Working as intended? Named combined bitflags cannot be casted to

[JWCS]

I believe this is related to #314 and #321, so my apologies if it is. But, from the docs and those comments, it almost seemed like the below use case should work; but it fails for the BOTH case. This is after I considered your casting comments in 314 about enum vs enum_flags, and accounted for both input formats, to try both in what seemed the least restrictive way. I also read through the limitations... so I am very confused. Working off of head (0.9.6):

#include <magic_enum_flags.hpp>
#include <iostream>
#include <string>

enum class FlowDirection : unsigned {
    NONE  = 0,
    CCW   = 1,
    CW    = 2,
    BOTH  = 3,
};
template <>
struct magic_enum::customize::enum_range<FlowDirection> {
  static constexpr bool is_flags = true;
};
inline static FlowDirection FlowDirection_read(
    std::string const& str, FlowDirection const& def = FlowDirection::NONE)
{
  return magic_enum::enum_flags_cast<FlowDirection>(str, magic_enum::case_insensitive).value_or(
      magic_enum::enum_cast<FlowDirection>(str, magic_enum::case_insensitive).value_or(def));
}

static void test(std::string const& str){
    FlowDirection flow = FlowDirection_read(str);
    std::cout << str << " ("
      << magic_enum::enum_name(flow) << "/"
      << magic_enum::enum_flags_name(flow) << "): "
      << magic_enum::enum_integer(flow) << std::endl;
}

int main(){
    test("CCW");
    test("ccw");
    test("cw");
    test("BOTH");
    test("NONE");
    test("NONE|CCW");
    test("CCW|CW");
    return 0;
}

Which results in incorrect values definitely for BOTH, and a curious non-parsing (?) for "NONE|CCW"

> g++ -std=gnu++17 demo.cpp && ./a.out
CCW (CCW/CCW): 1    # OK
ccw (CCW/CCW): 1    # OK
cw (CW/CW): 2       # OK
BOTH (/): 0         # Uhhhhh help?? I have no clue what I'm doing wrong, to not get this.
NONE (/): 0         # This is interesting; the value is correct, but the name is missing; which might be 321
NONE|CCW (/): 0     # Uh, I don't think I need this, but, is this a bug?
CCW|CW (/CCW|CW): 3 # OK

[Neargye]

BOTH (/): 0 - https://github.com/Neargye/magic_enum/issues/314#issuecomment-1812285880. BOTH is not true flag, it is a "flag or"

NONE (/): 0 - https://github.com/Neargye/magic_enum/issues/321

NONE|CCW (/): 0 - will check, looks like bug, expected 1

[JWCS]

With respect to the first one, BOTH, the reason for my confusion is that the read() function attempts both (in order) enum_flags_cast and then enum_cast. As per the relevant docs/comment in 314:

enum class TestEnum {
A = 0,
B = 1,
C = 2,
D = 3,
};

enum_name(TestEnum::D) = 'D'; vs enum_flags_name(TestEnum::D) = 'B|C';
enum_flags_cast('A') = nullopt; vs enum_cast('A') = TestEnum::A;
enum_flags_cast('D') = nullopt; vs enum_flags_cast('B|C') = TestEnum::D; vs  enum_cast('D') = TestEnum::D;

I'd expect enum_flags_cast('D' /* BOTH */).value_or( enum_cast('D') to fail on flag-cast D (since not a real flag), but then trying to normal enum cast D to work (enum_cast('D') == TestEnum::D) (and the resulting integer TestEnum::D == TestEnum::B | TestEnum::C). I tried it like this, such that if the string 'B|C' was passed, that would first get correctly parsed/handled, but if the shorthand 'BOTH' was passed, that would also get correctly handled. My main question is, is there something I'm missing, that test("BOTH") -> enum_flags_cast("BOTH") /* fail */ .value_or( enum_cast("BOTH") /* fail */ .value_or("NONE") /* incorrect!? */ ). Does it have something to do with

template <>
struct magic_enum::customize::enum_range<FlowDirection> {
  static constexpr bool is_flags = true;
};

?

[ZXShady]

The behavior you seeing is indeed related to how is_flags affects the different functions.

1. enum_flags_* functions · These functions always treat the enum as flags (regardless of is_flags setting) · They only recognize values that are direc powers of 2 this is why BOTH (3) isn't recognized.

2. regular enum functions · these are affected by the is_flags customization point. · when is_flags is true, they only show power of 2 values (like enum_flags_*) · when is_flags is false, they reflect the normal range [-128,127].

In your case:

· With is_flags is true, neither function will recognize BOTH (3) because: · enum_flags_* never recognizes combined enum member flags (not powers of 2) nor zero. · regular enum_* skips it because is_flags is true, behaving like enum_flags_.* · NONE shows as empty because for enums where is_flags is true skips the 0 value.

· "NONE|CCW" parsing to 0 is weird but expected given magic_enum does not reflect 0 value for flags, it thinks NONE is an invalid enum member.

[Neargye]

@JWCS @ZXShady

After checking, yes, "NONE|CCW" parsing to 0 in the current implementation is not a bug. Library doesn't find NONE in the flags list and treats it as an invalid name.

Personally, I don't think zero should be included by default. I would prefer two separate options: flags and flags_with_zero (or flags_and_zero), though this is open for discussion.