Function operator()

examples/server/json.hpp:24343–24346

struct hash<nlohmann::NLOHMANN_BASIC_JSON_TPL>
{
    std::size_t operator()(const nlohmann::NLOHMANN_BASIC_JSON_TPL& j) const
    {
        return nlohmann::detail::hash(j);
    }
};

// specialization for std::less<value_t>