    // Copyright (C) 2003  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_SEQUENCE_KERNEl_ABSTRACT_
    #ifdef DLIB_SEQUENCE_KERNEl_ABSTRACT_

    #include "../interfaces/enumerable.h"
    #include "../interfaces/remover.h"
    #include "../serialize.h"
    #include "../algs.h"

    namespace dlib
    {
        template <
            typename T,
            typename mem_manager = default_memory_manager
            >
        class sequence : public enumerable<T>,
                         public remover<T>
        {

            /*!
                REQUIREMENTS ON T
                    T must be swappable by a global swap() and
                    T must have a default constructor

                REQUIREMENTS ON mem_manager
                    must be an implementation of memory_manager/memory_manager_kernel_abstract.h or
                    must be an implementation of memory_manager_global/memory_manager_global_kernel_abstract.h or
                    must be an implementation of memory_manager_stateless/memory_manager_stateless_kernel_abstract.h
                    mem_manager::type can be set to anything.

                POINTERS AND REFERENCES TO INTERNAL DATA
                    swap() and operator[] functions do not invalidate pointers or
                    references to internal data.
                    All other functions have no such guarantees.

                ENUMERATION ORDER
                    The enumerator will iterate over the elements in the sequence from
                    the 0th element to the (size()-1)th element.

                INITIAL VALUE
                    size() == 0

                WHAT THIS OBJECT REPRESENTS
                    sequence contains items of type T

                    This object represents an ordered sequence of items, each item is
                    associated with an integer value.
                    The items are numbered from 0 to size()-1

                    Also note that unless specified otherwise, no member functions
                    of this object throw exceptions.
            !*/

            public:

                typedef T type;
                typedef mem_manager mem_manager_type;

                sequence (
                );
                /*!
                    ensures
                        - #*this is properly initialized
                    throws
                        - std::bad_alloc or any exception thrown by T's constructor
                !*/

                virtual ~sequence (
                );
                /*!
                    ensures
                        - all memory associated with *this has been released
                !*/

                void clear (
                );
                /*!
                    ensures
                        - #*this has its initial value
                    throws
                        - std::bad_alloc or any exception thrown by T's constructor
                            if this exception is thrown then *this is unusable
                            until clear() is called and succeeds
                !*/

                void add (
                    unsigned long pos,
                    T& item
                );
                /*!
                    requires
                        - pos <= size()
                    ensures
                        - #size() == size() + 1
                        - #item has an initial value for its type
                        - #operator[](pos) == item
                          i.e. item has been inserted into *this between the elements which
                          were previously at position pos-1 and pos
                        - #at_start() == true
                    throws
                        - std::bad_alloc or any exception thrown by T's constructor
                            if add() throws then it has no effect
                !*/

                void remove (
                    unsigned long pos,
                    T& item
                );
                /*!
                    requires
                        - pos < size()
                    ensures
                        - #size() == size() - 1
                        - the element at the position pos in *this has been removed and
                          swapped into #item
                        - #at_start() == true
                !*/

                void cat (
                    sequence& item
                );
                /*!
                    requires
                        - &item != this  (i.e. you can't concatenate a sequence onto itself)
                    ensures
                        - item has been concatenated onto the end of *this
                          i.e. item[0] becomes (#*this)[size()], item[1]
                          becomes (#*this)[size()+1], etc.
                        - #size() == size() + item.size()
                        - #item has its initial value
                        - #at_start() == true
                !*/

                const T& operator[] (
                    unsigned long pos
                ) const;
                /*!
                    requires
                        - pos < size()
                    ensures
                        - returns a const reference to the element at position pos
                !*/

                T& operator[] (
                    unsigned long pos
                );
                /*!
                    requires
                        - pos < size()
                    ensures
                        - returns a non-const reference to the element at position pos
                !*/

                void swap (
                    sequence& item
                );
                /*!
                    ensures
                        - swaps *this and item
                !*/

            private:

                // restricted functions
                sequence(sequence&);        // copy constructor
                sequence& operator=(sequence&);    // assignment operator

        };

        template <
            typename T,
            typename mem_manager
            >
        inline void swap (
            sequence<T,mem_manager>& a,
            sequence<T,mem_manager>& b
        ) { a.swap(b); }
        /*!
            provides a global swap function
        !*/

        template <
            typename T,
            typename mem_manager
            >
        void deserialize (
            sequence<T,mem_manager>& item,
            std::istream& in
        );
        /*!
            provides deserialization support
        !*/
    }

    #endif // DLIB_SEQUENCE_KERNEl_ABSTRACT_