https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94565
Bug ID: 94565 Summary: C++20: Comparing comparison category types against 0/nullptr is not noexcept Product: gcc Version: 10.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: daniel.kruegler at googlemail dot com Target Milestone: --- The following program should be accepted, but is rejected due to a violation of the static_assertion: Compiler options: -Wall -Wextra -pedantic "-std=c++20" //--------------------- #include <compare> int main() { static_assert(noexcept(std::partial_ordering::less == 0)); } //--------------------- prog.cc: In function 'int main()': prog.cc:5:17: error: static assertion failed 5 | static_assert(noexcept(std::partial_ordering::less == 0)); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The corresponding comparison functions for are all declared as noexcept ([cmp.partialord], [cmp.weakord], [cmp.strongord]), so the clear intention is that such an comparison should be observable as non-throwing operations. The reason why above test fails for all of the existing mixed comparison functions of all the three comparison category types against 0/nullptr is caused by the fact that the implementation-internal type std::__cmp_cat::__unspec in header <compare> misses to declare its converting constructor as noexcept: struct __unspec { constexpr __unspec(__unspec*) { } };