nicholas-schwab.de 2021-01-26 22:55 ` redi at gcc dot gnu.org 2021-06-07 14:47 ` cvs-commit at gcc dot gnu.org 2021-06-11 22:25 ` cvs-commit at gcc dot gnu.org 2021-07-22 15:34 ` cvs-commit at gcc dot gnu.org 2021-07-22 15:36 ` redi at gcc dot gnu.org 2024-03-28 11:24 ` redi at gcc dot gnu.org
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