ClickHouse/base/common/strong_typedef.h

#pragma once

#include <type_traits>

template <class T, class Tag>
struct StrongTypedef
{
private:
    using Self = StrongTypedef;
    T t;

public:
    template <class Enable = typename std::is_copy_constructible<T>::type>
    explicit StrongTypedef(const T & t_) : t(t_) {}
    template <class Enable = typename std::is_move_constructible<T>::type>
    explicit StrongTypedef(T && t_) : t(std::move(t_)) {}

    template <class Enable = typename std::is_default_constructible<T>::type>
    StrongTypedef(): t() {}

    StrongTypedef(const Self &) = default;
    StrongTypedef(Self &&) = default;

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

    template <class Enable = typename std::is_copy_assignable<T>::type>
    Self & operator=(const T & rhs) { t = rhs; return *this;}

    template <class Enable = typename std::is_move_assignable<T>::type>
    Self & operator=(T && rhs) { t = std::move(rhs); return *this;}

    operator const T & () const { return t; }
    operator T & () { return t; }

    bool operator==(const Self & rhs) const { return t == rhs.t; }
    bool operator<(const Self & rhs) const { return t < rhs.t; }

    T & toUnderType() { return t; }
    const T & toUnderType() const { return t; }
};

namespace std
{
    template <class T, class Tag>
    struct hash<StrongTypedef<T, Tag>>
    {
        size_t operator()(const StrongTypedef<T, Tag> & x) const
        {
            return std::hash<T>()(x.toUnderType());
        }
    };
}

#define STRONG_TYPEDEF(T, D) \
    struct D ## Tag {}; \
    using D = StrongTypedef<T, D ## Tag>; \