tagged.hpp

#ifndef tagged_hpp_
#define tagged_hpp_
 
#include <concepts>
#include <tuple>
#include <ostream>
#include <vector>
#include <variant>
 
namespace tagged {

 
    // TAG
 
    namespace impl {
        template< typename T>
        struct tag_traits;
    }

    template< typename T>
    concept tag = impl::tag_traits<T>::is_tag;

    template< typename T>
    concept selector_tag = impl::tag_traits<T>::is_selector;

    template< tag T>
    using selector = typename impl::tag_traits<T>::selector;

    template< typename T1, typename T2>
    concept same_selector = std::same_as< selector<T1>, selector<T2>>;
 
    struct tag_base {};
 
    namespace impl {
        template< typename T>
        requires T::is_tag
        struct tag_traits<T>
        {
            static constexpr bool is_tag = true;
            static constexpr bool is_direct = false;
            using core = typename T::core;
            static constexpr bool is_selector = T::is_selector;
            using selector = typename T::selector;
            template<selector_tag T2>
            using retag = typename T::template retag<T2>;
        };
 
        template< typename T>
            requires std::derived_from<T, tag_base>
        struct tag_traits<T>
        {
            static constexpr bool is_tag = true;
            static constexpr bool is_direct = true;
            using core = T;
            static constexpr bool is_selector = true;
            using selector = T;
            template<selector_tag T2>
            using retag = T2;
        };
    };
 
    template< tag T>
    using core = typename impl::tag_traits<T>::core;
 
    template< typename T1, typename T2>
    concept same_tag = std::same_as< core<T1>, core<T2>>;
 
    template< selector_tag T2, tag T>
    using retag = typename impl::tag_traits<T>::template retag<T2>;
 
    template< tag T, std::size_t b, std::size_t e>
    struct sr_tag {
        static constexpr bool is_tag = true;
        static constexpr bool is_direct = false;
        using core = sr_tag< T, b, e>;
        static constexpr bool is_selector = false;
        using selector = T;
        template<selector_tag T2>
        using retag = sr_tag< T2, b, e>;
 
        static constexpr bool is_static = true;
        static constexpr std::size_t begin = b;
        static constexpr std::size_t end = e;
    };
 
    template< typename T>
    concept static_tag = tag<T> && T::is_static;
 
    template< typename T>
    concept non_static_tag = tag<T> && (!static_tag<T>);
 
    // CARRIER
 
    template< tag T>
    using index_carrier_type = std::size_t;

    template< tag ... TL>
    class index_class;
 
    template< tag ... TL>
    class iterator_class;
 
    template< tag ... TL>
    class range_class;
 
    template< typename E, tag ... TL>
    class tensor_view;

    namespace impl {
        struct range_base {};
    }
 
    template< typename T>
    concept is_range = std::derived_from< T, impl::range_base>;
    
    namespace impl {
        struct index_base {};
 
        template< tag T, tag ... TL>
        struct element_traits;
 
        template< tag T>
        struct element_traits< T> : std::false_type {};
 
        template< tag T, tag T2, tag ... TL>
            requires same_selector<T, T2>
        struct element_traits< T, T2, TL ...> : std::true_type {};
 
        template< tag T, tag T2, tag ... TL>
            requires (!same_selector<T, T2>)
        struct element_traits< T, T2, TL ...> : element_traits< T, TL ...> {};
 
        template< typename T, typename ... TL>
        concept one_of = element_traits< T, TL...>::value;
 
        template< tag T, tag ... TL>
        struct position_traits;
 
        template< tag T, tag T2, tag ... TL>
            requires same_selector<T, T2>
        struct position_traits< T, T2, TL ...>
            : std::integral_constant< std::size_t, 0>
        {};
 
        template< tag T, tag T2, tag ... TL>
            requires (!same_selector<T, T2>)
        struct position_traits< T, T2, TL ...>
            : std::integral_constant< std::size_t, position_traits< T, TL ...>::value + 1>
        {};
 
        template< typename T, typename ... TL>
        inline constexpr std::size_t position_of = position_traits< T, TL...>::value;
    }

    template< typename ... TL>
    struct tag_list {};
    
    namespace impl {
        template< typename TA, typename TB>
        struct concat_traits;
            
        template< tag TA, tag TB>
        struct concat_traits< TA, TB> {
            using type = tag_list< TA, TB>;
        };
 
        template< tag TA, tag ... LB>
        struct concat_traits< TA, tag_list< LB ...>> {
            using type = tag_list< TA, LB ...>;
        };
 
        template< typename TA, typename TB>
        using concat_list = typename concat_traits< TA, TB>::type;
 
        template< typename LA, typename LB>
        struct subtract_traits;
 
        template< tag ... TLA>
        struct subtract_traits< tag_list<TLA...>, tag_list<>> {
            using type = tag_list<TLA...>;
        };
 
        template< tag TA, tag ... TLA, tag TB>
        requires same_selector< TA, TB>
        struct subtract_traits< tag_list<TA, TLA...>, tag_list<TB>>
        {
            using type = tag_list<TLA ...>;
        };
 
        template< tag TA, tag ... TLA, tag TB>
            requires (!same_selector< TA, TB>)
        struct subtract_traits< tag_list<TA, TLA...>, tag_list<TB>>
        {
        private:
            using removed_a = typename subtract_traits< tag_list<TLA ...>, tag_list<TB>>::type;
        public:
            using type = concat_list< TA, removed_a>;
        };
 
        template< tag ... TLA, tag TB, tag ... TLB>
        struct subtract_traits< tag_list<TLA...>, tag_list<TB, TLB...>>
        {
        private:
            using removed_a = typename subtract_traits<tag_list<TLA...>, tag_list<TB>>::type;
        public:
            using type = typename subtract_traits<removed_a, tag_list<TLB ...>>::type;
        };
 
        template< selector_tag T, tag ... TL>
        struct pick_traits;
 
        template< selector_tag T, tag T0, tag ... TL>
            requires same_selector<T, T0>
        struct pick_traits< T, T0, TL ...>
        {
            using type = T0;
        };
 
        template< selector_tag T, tag T0, tag ... TL>
            requires (!same_selector<T, T0>)
        struct pick_traits< T, T0, TL ...>
            : pick_traits< T, TL ...>
        {};
 
        template< std::size_t I, tag ... TL>
        struct pick_index_traits;
 
        template< tag T0, tag ... TL>
        struct pick_index_traits< 0, T0, TL ...>
        {
            using type = T0;
        };
 
        template< std::size_t I, tag T0, tag ... TL>
        struct pick_index_traits< I, T0, TL ...>
            : pick_index_traits< I-1, TL ...>
        {};
 
        template< typename A, typename B>
        struct same_list_traits;
 
        template< tag ... AL, tag ... BL>
            requires (sizeof...(AL) == sizeof...(BL))
        struct same_list_traits< tag_list<AL...>, tag_list<BL...>>
        {
            static constexpr bool value = (same_selector<AL, BL> && ...);
        };
 
        template< typename A, typename B>
        concept same_selector_list = same_list_traits< A, B>::value;
 
        template< typename A, typename B>
        struct subset_traits;
 
        template< tag ... AL, tag ... BL>
        struct subset_traits< tag_list<AL...>, tag_list<BL...>>
        {
            static constexpr bool value = (one_of<AL, BL...> && ...);
        };
 
        template< typename A, typename B>
        concept subset_selector = subset_traits< A, B>::value;
    }
 
    template< typename T, typename ... TL>
    requires impl::one_of<T, TL...>
    using pick = typename impl::pick_traits< T, TL...>::type;
 
    template< std::size_t I, typename ... TL>
    requires (I < sizeof...(TL))
    using pick_index = typename impl::pick_index_traits< I, TL...>::type;

    template< tag T>
    class index_class< T> : public impl::index_base {
    public:
        index_class() noexcept
            : i_(0)
        {}
        constexpr explicit index_class(index_carrier_type< T> v) noexcept
            : i_(v)
        {}
        template< tag T2>
        index_class< T2> retag() const
        {
            return index_class< T2>(i_);
        }
        index_carrier_type<T> value() const noexcept
        {
            return i_;
        }
        template< std::size_t I>
            requires (I == 0)
        auto&& get() const noexcept
        {
            return std::get< I>(i_);
        }
        template< same_selector<T> T2>
        auto&& get() const noexcept
        {
            return *this;
        }
    private:
        index_carrier_type< T> i_;
    };

    template< tag T>
    std::ostream& operator<<(std::ostream& o, index_class<T> v)
    {
        o << v.value();
        return o;
    }

    template< tag T>
    class iterator_class< T> {
    public:
        iterator_class() noexcept
            : v_(0)
        {}
        explicit iterator_class(index_carrier_type< T> v) noexcept
            : v_(v)
        {}
        index_class< T> operator*() const noexcept
        {
            return index_class< T>(v_);
        }
        bool operator==(const iterator_class<T>& b) const noexcept
        {
            return v_ == b.v_;
        }
        bool operator!=(const iterator_class<T>& b) const noexcept
        {
            return v_ != b.v_;
        }
        iterator_class<T>& operator++() noexcept
        {
            ++v_;
            return *this;
        }
        iterator_class<T> operator++(int) noexcept
        {
            auto tmp = *this;
            operator++();
            return tmp;
        }
    private:
        index_carrier_type< T> v_;
    };

    template< non_static_tag T>
    class range_class< T> : public impl::range_base {
    public:
        using selector = tagged::selector<T>;
 
        range_class() noexcept
            : b_(0), e_(0)
        {}
        explicit range_class(index_carrier_type< T> e) noexcept
            : b_(0), e_(e)
        {}
        range_class(index_carrier_type< T> b, index_carrier_type< T> e) noexcept
            : b_(b), e_(e)
        {}
        range_class(const range_class<T>& b) = default;
        range_class<T>& operator=(const range_class<T>& b) = default;
        range_class(range_class<T>&& b) noexcept
            : b_(b.b_), e_(b.e_)
        {
            b.b_ = 0;
            b.e_ = 0;
        }
        range_class<T>& operator=(range_class<T>&& b) noexcept
        {
            b_ = b.b_;
            e_ = b.e_;
            b.b_ = 0;
            b.e_ = 0;
            return *this;
        }
        template< tag ... TL2>
            requires (sizeof...(TL2) >= 1)
        explicit range_class(const range_class< TL2...>& r) noexcept
            : b_(r.template get<selector>().begin_value()), e_(r.template get<selector>().end_value())
        {}
        template<typename T2>
            requires same_tag<T, T2>
        bool operator==(const range_class<T2>& b) const
        {
            return b_ == b.begin_value() && e_ == b.end_value();
        }
        template<typename T2>
            requires same_tag<T, T2>
        bool operator!=(const range_class<T2>& b) const
        {
            return b_ != b.begin_value() || e_ != b.end_value();
        }
        template< tag T2>
        range_class< T2> retag() const
        {
            return range_class< T2>(b_, e_);
        }
        index_carrier_type<T> flat(const index_class< selector>& i) const
        {
            return i.value() - b_;
        }
        index_carrier_type<T> size() const
        {
            return e_ - b_;
        }
        iterator_class<selector> begin() const noexcept
        {
            return iterator_class<selector>(b_);
        }
        iterator_class<selector> end() const noexcept
        {
            return iterator_class<selector>(e_);
        }
        index_carrier_type<T> begin_value() const noexcept
        {
            return b_;
        }
        index_carrier_type<T> end_value() const noexcept
        {
            return e_;
        }
        template< same_selector< T> T2>
        auto&& get() const noexcept
        {
            return *this;
        }
        template< std::size_t I>
            requires (I == 0)
        auto&& get() const noexcept
        {
            return *this;
        }
        template< std::size_t I>
            requires (I == 0)
        using get_tag = T;
    private:
        index_carrier_type< T> b_, e_;
    };

    template< static_tag T>
    class range_class< T> : public impl::range_base {
    public:
        using selector = tagged::selector<T>;
 
        constexpr range_class() noexcept
        {}
        constexpr explicit range_class(index_carrier_type< T> e) 
        {
            if (0 != T::begin || e != T::end)
            {
                throw std::logic_error("WTF");
            }
        }
        constexpr range_class(index_carrier_type< T> b, index_carrier_type< T> e) 
        {
            if (b != T::begin || e != T::end)
            {
                throw std::logic_error("WTF");
            }
        }
        template< tag ... TL2>
            requires (sizeof...(TL2) >= 1)
        explicit range_class(const range_class< TL2...>&) noexcept
            requires pick<selector, TL2...>::is_static
        {}
        template<typename T2>
        requires same_tag<T, T2>
        constexpr bool operator==(const range_class<T2>&) const
        {
            return true;
        }
        template<typename T2>
            requires same_tag<T, T2>
        constexpr bool operator!=(const range_class<T2>&) const
        {
            return false;
        }
        template< static_tag T2>
        static constexpr range_class< T2> retag()
        {
            return range_class< T2>();
        }
        static index_carrier_type<T> flat(const index_class< selector>& i)
        {
            return i.value() - T::begin;
        }
        static constexpr index_carrier_type<T> size()
        {
            return T::end - T::begin;
        }
        static iterator_class<selector> begin() noexcept
        {
            return iterator_class<selector>(T::begin);
        }
        static iterator_class<selector> end() noexcept
        {
            return iterator_class<selector>(T::end);
        }
        static constexpr index_carrier_type<T> begin_value() noexcept
        {
            return T::begin;
        }
        static constexpr index_carrier_type<T> end_value() noexcept
        {
            return T::end;
        }
        template< same_selector< T> T2>
        static constexpr auto get() noexcept
        {
            return range_class<T>{};
        }
        template< std::size_t I>
            requires (I == 0)
        auto&& get() const noexcept
        {
            return *this;
        }
        template< std::size_t I>
            requires (I == 0)
        using get_tag = T;
    };

    template< tag ... TL>
    class index_class : public impl::index_base {
    public:
        index_class() noexcept
            : i_(index_carrier_type< TL>(0) ...)
        {}
        constexpr index_class(index_carrier_type< TL> ... vl) noexcept
            : i_(index_class< TL>(vl) ...)
        {}
        index_class(index_class< TL> ... vl) noexcept
            : i_(vl ...)
        {}
        template< std::size_t I>
            requires (I < sizeof...(TL))
        auto&& get() const noexcept
        {
            return std::get< I>(i_);
        }

        template< impl::one_of< TL ...> T>
        auto&& get() const noexcept
        {
            return std::get< index_class< T>>(i_);
        }
    private:
        std::tuple< index_class< TL> ...> i_;
    };

    template<>
    class index_class<> : public impl::index_base {
    public:
        constexpr index_class() noexcept
        {}
    };

    template< tag ... TL1, tag ... TL2>
    index_class< TL1 ..., TL2 ...> operator&(const index_class< TL1 ...>& ia, const index_class< TL2 ...>& ib)
    {
        return index_class< TL1 ..., TL2 ...>(ia.template get< TL1>() ..., ib.template get< TL2>() ...);
    }

    template< tag T1, tag ... TL2>
    std::ostream& operator<<(std::ostream& o, index_class<T1, TL2 ...> v)
    {
        ((o << "[" << v.template get<T1>()), ..., (o << "," << v.template get<TL2>())), o << "]";
        return o;
    }

    template< tag ... TL>
    class iterator_class {
    public:
        iterator_class() noexcept
            : rngp_(nullptr), it_(iterator_class< TL>(0) ...)
        {}
        iterator_class(const range_class< TL...>* rngp, iterator_class< selector<TL>> ... v) noexcept
            : rngp_(rngp), it_(v ...)
        {}
        index_class< selector<TL> ...> operator*() const noexcept
        {
            return index_class< selector<TL> ...>(*std::get< iterator_class< selector< TL>>>(it_)...);
        }
        bool operator==(const iterator_class<TL ...>& b) const noexcept
        {
            return equal< sizeof...(TL)>(b);
        }
        bool operator!=(const iterator_class<TL ...>& b) const noexcept
        {
            return !equal< sizeof...(TL)>(b);
        }
        iterator_class<TL ...>& operator++() noexcept
        {
            increment< sizeof...(TL)>();
            return *this;
        }
        iterator_class<TL ...> operator++(int) noexcept
        {
            auto tmp = *this;
            operator++();
            return tmp;
        }
    private:
        template< std::size_t I>
        bool equal(const iterator_class<TL ...>& b) const noexcept
        {
            if constexpr (I > 0)
            {
                if (std::get<I - 1>(it_) != std::get<I - 1>(b.it_))
                    return false;
                return equal< I - 1>(b);
            }
            else
            {
                return true;
            }
        }
 
        template< std::size_t I>
        void increment() noexcept
        {
            auto&& iti = std::get<I - 1>(it_);
            ++iti;
            if constexpr (I > 1)
            {
                auto&& rngi = rng().template get<I - 1>();
                if (iti != rngi.end())
                    return;
                iti = rngi.begin();
                increment< I - 1>();
            }
        }
 
        const range_class< TL...>& rng() const
        {
            return *rngp_;
        }
        const range_class< TL...>* rngp_;
        std::tuple< iterator_class< selector<TL>> ...> it_;
    };

    template< tag ... TL>
    class range_class : public impl::range_base {
    public:
        range_class() noexcept
        {}
        range_class(const range_class< TL> & ... vl) noexcept requires (sizeof...(TL) > 0)
            : i_(vl ...)
        {}
        template< tag ... TL2>
        requires (sizeof...(TL2) >= sizeof...(TL))
        explicit range_class(const range_class< TL2...> & r) noexcept
            : i_(r.template get<selector<TL>>() ...)
        {}
        std::size_t size() const
        {
            return (1 * ... * get< TL>().size());
        }

        iterator_class<TL ...> begin() const noexcept
        {
            return iterator_class<TL ...>(this, get_begin< TL>() ...);
        }

        iterator_class<TL ...> end() const noexcept
        {
            return iterator_class<TL ...>(this, get_end< TL>() ...);
        }

        template< typename T>
        requires impl::one_of< selector<T>, selector<TL> ...>
        && non_static_tag< pick<selector<T>, TL ...>>
        auto&& get() const noexcept
        {
            return std::get< range_class< pick<selector<T>, TL ...>>>(i_);
        }

        template< typename T>
        requires impl::one_of< selector<T>, selector<TL> ...>
        && static_tag< pick<selector<T>, TL ...>>
        static constexpr auto get() noexcept
        {
            return range_class< pick<selector<T>, TL ...>>{};
        }

        template< std::size_t I>
        auto&& get() const noexcept
        {
            return std::get< I>(i_);
        }

        template< std::size_t I>
        using get_tag = std::tuple_element_t<I, std::tuple<TL ...>>;
    private:
        template< tag T>
        auto get_begin() const noexcept
        {
            auto&& rngi = std::get< range_class< T>>(i_);
            return rngi.begin();
        }
        template< tag T>
        auto get_end() const noexcept
        {
            auto&& rngi = std::get< range_class< T>>(i_);
            if constexpr (impl::position_of<T, TL ...> == 0)
                return rngi.end();
            else
                return rngi.begin();
        }
        using i_type = std::tuple< range_class< TL> ...>;
        i_type i_;
    };

    template< tag ... TL1, tag ... TL2>
    range_class< TL1 ..., TL2 ...> operator&(const range_class< TL1 ...>& rnga, const range_class< TL2 ...>& rngb)
    {
        return range_class< TL1 ..., TL2 ...>(rnga.template get< TL1>() ..., rngb.template get< TL2>() ...);
    }

    namespace impl {
        template< tag T>
        struct size_traits
        {
            static constexpr std::size_t static_multiplier = 1;
            static constexpr bool has_dynamic_multiplier = true;
            template< typename T2>
            static std::size_t dynamic_multiplier(T2&& r)
            {
                return r.template get<selector<T>>().size();
            }
        };
 
        template< tag T>
            requires T::is_static
        struct size_traits<T>
        {
            static constexpr std::size_t static_multiplier = T::end - T::begin;
            static constexpr bool has_dynamic_multiplier = false;
        };
 
        template< tag T>
        class multiplier_class
        {
        public:
            multiplier_class()
                : value_(0)
            {}
            explicit multiplier_class(std::size_t v)
                : value_(v)
            {}
            void assign_value(std::size_t v)
            {
                value_ = v;
            }
            std::size_t value() const
            {
                return value_;
            }
        private:
            std::size_t value_;
        };
 
        template< tag T, std::size_t s>
        struct sm_tag
        {
            static constexpr bool is_tag = true;
            static constexpr bool is_direct = false;
            using core = sm_tag< T, s>;
            static constexpr bool is_selector = false;
            using selector = T;
            template<selector_tag T2>
            using retag = sm_tag< T2, s>;
 
            static constexpr bool has_static_multiplier = true;
            static constexpr std::size_t static_multiplier = s;
        };
 
        template< tag T, std::size_t b, std::size_t e, std::size_t s>
        struct srm_tag
        {
            static constexpr bool is_tag = true;
            static constexpr bool is_direct = false;
            using core = sm_tag< T, s>;
            static constexpr bool is_selector = false;
            using selector = T;
            template<selector_tag T2>
            using retag = sm_tag< T2, s>;
 
            static constexpr bool is_static = true;
            static constexpr std::size_t begin = b;
            static constexpr std::size_t end = e;
 
            static constexpr bool has_static_multiplier = true;
            static constexpr std::size_t static_multiplier = s;
        };
 
        template< typename T>
        concept has_static_multiplier = requires {
            requires tag<T>;
            {T::has_static_multiplier} -> std::convertible_to<bool>;
            requires T::has_static_multiplier;
        };
 
        template< tag T, std::size_t s>
        class multiplier_class<sm_tag<T, s>>
        {
        public:
            multiplier_class()
            {}
            static constexpr std::size_t value()
            {
                return s;
            }
        };
 
        template< tag ... TL>
        struct multiplier_list_traits;
 
        template<>
        struct multiplier_list_traits<>
        {
            static constexpr std::size_t static_multiplier = 1;
            using multiplier_tag_list = tag_list<>;
            static constexpr bool has_dynamic_multiplier = false;
        };
 
        template< tag T0, tag ... TL>
            requires (!multiplier_list_traits< TL ...>::has_dynamic_multiplier)
            struct multiplier_list_traits< T0, TL ...>
        {
        private:
            using head_traits = size_traits<T0>;
            using tail_traits = multiplier_list_traits< TL ...>;
        public:
            static constexpr std::size_t static_multiplier = head_traits::static_multiplier * tail_traits::static_multiplier;
        private:
            using head_multiplier_tag = sm_tag<selector<T0>, tail_traits::static_multiplier>;
            using tail_multiplier_tag_list = typename tail_traits::multiplier_tag_list;
        public:
            using multiplier_tag_list = concat_list< head_multiplier_tag, tail_multiplier_tag_list>;
            static constexpr bool has_dynamic_multiplier = head_traits::has_dynamic_multiplier;
            template< tag ... TL2, tag ... TL3>
            static std::size_t fill_dynamic_multiplier(std::tuple< multiplier_class< TL2>...>&, const range_class<TL3 ...>& r)
                requires has_dynamic_multiplier
            {
                return head_traits::dynamic_multiplier(r);
            }
        };
 
        template< tag T0, tag ... TL>
            requires multiplier_list_traits< TL ...>::has_dynamic_multiplier
            struct multiplier_list_traits< T0, TL ...>
        {
        private:
            using head_traits = size_traits<T0>;
            using tail_traits = multiplier_list_traits< TL ...>;
        public:
            static constexpr std::size_t static_multiplier = head_traits::static_multiplier * tail_traits::static_multiplier;
        private:
            using head_multiplier_tag = selector<T0>;
            using tail_multiplier_tag_list = typename tail_traits::multiplier_tag_list;
        public:
            using multiplier_tag_list = concat_list< head_multiplier_tag, tail_multiplier_tag_list>;
            static constexpr bool has_dynamic_multiplier = true;
            template< tag ... TL2, tag ... TL3>
            static std::size_t fill_dynamic_multiplier(std::tuple< multiplier_class< TL2>...>& m, const range_class<TL3 ...>& r)
            {
                std::size_t dm = tail_traits::fill_dynamic_multiplier(m, r);
                std::get< multiplier_class<head_multiplier_tag>>(m).assign_value(tail_traits::static_multiplier * dm);
                if constexpr (head_traits::has_dynamic_multiplier)
                {
                    dm *= head_traits::dynamic_multiplier(r);
                }
                return dm;
            }
        };
 
        template< tag ... TL>
        class multiplier_list_class
        {
        public:
            multiplier_list_class()
            {}
            template< tag ... TL3>
                requires (sizeof...(TL3) == sizeof...(TL))
            explicit multiplier_list_class(const range_class<TL3 ...>& r)
            {
                using traits = multiplier_list_traits<pick<selector<TL>, TL3...> ...>;
                if constexpr (traits::has_dynamic_multiplier)
                {
                    traits::fill_dynamic_multiplier(m_, r);
                }
            }
            template< tag ... TL3>
                requires (sizeof...(TL3) >= sizeof...(TL))
            explicit multiplier_list_class(const multiplier_list_class<TL3 ...>& r)
                : m_( r.template get<TL>() ...)
            {}
            template< tag ... TL3, tag ... TL2>
                requires same_selector_list<tag_list<TL3...>, tag_list<TL...>>
                && subset_selector< tag_list<TL2...>, tag_list<TL...>>
            std::size_t flat(const range_class<TL3 ...>& r, const index_class<TL2 ...>& i) const
            {
                return (0 + ... + flat_one<TL2>(r, i));
            }
            template< tag T2>
            auto&& get() const
            {
                return std::get< multiplier_class<pick<selector<T2>, TL...>>>(m_);
            }
            template< std::size_t I2>
            auto&& get() const
            {
                return std::get< I2>(m_);
            }
        private:
            std::tuple< multiplier_class< TL>...> m_;
 
            template< tag T, tag ... TL3, tag ... TL2>
            std::size_t flat_one(const range_class<TL3 ...>& r, const index_class<TL2 ...>& i) const
            {
                auto&& ix = i.template get<selector<T>>();
                auto&& rx = r.template get<selector<T>>();
                    
                std::size_t mv = std::get< multiplier_class< pick<selector<T>, TL...>>>(m_).value();
                std::size_t fv = rx.flat(ix);
                return mv * fv;
            }
        };
 
        template<typename L>
        struct multiplier_list_creator;
 
        template<tag ... TL2>
        struct multiplier_list_creator< tag_list< TL2 ...>>
        {
            using type = multiplier_list_class< TL2 ...>;
        };
 
        template< tag ... TL3>
        using multiplier_list = typename multiplier_list_creator< typename multiplier_list_traits< TL3...>::multiplier_tag_list>::type;
 
        template< tag RT, tag MT>
        struct mixer_traits;
 
        template< tag RT, tag MT>
            requires same_tag<RT, selector<MT>>
        struct mixer_traits<RT, MT>
        {
            using type = MT;
        };
 
        template< tag RT, tag MT>
            requires same_tag<selector<RT>, MT>
        struct mixer_traits<RT, MT>
        {
            using type = RT;
        };
 
        template< tag RT, tag MT>
            requires RT::is_static && MT::has_static_multiplier
        struct mixer_traits<RT, MT>
        {
            using type = srm_tag<selector<RT>, RT::begin, RT::end, MT::static_multiplier>;
        };
 
        template< typename RC, typename MLC>
        struct mixer_list_traits;
 
        template<>
        struct mixer_list_traits< range_class<>, multiplier_list_class<>>
        {
            using type = tag_list<>;
        };
 
        template< tag RT, tag ... RL, tag MT, tag ... ML>
            requires (sizeof...(RL) == sizeof...(ML))
        struct mixer_list_traits< range_class< RT, RL...>, multiplier_list_class< MT, ML...>>
        {
        private:
            using head_traits = mixer_traits< RT, MT>;
            using tail_traits = mixer_list_traits< range_class< RL...>, multiplier_list_class< ML...>>;
        public:
            using type = concat_list< typename head_traits::type, typename tail_traits::type>;
        };
 
        template< tag T>
        struct range_demixer_traits
        {
            using type = selector<T>;
        };
 
        template< tag T>
            requires T::is_static
        struct range_demixer_traits<T>
        {
            using type = sr_tag<selector<T>, T::begin, T::end>;
        };
 
        template< tag T>
        struct multiplier_demixer_traits
        {
            using type = selector<T>;
        };
 
        template< tag T>
            requires T::has_static_multiplier
        struct multiplier_demixer_traits<T>
        {
            using type = sm_tag<selector<T>, T::static_multiplier>;
        };
    }
 
    template< typename E, tag ... TL>
    class tensor_class;
 
    template< typename E, tag ... TL>
    class tensor_view;
 
    namespace impl {
        template< typename E, typename X>
        struct tensor_view_creator;
 
        template< typename E, tag ... TL>
        struct tensor_view_creator< E, tag_list< TL...>>
        {
            using type = tensor_view< E, TL...>;
        };
    }

    template< typename E, tag ... TL>
    class tensor_view {
    private:
        using self_ = tensor_view< E, TL...>;
        using range_t = range_class< typename impl::range_demixer_traits< TL>::type ...>;
    public:
        template< tag ... TL3, tag ... TL2>
        explicit tensor_view(const range_class< TL3 ...>& rng, const impl::multiplier_list_class< TL2...>& mult, E* data) 
            : rng_(rng),
            mult_(mult),
            arr_(data)
        {}
 
        self_& operator=(const self_&) = delete;
        self_& operator=(self_&&) = delete;

        const range_t& range() const
        {
            return rng_;
        }

        template< tag ... TL2>
        auto operator[](const index_class< TL2 ...>& i) const
            requires (sizeof...(TL2) < sizeof...(TL))
        && impl::subset_selector< tag_list< TL2...>, tag_list< TL...>>
        {
            using result_list = typename impl::subtract_traits<tag_list< TL...>, tag_list< TL2...>>::type;
            using result_view = typename impl::tensor_view_creator< E, result_list>::type;
            return result_view(rng_, mult_, arr_ + mult_.flat(rng_, i));
        }

        template< tag ... TL2>
        E& operator[](const index_class< TL2 ...>& i) const
            requires (sizeof...(TL2) == sizeof...(TL))
        && impl::subset_selector< tag_list< TL2...>, tag_list< TL...>>
        {
            return arr_[mult_.flat(rng_, i)];
        }

        E* data() const
            requires (sizeof...(TL) == 1) && ((TL::has_static_multiplier) && ...) && ((TL::static_multiplier == 1) && ...)
        {
            return arr_;
        }

        E* flat_data() const
        {
            return arr_;
        }

        static constexpr std::size_t dimensions = sizeof...(TL);

        template< tag T2>
        std::size_t dim_size() const
        {
            return rng_.template get< selector<T2>>().size();
        }

        template< std::size_t I2>
        std::size_t dim_size() const
        {
            return rng_.template get< I2>().size();
        }

        template< tag T2>
            requires impl::has_static_multiplier< pick< selector<T2>, TL...>>
        static constexpr std::size_t dim_multiplier() 
        { 
            return pick< selector<T2>, TL...>::static_multiplier; 
        }

        template< tag T2>
            requires (!impl::has_static_multiplier< pick< selector<T2>, TL...>>)
        std::size_t dim_multiplier() const
        {
            return mult_.template get< selector<T2>>().value();
        }

        template< std::size_t I2>
            requires impl::has_static_multiplier< pick_index< I2, TL...>>
        static constexpr std::size_t dim_multiplier() 
        { 
            return pick_index< I2, TL...>::static_multiplier; 
        }

        template< std::size_t I2>
            requires (!impl::has_static_multiplier< pick_index< I2, TL...>>)
        std::size_t dim_multiplier() const
        {
            return mult_.template get< I2>().value();
        }
 
    private:
        range_t rng_;
        impl::multiplier_list_class< typename impl::multiplier_demixer_traits< TL>::type ...> mult_;
        E* arr_;
    };

    template< typename E, tag ... TL>
    using extract_tensor_view = typename impl::tensor_view_creator< E, typename impl::mixer_list_traits< range_class< TL...>, impl::multiplier_list< TL...>>::type>::type;

    template< typename E, tag ... TL>
    class tensor_class {
    public:
        tensor_class() noexcept
        {}
        template< tag ... TL2>
            requires (sizeof...(TL2) == sizeof...(TL))
        explicit tensor_class(const range_class< TL2 ...>& rng)
            : rng_(rng),
            mult_( rng),
            arr_(rng.size())
        {}

        template< tag ... TL2>
            requires (sizeof...(TL2) == sizeof...(TL))
        tensor_class(const range_class< TL2 ...>& rng, const E& e) noexcept
            : rng_(rng),
            mult_(rng),
            arr_(rng.size(), e)
        {}
 
        using view_type = extract_tensor_view< E, TL ...>;
        using const_view_type = extract_tensor_view< const E, TL ...>;

        view_type view()
        {
            return view_type(rng_, mult_, arr_.data());
        }

        const_view_type view() const
        {
            return const_view_type(rng_, mult_, arr_.data());
        }

        template< tag ... TL2>
        auto operator[](const index_class< TL2 ...>& i)
            requires (sizeof...(TL2) < sizeof...(TL))
        && impl::subset_selector< tag_list< TL2...>, tag_list< TL...>>
        {
            return view()[i];
        }

        template< tag ... TL2>
        auto operator[](const index_class< TL2 ...>& i) const
            requires (sizeof...(TL2) < sizeof...(TL))
        && impl::subset_selector< tag_list< TL2...>, tag_list< TL...>>
        {
            return view()[i];
        }

        const range_class< TL ...>& range() const
        {
            return rng_;
        }

        template< tag ... TL2>
        E& operator[](const index_class< TL2...>& i)
            requires (sizeof...(TL2) == sizeof...(TL))
        && impl::subset_selector< tag_list< TL2...>, tag_list< TL...>>
        {
            return arr_[mult_.flat(rng_, i)];
        }

        template< tag ... TL2>
        const E& operator[](const index_class< TL2...>& i) const
            requires (sizeof...(TL2) == sizeof...(TL))
        && impl::subset_selector< tag_list< TL2...>, tag_list< TL...>>
        {
            return arr_[mult_.flat(rng_, i)];
        }

        E* data()
            requires (sizeof...(TL) == 1)
        {
            return arr_.data();
        }

        const E* data() const
            requires (sizeof...(TL) == 1)
        {
            return arr_.data();
        }

        E* flat_data()
        {
            return arr_.data();
        }

        const E* flat_data() const
        {
            return arr_.data();
        }
    private:
        range_class< TL ...> rng_;
        impl::multiplier_list< TL ...> mult_;
        std::vector< E> arr_;
    };

    namespace impl {
        template< typename P, typename C>
        struct permute;
        
        template< typename ... SL, typename C>
        struct permute< tag_list< SL...>, C>
        {
            using type = typename C::template type< SL...>;
        };
 
        template< typename P, typename C>
        using permute_t = typename permute< P, C>::type;
 
        template< typename E, tag ... TL>
        struct permutator_tensor_class
        {
            template< typename ... SL>
            using type = tensor_class< E, pick<SL, TL...> ...>;
        };
 
        template< tag ... TL>
        struct permutator_range_class
        {
            template< typename ... SL>
            using type = range_class< pick<SL, TL...> ...>;
        };
 
        struct permutator_range
        {
            template< typename ... SL>
            struct type {
                template< tag ... TL>
                static auto permute_range(const range_class<TL...>& r)
                {
                    using range = range_class< pick<SL, TL...> ...>;
                    return range((r.template get<SL>() & ...));
                }
            };
        };
    }

    template< typename P, typename E, tag ... TL>
    using permute_tensor_class = impl::permute_t< P, impl::permutator_tensor_class<E, TL...>>;

    template< typename P, tag ... TL>
    using permute_range_class = impl::permute_t< P, impl::permutator_range_class<TL...>>;
 
    template< typename P, tag ... TL>
    auto permute_range(const range_class<TL...>& r)
    {
        using permutator = impl::permute_t<P, impl::permutator_range>;
        return permutator::permute_range(r);
    }
 
    // CO 

    namespace impl {
        template< selector_tag T>
        struct c {
            static constexpr bool is_tag = true;
            static constexpr bool is_direct = false;
            using core = c<T>;
            static constexpr bool is_selector = true;
            using selector = c<T>;
            template<selector_tag T2>
            using retag = T2;
        };
 
        template< selector_tag T>
        struct co_traits {
            using co = c< T>;
        };
 
        template< selector_tag T>
        struct co_traits< c<T>> {
            using co = T;
        };
    }

    template< tag T>
    using co = retag< typename impl::co_traits<selector<T>>::co, T>;

    namespace impl {
        template< typename X>
        struct co_list_traits;
            
        template< tag ... TL>
        struct co_list_traits< tag_list<TL ...>> {
            using co_list = tag_list<co<TL>...>;
        };
    }

    template< typename X>
    using co_list = typename impl::co_list_traits< X>::co_list;

    template< tag T>
    inline constexpr range_class<co<T>> operator~(const range_class<T>& r)
    {
        return range_class<co<T>>(r.template retag<co<T>>());
    }

    template< tag T>
    inline index_class<co<T>> operator~(const index_class<T>& r)
    {
        return index_class<co<T>>(r.template retag<co<T>>());
    }

 
    template< typename E, tagged::tag STL0, tagged::tag DTL0>
    inline void permute_tensor(const tagged::tensor_view< const E, STL0>& svec, const tagged::tensor_view< E, DTL0>& dvec)
    {
        auto r0 = dvec.range().template get<DTL0>();
        for (auto i0 : r0)
        {
            dvec[i0] = svec[i0];
        }
    }
 
    template< typename E, tagged::tag ... STL, tagged::tag DTL0, tagged::tag ... DTL>
    inline void permute_tensor(const tagged::tensor_view< const E, STL ...>& svec, const tagged::tensor_view< E, DTL0, DTL ...>& dvec)
    {
        auto r0 = dvec.range().template get<DTL0>();
        for (auto i0 : r0)
        {
            auto sslice = svec[i0];
            auto dslice = dvec[i0];
 
            permute_tensor(sslice, dslice);
        }
    }
 
    template< typename E, tagged::tag ... STL, tagged::tag ... DTL>
        requires (sizeof...(STL) == sizeof...(DTL))
    inline void permute_tensor(const tagged::tensor_class< E, STL ...>& svec, tagged::tensor_class< E, DTL ...>& dvec)
    {
        permute_tensor(svec.view(), dvec.view());
    }
 
}
 
#endif