Named tuple for C++

NamedTuple.h

// Named tuple for C++
// Example code from http://vitiy.info/
// Written by Victor Laskin (victor.laskin@gmail.com)

// Parts of code were taken from: https://gist.github.com/Manu343726/081512c43814d098fe4b

namespace foonathan {
    namespace string_id {
        namespace detail
        {
            using hash_type = std::uint64_t;
            
            constexpr hash_type fnv_basis = 14695981039346656037ull;
            constexpr hash_type fnv_prime = 109951162821ull;
            
            // FNV-1a 64 bit hash
            constexpr hash_type sid_hash(const char *str, hash_type hash = fnv_basis) noexcept
            {
                return *str ? sid_hash(str + 1, (hash ^ *str) * fnv_prime) : hash;
            }
        }
    }
} // foonathan::string_id::detail


    namespace fn_detail {
        
        /// Named parameter (could be empty!)
        template <typename Hash, typename... Ts>
        struct named_param {
            using hash = Hash;                                                  ///< key
            std::tuple<Ts...> value;                                            ///< param's data itself
            
            named_param(Ts&&... ts) : value(std::forward<Ts>(ts)...){ };        ///< constructor
            
            template <typename P>
            named_param<Hash,P> operator=(P&& p){ return named_param<Hash,P>(std::forward<P>(p)); };
            
            
            
        };
    
        template <typename Hash>
        using make_named_param = named_param<Hash>;
        
        

        
        /// Named tuple is just tuple of named params
        template <typename... Params>
        struct named_tuple : public std::tuple<Params...>
        {
            
            template <typename... Args>
            named_tuple(Args&&... args) : std::tuple<Args...>(std::forward<Args>(args)...) {}
            
            static const std::size_t error = -1;
            
            template<std::size_t I = 0, typename Hash>
            constexpr typename std::enable_if<I == sizeof...(Params), const std::size_t>::type
            static get_element_index()
            {
                return error;
            }
            
            template<std::size_t I = 0, typename Hash>
            constexpr typename std::enable_if<I < sizeof...(Params), const std::size_t>::type
            static get_element_index()
            {
                using elementType = typename std::tuple_element<I, std::tuple<Params...>>::type;
                //return (typeid(typename elementType::hash) == typeid(Hash)) ? I : get_element_index<I + 1, Hash>();
                return (std::is_same<typename elementType::hash, Hash>::value) ? I : get_element_index<I + 1, Hash>();
            }
            
            template<typename Hash>
            const auto& get() const
            {
                constexpr std::size_t index = get_element_index<0, Hash>();
                static_assert((index != error), "Wrong named tuple key");
                auto& param = (std::get< index >(static_cast<const std::tuple<Params...>&>(*this)));
                return std::get<0>( param.value );
            }
            
            template<typename NP>
            const auto& operator[](NP&& param)
            {
                return get<typename NP::hash>();
            }
             
        };
        
            
    }
    
    template <typename... Args>
    auto make_named_tuple(Args&&... args)
    {
        return fn_detail::named_tuple<Args...>(std::forward<Args>(args)...);
    }
    
#define param(x) fn_detail::make_named_param< std::integral_constant<foonathan::string_id::detail::hash_type, foonathan::string_id::detail::sid_hash(x)> >{}