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* Special case bool in cmp_less to avoid msvc's warnings

* Fix underflow in out of range check

The previous fix addressed bool but it seems that was not the heart
of the issue.

The problem is that (lhs - 1) can underflow.

Another example of the check trigger when it shouldn't is:
uint8_t with min_value set to 0 and a value of uint8_t::max
lhs-1 would underflow and find max (see added test).

The issue happens when lhs == rhs. To avoid that situation: flip the if-else!
`cmp_less(rhs, lhs)`means that rhs is strictly less than lhs, so
the check will not trigger when lhs == rhs.

Also, cleanup the bool special-case, as it is no longer necessary.

Note: for the bug to manifest, it is important that the min
of the enums is customized to be 0, so corresponding enum_range
specializations need to be present in the regression tests.
41c9164

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Magic Enum C++

Header-only C++17 library provides static reflection for enums, work with any enum type without any macro or boilerplate code.

  • enum_cast obtains enum value from string or integer.
  • enum_value returns enum value at specified index.
  • enum_values obtains enum value sequence.
  • enum_count returns number of enum values.
  • enum_integer obtains integer value from enum value.
  • enum_name returns name from enum value.
  • enum_names obtains string enum name sequence.
  • enum_entries obtains pair (value enum, string enum name) sequence.
  • enum_index obtains index in enum value sequence from enum value.
  • enum_contains checks whether enum contains enumerator with such value.
  • enum_type_name returns name of enum type.
  • is_unscoped_enum checks whether type is an Unscoped enumeration.
  • is_scoped_enum checks whether type is an Scoped enumeration.
  • underlying_type improved UB-free "SFINAE-friendly" underlying_type.
  • ostream_operators ostream operators for enums.
  • bitwise_operators bitwise operators for enums.

Documentation

Features

  • C++17
  • Header-only
  • Dependency-free
  • Compile-time
  • Enum to string
  • String to enum
  • Iterating over enum

Examples

// For example color enum.
enum class Color { RED = 2, BLUE = 4, GREEN = 8 };
  • Enum value to string

    Color color = Color::RED;
    auto color_name = magic_enum::enum_name(color);
    // color_name -> "RED"
  • String to enum value

    std::string color_name{"GREEN"};
    auto color = magic_enum::enum_cast<Color>(color_name);
    if (color.has_value()) {
      // color.value() -> Color::GREEN
    }
  • Integer to enum value

    int color_integer = 2;
    auto color = magic_enum::enum_cast<Color>(color_integer);
    if (color.has_value()) {
      // color.value() -> Color::RED
    }
  • Indexed access to enum value

    std::size_t i = 1;
    Color color = magic_enum::enum_value<Color>(i);
    // color -> Color::BLUE
  • Enum value sequence

    constexpr auto& colors = magic_enum::enum_values<Color>();
    // colors -> {Color::RED, Color::BLUE, Color::GREEN}
    // colors[0] -> Color::RED
  • Number of enum elements

    constexpr std::size_t color_count = magic_enum::enum_count<Color>();
    // color_count -> 3
  • Enum value to integer

    Color color = Color::RED;
    auto color_integer = magic_enum::enum_integer(color);
    // color -> 2
  • Enum names sequence

    constexpr auto& color_names = magic_enum::enum_names<Color>();
    // color_names -> {"RED", "BLUE", "GREEN"}
    // color_names[0] -> "RED"
  • Enum entries sequence

    constexpr auto& color_entries = magic_enum::enum_entries<Color>();
    // color_entries -> {{Color::RED, "RED"}, {Color::BLUE, "BLUE"}, {Color::GREEN, "GREEN"}}
    // color_entries[0].first -> Color::RED
    // color_entries[0].second -> "RED"
  • Ostream operator for enum

    using namespace magic_enum::ostream_operators; // out-of-the-box ostream operators for enums.
    Color color = Color::BLUE;
    std::cout << color << std::endl; // "BLUE"
  • Bitwise operator for enum

    enum class Flags { A = 1 << 0, B = 1 << 1, C = 1 << 2, D = 1 << 3 };
    using namespace magic_enum::bitwise_operators; // out-of-the-box bitwise operators for enums.
    // Support operators: ~, |, &, ^, |=, &=, ^=.
    Flags flags = Flags::A | Flags::B & ~Flags::C;
  • Checks whether type is an Unscoped enumeration.

    enum color { red, green, blue };
    enum class direction { left, right };
    
    magic_enum::is_unscoped_enum<color>::value -> true
    magic_enum::is_unscoped_enum<direction>::value -> false
    magic_enum::is_unscoped_enum<int>::value -> false
    
    // Helper variable template.
    magic_enum::is_unscoped_enum_v<color> -> true
  • Checks whether type is an Scoped enumeration.

    enum color { red, green, blue };
    enum class direction { left, right };
    
    magic_enum::is_scoped_enum<color>::value -> false
    magic_enum::is_scoped_enum<direction>::value -> true
    magic_enum::is_scoped_enum<int>::value -> false
    
    // Helper variable template.
    magic_enum::is_scoped_enum_v<direction> -> true
  • Static storage enum variable to string This version is much lighter on the compile times and is not restricted to the enum_range limitation.

    constexpr Color color = Color::BLUE;
    constexpr auto color_name = magic_enum::enum_name<color>();
    // color_name -> "BLUE"

Remarks

  • magic_enum does not pretend to be a silver bullet for reflection for enums, it was originally designed for small enum.

  • Before use, read the limitations of functionality.

  • For the small enum use the API from the namespace magic_enum, and for enum-flags use the API from the namespace magic_enum::flags.

Integration

  • You should add the required file magic_enum.hpp.

  • If you are using vcpkg on your project for external dependencies, then you can use the magic-enum package.

  • If you are using Conan to manage your dependencies, merely add magic_enum/x.y.z to your conan's requires, where x.y.z is the release version you want to use.

  • If you are using Build2 to build and manage your dependencies, add depends: magic_enum ^x.y.z to the manifest file where x.y.z is the release version you want to use. You can then import the target using magic_enum%lib{magic_enum}.

  • Alternatively, you can use something like CPM which is based on CMake's Fetch_Content module.

    CPMAddPackage(
        NAME magic_enum
        GITHUB_REPOSITORY Neargye/magic_enum
        GIT_TAG x.y.z # Where `x.y.z` is the release version you want to use.
    )
  • Bazel is also supported, simply add to your WORKSPACE file:

    http_archive(
        name = "magic_enum",
        strip_prefix = "magic_enum-<commit>",
        urls = ["https://github.com/Neargye/magic_enum/archive/<commit>.zip"],
    )
    

    To use bazel inside the repository it's possible to do:

    bazel build //...
    bazel test //...
    bazel run //:example
    

    (Note that you must use a supported compiler or specify it with export CC= <compiler>.)

Compiler compatibility

  • Clang/LLVM >= 5
  • MSVC++ >= 14.11 / Visual Studio >= 2017
  • Xcode >= 10
  • GCC >= 9
  • MinGW >= 9

Licensed under the MIT License