Function hash_combine_

example/json.hpp:115–119

        // Hashing.

        inline std::size_t
        hash_combine_(std::size_t seed, std::size_t value) noexcept
        {
            return seed ^= value + 0x9e3779b9 + (seed << 6) + (seed >> 2);
        }

        // Why on earth!?  It turns out that Clang's unique_ptr is (at least
        // sometimes) the size of two pointers, which is simply unreasonable.