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From: "rudick at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/102804] New: template matching fails w/ false ambiguity on
 ternary expressions with enums
Date: Sun, 17 Oct 2021 22:09:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102804

            Bug ID: 102804
           Summary: template matching fails w/ false ambiguity on ternary
                    expressions with enums
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rudick at gmail dot com
  Target Milestone: ---

E.g. w/ -std=3Dc++11

#include <iostream>
int main() {
  enum: unsigned int32_t { FOO, BAR } foobar =3D FOO;
  std::cout << ((time(nullptr) % 2) ? foobar : 13) << std::endl;
}

The initial error is:

error: ambiguous overload for =E2=80=98operator<<=E2=80=99 (operand types a=
re =E2=80=98std::ostream=E2=80=99
{aka =E2=80=98std::basic_ostream<char>=E2=80=99} and =E2=80=98unsigned int=
=E2=80=99)

in gcc9.2 & gcc 11.2.0

gcc7 happily compiles the code.

with -Wextra, all 3 versions warn:

error: enumerated and non-enumerated type in conditional expression

Version: 11.2.0

system: CentOS Linux 7.7.1908 on Intel Xeon

command: g++ -Wall -Wextra -std=3Dc++11 20211017-bug.cpp=