[Bug c++/68138] "operator== is ambiguous" when comparing a tuple containing values with one containing refs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68138
Patrick Palka changed:
What|Removed |Added
See Also||https://gcc.gnu.org/bugzill
||a/show_bug.cgi?id=93147
CC||ppalka at gcc dot gnu.org
--- Comment #5 from Patrick Palka ---
(In reply to Andrew Pinski from comment #4)
> The original testcase and the one in comment #2 started to work in GCC 11+.
I suspect by r11-2720 aka the fix for PR libstdc++/93147.
(In reply to Harald van Dijk from comment #3)
> Here's a reduced standalone testcase, no libstdc++.
>
> struct Empty { bool operator==(Empty); };
> class tuple_impl : Empty {};
> class tuple : tuple_impl, Empty {};
> bool operator==(tuple, tuple);
> int main() { tuple a, b; a == b; }
>
> tuple derives from Empty twice and would inherit its operator==(Empty)
> member function, except any attempt to use it would be ambiguous. GCC and
> Intel reject this, clang and MSVC accept it using the global
> operator==(tuple, tuple). If tuple only inherits from Empty once, then all
> compilers are in agreement that operator==(tuple, tuple) is a better match
> than the operator==(Empty) member function.
IIUC the ambiguous member lookup makes this example ill-formed, despite the
global operator== otherwise being a better candidate than Empty::operator==.
[Bug c++/68138] "operator== is ambiguous" when comparing a tuple containing values with one containing refs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68138 --- Comment #4 from Andrew Pinski --- The original testcase and the one in comment #2 started to work in GCC 11+.
[Bug c++/68138] "operator== is ambiguous" when comparing a tuple containing values with one containing refs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68138
Harald van Dijk changed:
What|Removed |Added
CC||harald at gigawatt dot nl
--- Comment #3 from Harald van Dijk ---
Here's a reduced standalone testcase, no libstdc++.
struct Empty { bool operator==(Empty); };
class tuple_impl : Empty {};
class tuple : tuple_impl, Empty {};
bool operator==(tuple, tuple);
int main() { tuple a, b; a == b; }
tuple derives from Empty twice and would inherit its operator==(Empty) member
function, except any attempt to use it would be ambiguous. GCC and Intel reject
this, clang and MSVC accept it using the global operator==(tuple, tuple). If
tuple only inherits from Empty once, then all compilers are in agreement that
operator==(tuple, tuple) is a better match than the operator==(Empty) member
function.
[Bug c++/68138] "operator== is ambiguous" when comparing a tuple containing values with one containing refs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68138
Alexander Haase changed:
What|Removed |Added
CC||unsavoryemail at gmail dot com
--- Comment #2 from Alexander Haase ---
Can confirm that this is still an issue up to the latest release of GCC 8.
Here's an even simpler reproduction:
#include
struct Empty {
bool operator == (const Empty &) const { return true; }
};
int main() {
std::tuple a, b;
return a == b;
}
Here's a compiler explorer example where clang and msvc compile the above with
no issue, but gcc does not. Note that clang and gcc use the same stl
implementation as configured for compiler explorer.
https://godbolt.org/z/Em6B9e
[Bug c++/68138] "operator== is ambiguous" when comparing a tuple containing values with one containing refs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68138 --- Comment #1 from Ville Voutilainen --- The test works if operator== is not a member. There's something fairly fishy going on here.
[Bug c++/68138] "operator== is ambiguous" when comparing a tuple containing values with one containing refs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68138 Ville Voutilainen changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2015-11-11 CC||ville.voutilainen at gmail dot com Ever confirmed|0 |1 Known to fail||4.8.2, 4.9.2, 5.2.0, 6.0
