enum.hpp

C++17 compile-time enum reflection library

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Content

• Requirements
• Installation
• Examples
• API
• Alternatives
• License

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Requirements

• clang >= 7
• gcc >= 7
• msvc >= 2019
• xcode >= 10.3

Installation

enum.hpp is a header-only library. All you need to do is copy the headers files from headers directory into your project and include them:

#include "enum.hpp/enum.hpp"

Also, you can add the root repository directory to your cmake project:

add_subdirectory(external/enum.hpp)
target_link_libraries(your_project_target PUBLIC enum.hpp)

Examples

• enum.hpp
  • Enum declarations
  • Traits using
  • Generic context
  • Adapting external enums
• enum_bitflags.hpp
  • Enum bitflags using
  • Additional bitflags functions

Enum declarations

// declaration of unscoped enumeration `debug_level` with traits

ENUM_HPP_DECL(debug_level, int,
    (level_info)
    (level_warning)
    (level_error))

/* equivalent to:

enum debug_level : int {
    level_info,
    level_warning,
    level_error,
};

struct debug_level_traits {
    ...
};*/

// declaration of scoped enumeration `color` with traits

ENUM_HPP_CLASS_DECL(color, unsigned,
    (red = 1 << 0)
    (green = 1 << 1)
    (blue = 1 << 2)
    (white = red | green | blue))

/* equivalent to:

enum class color : unsigned {
    red = 1 << 0,
    green = 1 << 1,
    blue = 1 << 2,
    white = red | green | blue,
};

struct color_traits {
    ...
};*/

Traits using

namespace
{
    ENUM_HPP_CLASS_DECL(color, unsigned,
        (red = 0xFF0000)
        (green = 0x00FF00)
        (blue = 0x0000FF)
        (white = red | green | blue))
}

int main() {
    // size
    static_assert(color_traits::size == 4);

    // to_underlying
    static_assert(color_traits::to_underlying(color::white) == 0xFFFFFF);

    // to_string
    static_assert(color_traits::to_string(color::red) == "red");
    static_assert(color_traits::to_string(color(42)) == std::nullopt);

    // from_string
    static_assert(color_traits::from_string("green") == color::green);
    static_assert(color_traits::from_string("error") == std::nullopt);

    // to_index
    static_assert(color_traits::to_index(color::blue) == 2);
    static_assert(color_traits::to_index(color(42)) == std::nullopt);

    // from_index
    static_assert(color_traits::from_index(2) == color::blue);
    static_assert(color_traits::from_index(42) == std::nullopt);

    // names
    for ( std::string_view n : color_traits::names ) {
        std::cout << n << ",";
    } // stdout: red,green,blue,

    return 0;
}

Generic context

namespace some_namespace
{
    ENUM_HPP_CLASS_DECL(color, unsigned,
        (red = 0xFF0000)
        (green = 0x00FF00)
        (blue = 0x0000FF)
        (white = red | green | blue))

    // register traits in enum namespace to generic access
    ENUM_HPP_REGISTER_TRAITS(color)
}

int main() {
    using color = some_namespace::color;

    // to string
    static_assert(enum_hpp::to_string(color::red) == "red");

    // from string
    static_assert(enum_hpp::from_string<color>("red") == color::red);

    return 0;
}

Adapting external enums

namespace external_ns
{
    enum class external_enum : unsigned short {
        a = 10,
        b,
        c = a + b
    };

    // should be in the same namespace
    ENUM_HPP_TRAITS_DECL(external_enum,
        (a)
        (b)
        (c))

    ENUM_HPP_REGISTER_TRAITS(external_enum)
}

int main() {
    using ee = external_ns::external_enum;
    static_assert(enum_hpp::to_string(ee::a) == "a");
    static_assert(enum_hpp::from_string<ee>("c") == ee::c);
    return 0;
}

Enum bitflags using

#include <enum.hpp/enum_bitflags.hpp>

namespace
{
    enum class perms : unsigned {
        execute = 1 << 0,
        write = 1 << 1,
        read = 1 << 2,
    };

    // declares operators for perms enum (~, |, &, ^)
    ENUM_HPP_OPERATORS_DECL(perms)
}

int main() {
    namespace bf = enum_hpp::bitflags;

    // every enum operator returns bitflags<enum> value
    bf::bitflags flags = perms::read | perms::write;

    // the bitflags class has some member functions for working with bit flags
    if ( flags.has(perms::write) ) {
        flags.clear(perms::write);
    }

    // you can passing other the same type bitflags to these functions
    flags.set(perms::write | perms::execute);

    // or using bit flags with the usual bit operations but type safe
    if ( flags & perms::execute ) {
        flags &= ~perms::execute; // flags.toggle(perms::execute);
    }

    // or compare them, why not?
    if ( flags == (perms::read | perms::write) ) {
        return 0;
    }

    return 1;
}

Additional bitflags functions

#include <enum.hpp/enum_bitflags.hpp>

namespace
{
    enum class perms : unsigned {
        execute = 1 << 0,
        write = 1 << 1,
        read = 1 << 2,
    };

    // declares operators for perms enum (~, |, &, ^)
    ENUM_HPP_OPERATORS_DECL(perms)
}

int main() {
    namespace bf = enum_hpp::bitflags;

    bf::bitflags<perms> flags = perms::read | perms::write;

    // bitflags namespace has many free functions
    // that can accept both enumerations and bit flags

    if ( bf::any_of(flags, perms::write | perms::execute) ) {
        // it's writable or executable
    }

    if ( bf::any_except(flags, perms::write | perms::execute) ) {
        // and something else :-)
    }
}

API

• enum.hpp
  • Enum traits
  • Enum generic functions
• enum_bitflags.hpp
  • Enum bitflags
  • Enum operators
  • Enum bitflags operators
  • Enum bitflags functions

Enum traits

// declares unscoped enumeration
ENUM_HPP_DECL(
    /*enum_name*/,
    /*underlying_type*/,
    /*fields*/)

// declares scoped enumeration
ENUM_HPP_CLASS_DECL(
    /*enum_name*/,
    /*underlying_type*/,
    /*fields*/)

// declares only traits for external enumerations
ENUM_HPP_TRAITS_DECL(
    /*enum_name*/,
    /*fields*/)

// declared enumeration traits
struct /*enum_name*/_traits {
    using enum_type = /*enum_name*/;
    using underlying_type = /*underlying_type*/;
    static constexpr std::size_t size = /*field_count*/;

    static constexpr const std::array<enum_type, size> values = {
        /*enum values*/
    };

    static constexpr const std::array<std::string_view, size> names = {
        /*enum value names*/
    };

    static constexpr underlying_type to_underlying(enum_type e) noexcept;

    static constexpr std::optional<std::string_view> to_string(enum_type e) noexcept;
    static constexpr std::string_view to_string_or_empty(enum_type e) noexcept;
    static std::string_view to_string_or_throw(enum_type e);

    static constexpr std::optional<enum_type> from_string(std::string_view name) noexcept;
    static constexpr enum_type from_string_or_default(std::string_view name, enum_type def) noexcept;
    static enum_type from_string_or_throw(std::string_view name);

    static constexpr std::optional<std::size_t> to_index(enum_type e) noexcept;
    static constexpr std::size_t to_index_or_invalid(enum_type e) noexcept;
    static std::size_t to_index_or_throw(enum_type e);

    static constexpr std::optional<enum_type> from_index(std::size_t index) noexcept;
    static constexpr enum_type from_index_or_default(std::size_t index, enum_type def) noexcept;
    static enum_type from_index_or_throw(std::size_t index);
};

Enum generic functions

// should be in enum namespace
ENUM_HPP_REGISTER_TRAITS(/*declared_enum_name*/)

namespace enum_hpp
{
    template < typename Enum >
    using traits_t = typename traits<Enum>::type;

    template < typename Enum >
    using underlying_type = typename traits_t<Enum>::underlying_type;

    template < typename Enum >
    constexpr std::size_t size() noexcept;

    template < typename Enum >
    constexpr const std::array<Enum, size<Enum>()>& values() noexcept;

    template < typename Enum >
    constexpr const std::array<std::string_view, size<Enum>()>& names() noexcept;

    template < typename Enum >
    constexpr typename traits_t<Enum>::underlying_type to_underlying(Enum e) noexcept;

    template < typename Enum >
    constexpr std::optional<std::string_view> to_string(Enum e) noexcept;

    template < typename Enum >
    constexpr std::string_view to_string_or_empty(Enum e) noexcept;

    template < typename Enum >
    std::string_view to_string_or_throw(Enum e);

    template < typename Enum >
    constexpr std::optional<Enum> from_string(std::string_view name) noexcept;

    template < typename Enum >
    constexpr Enum from_string_or_default(std::string_view name, Enum def) noexcept;

    template < typename Enum >
    Enum from_string_or_throw(std::string_view name);

    template < typename Enum >
    constexpr std::optional<std::size_t> to_index(Enum e) noexcept;

    template < typename Enum >
    constexpr std::size_t to_index_or_invalid(Enum e) noexcept;

    template < typename Enum >
    std::size_t to_index_or_throw(Enum e);

    template < typename Enum >
    constexpr std::optional<Enum> from_index(std::size_t index) noexcept;

    template < typename Enum >
    constexpr Enum from_index_or_default(std::size_t index, Enum def) noexcept;

    template < typename Enum >
    Enum from_index_or_throw(std::size_t index);
}

Enum bitflags

namespace enum_hpp::bitflags
{
    template < typename Enum >
    class bitflags final {
    public:
        using enum_type = Enum;
        using underlying_type = std::underlying_type_t<Enum>;

        bitflags() = default;
        bitflags(const bitflags&) = default;
        bitflags& operator=(const bitflags&) = default;

        constexpr bitflags(enum_type flags);
        constexpr explicit bitflags(underlying_type flags);

        constexpr void swap(bitflags& other) noexcept;
        constexpr explicit operator bool() const noexcept;

        constexpr underlying_type as_raw() const noexcept;
        constexpr enum_type as_enum() const noexcept;

        constexpr bool has(bitflags flags) const noexcept;
        constexpr bitflags& set(bitflags flags) noexcept;
        constexpr bitflags& toggle(bitflags flags) noexcept;
        constexpr bitflags& clear(bitfl