https://en.cppreference.com/w/cpp/utility/compare/three_way_comparable std::three_way_comparable, std::three_way_comparable_with - cppreference.com template concept three_way_comparable = __WeaklyEqualityComparableWith && __PartiallyOrderedWith && requires(const std::remove_reference_t & a, const std::remove_reference_ en.cppreference.com 공식 문서는 위쪽. ..