Source/WTF/wtf/EnumTraits.h

/*
 * Copyright (C) 2016 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
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 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
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 */

#pragma once

#include <type_traits>

namespace WTF {

template<typename> struct EnumTraits;

template<typename E, E...> struct EnumValues;

template<typename T, typename E> struct EnumValueChecker;

template<typename T, typename E, E e, E... es>
struct EnumValueChecker<T, EnumValues<E, e, es...>> {
    static constexpr bool isValidEnum(T t)
    {
        return (static_cast<T>(e) == t) ? true : EnumValueChecker<T, EnumValues<E, es...>>::isValidEnum(t);
    }
};

template<typename T, typename E>
struct EnumValueChecker<T, EnumValues<E>> {
    static constexpr bool isValidEnum(T)
    {
        return false;
    }
};

template<typename E, typename T, typename = std::enable_if_t<!std::is_same_v<std::underlying_type_t<E>, bool>>>
constexpr auto isValidEnum(T t) -> decltype(EnumValueChecker<T, typename EnumTraits<E>::values>::isValidEnum(t), bool())
{
    static_assert(sizeof(T) >= sizeof(std::underlying_type_t<E>), "Integral type must be at least the size of the underlying enum type");

    return EnumValueChecker<T, typename EnumTraits<E>::values>::isValidEnum(t);
}

template<typename E, typename T, typename = std::enable_if_t<!std::is_same_v<std::underlying_type_t<E>, bool>>>
auto isValidEnum(T t) -> decltype(EnumTraits<E>::isValidEnum(t), bool())
{
    return EnumTraits<E>::isValidEnum(t);
}

template<typename E, typename T, typename = std::enable_if_t<std::is_same_v<std::underlying_type_t<E>, bool>>>
constexpr bool isValidEnum(T t)
{
    return !t || t == 1;
}

template<typename E>
constexpr auto enumToUnderlyingType(E e)
{
    return static_cast<std::underlying_type_t<E>>(e);
}

}

using WTF::isValidEnum;