cpp-opaque-typedef/include/opaque_typedef/comparable.hpp

#pragma once

namespace types {
  template <typename Self> struct EqualityComparable {
    friend bool operator==(Self const & lhs, Self const & rhs) {
      return lhs.get() == rhs.get();
    }
    friend bool operator!=(Self const & lhs, Self const & rhs) {
      return !(lhs == rhs);
    }

#if __cplusplus >= 202002L
    friend std::partial_ordering operator<=>(Self const & lhs,
                                             Self const & rhs) {
      return lhs == rhs ? std::partial_ordering::equivalent
                        : std::partial_ordering::unordered;
    }
#endif
  };

  template <typename Self> struct Comparable {
    friend bool operator==(Self const & lhs, Self const & rhs) {
      return lhs.get() == rhs.get();
    }
    friend bool operator!=(Self const & lhs, Self const & rhs) {
      return !(lhs == rhs);
    }
    friend bool operator<(Self const & lhs, Self const & rhs) {
      return lhs.get() < rhs.get();
    }
    friend bool operator>(Self const & lhs, Self const & rhs) {
      return rhs.get() < lhs.get();
    }
    friend bool operator<=(Self const & lhs, Self const & rhs) {
      return !(rhs.get() < lhs.get());
    }
    friend bool operator>=(Self const & lhs, Self const & rhs) {
      return !(lhs.get() < rhs.get());
    }

#if __cplusplus >= 202002L
    friend auto operator<=>(Self const & lhs, Self const & rhs) {
      return lhs.get() <=> rhs.get();
    }
#endif
  };
}