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*) { }
};
