magic_enum/doc/limitations.md

Limitations

• To check is magic_enum supported compiler use macro MAGIC_ENUM_SUPPORTED or constexpr constant magic_enum::is_magic_enum_supported.

• This library uses a compiler-specific hack (based on __PRETTY_FUNCTION__ / __FUNCSIG__), which works on Clang >= 5, MSVC >= 15.3 and GCC >= 9.

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

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

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

  • MAGIC_ENUM_RANGE_MIN must be less or equals than 0 and must be greater than INT16_MIN.

  • MAGIC_ENUM_RANGE_MAX must be greater than 0 and must be less than INT16_MAX.

  • If need another 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.hpp>
    

  • If need another range for specific enum type, add specialization enum_range for necessary enum type. Specialization of enum_range must be injected in namespace magic_enum::customize.

    #include <magic_enum.hpp>
    
    enum class number { one = 100, two = 200, three = 300 };
    
    namespace magic_enum::customize {
    template <>
    struct enum_range<number> {
      static constexpr int min = 100; // Must be greater than `INT16_MIN`.
      static constexpr int max = 300; // Must be less than `INT16_MAX`.
    };
    } // namespace magic_enum
    

• magic_enum won't work if a value is aliased. Work with enum-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") -> std::nullopt or ShapeKind::Box
  // magic_enum::enum_name(ShapeKind::Box) -> "ConvexBegin" or ""
  

  One of the possible workaround the issue:

  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") -> std::nullopt
  // magic_enum::enum_name(ShapeKind::ConvexBegin) -> "Box"
  

  On some compiler enum-aliases not supported, for example Visual Studio 2017.

  It is possible to check whether enum-aliases supported using a macro MAGIC_ENUM_SUPPORTED_ALIASES.

• 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

• Intellisense Visual Studio may have some problems analyzing magic_enum.