https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118029
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
For extra fun:
enum E { E0, E1, E2 };
E operator|(E lhs, E rhs) { return E(int(lhs) | int(rhs)); }
void f(E e)
{
e |= E1|E2;
}
e2.cc: In function 'void f(E)':
e2.cc:6:11: error: invalid conversion from 'int' to 'E' [-fpermissive]
6 | e |= E1|E2;
| ^~
| |
| int
Now this seems really bad. If the user understands that a |= b works like a =
a|b then it's really confusing where the int comes from, because a|b isn't an
int.
So they have to know that it's a bit like a=a|b but not really.
Again, EDG is great:
"e2.cc", line 6: error: this operation on an enumerated type requires an
applicable user-defined operator function
e |= E1|E2;
^
1 error detected in the compilation of "e2.cc".
This clearly states that the built-in |= will never work, it doesn't matter
what the type of the right operand is.
EDG gives this diagnostic for all compound assignments that don't have a
user-defined overload. G++ only seems to be confusing for the bitwise compound
assignments &= and |= and ^=
For += on enums G++ is less confusing (although still not as user-friendly as
EDG):
e2.cc:6:5: error: no match for 'operator+=' (operand types are 'E' and 'E')
6 | e += E1|E2;
| ~~^~~~~~~~
