limitations.md

Limitations

• This library uses a compiler-specific hack based on __PRETTY_FUNCTION__ / __FUNCSIG__.

• To check if magic_enum is supported with your compiler, use macro MAGIC_ENUM_SUPPORTED or constexpr constant magic_enum::is_magic_enum_supported. If magic_enum is used on an unsupported compiler, a compilation error will occur. To suppress the error, define macro MAGIC_ENUM_NO_CHECK_SUPPORT.

• magic_enum can't reflect if the enum is a forward declaration.

Enum Flags

• For enum flags, add is_flags to specialization enum_range for necessary enum type. Specializations of enum_range must be injected in namespace magic_enum::customize.

  enum class Directions { Up = 1 << 0, Down = 1 << 1, Right = 1 << 2, Left = 1 << 3 };
  template <>
  struct magic_enum::customize::enum_range<Directions> {
    static constexpr bool is_flags = true;
  };

• MAGIC_ENUM_RANGE_MAX / MAGIC_ENUM_RANGE_MIN does not affect the maximum number of enum flags.

• If an enum is declared as a flag enum, its zero value will not be reflected.

Enum Range

• Enum values must be in the range [MAGIC_ENUM_RANGE_MIN, MAGIC_ENUM_RANGE_MAX].

• By default, MAGIC_ENUM_RANGE_MIN = -128, MAGIC_ENUM_RANGE_MAX = 127.

• If you need a different range for all enum types by default, redefine the macro MAGIC_ENUM_RANGE_MIN and MAGIC_ENUM_RANGE_MAX:

  #define MAGIC_ENUM_RANGE_MIN 0
  #define MAGIC_ENUM_RANGE_MAX 256
  #include <magic_enum/magic_enum.hpp>

• If you need a different range for a specific enum type, add the specialization enum_range for the enum type. Specializations of enum_range must be injected in namespace magic_enum::customize.

  #include <magic_enum/magic_enum.hpp>
  
  enum class number { one = 100, two = 200, three = 300 };
  
  template <>
  struct magic_enum::customize::enum_range<number> {
    static constexpr int min = 100;
    static constexpr int max = 300;
    // (max - min) must be less than UINT16_MAX.
  };

Aliasing

magic_enum won't work if a value is aliased. How magic_enum works with aliases is compiler-implementation-defined.

enum ShapeKind {
  ConvexBegin = 0,
  Box = 0, // Won't work.
  Sphere = 1,
  ConvexEnd = 2,
  Donut = 2, // Won't work too.
  Banana = 3,
  COUNT = 4
};
// magic_enum::enum_cast<ShapeKind>("Box") -> nullopt
// magic_enum::enum_name(ShapeKind::Box) -> "ConvexBegin"

One possible workaround for the issue is to define the enum values you want reflected before their aliases:

enum ShapeKind {
  // Convex shapes, see ConvexBegin and ConvexEnd below.
  Box = 0,
  Sphere = 1,

  // Non-convex shapes.
  Donut = 2,
  Banana = 3,

  COUNT = Banana + 1,

  // Non-reflected aliases.
  ConvexBegin = Box,
  ConvexEnd = Sphere + 1
};
// magic_enum::enum_cast<ShapeKind>("Box") -> ShapeKind::Box
// magic_enum::enum_name(ShapeKind::Box) -> "Box"

// Non-reflected aliases.
// magic_enum::enum_cast<ShapeKind>("ConvexBegin") -> nullopt
// magic_enum::enum_name(ShapeKind::ConvexBegin) -> "Box"

On some compilers, enum aliases are not supported, for example Visual Studio 2017, macro MAGIC_ENUM_SUPPORTED_ALIASES will be undefined.

enum Number {
  one = 1,
  ONE = 1
};
// magic_enum::enum_cast<Number>("one") -> nullopt
// magic_enum::enum_name(Number::one) -> ""
// magic_enum::enum_cast<Number>("ONE") -> nullopt
// magic_enum::enum_name(Number::ONE) -> ""

Other Compiler Issues

• If you hit a message like this:

  [...]
  note: constexpr evaluation hit maximum step limit; possible infinite loop?
  

  Change the limit for the number of constexpr evaluated:

  • MSVC: /constexpr:depthN, /constexpr:stepsN https://docs.microsoft.com/en-us/cpp/build/reference/constexpr-control-constexpr-evaluation
  • Clang: -fconstexpr-depth=N, -fconstexpr-steps=N https://clang.llvm.org/docs/UsersManual.html#controlling-implementation-limits
  • GCC: -fconstexpr-depth=N, -fconstexpr-loop-limit=N, -fconstexpr-ops-limit=N https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/C_002b_002b-Dialect-Options.html

• Visual Studio's Intellisense may have some problems analyzing magic_enum.

• Enums in templates may not work correctly (especially on Сlang). See #164, #65