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

    #include "../interfaces/enumerable.h"
    #include "../interfaces/remover.h"
    #include "../serialize.h"
    #include "../algs.h"
    #include <functional>

    namespace dlib
    {

        template <
            typename T,
            typename mem_manager = default_memory_manager,
            typename compare = std::less<T>
            >
        class set : public enumerable<const T>,
                    public asc_remover<T,compare>
        {

            /*!
                REQUIREMENTS ON T
                    T must be comparable by compare where compare is a functor compatible with std::less and
                    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 is_member() functions do not invalidate pointers
                    or references to internal data.
                    All other functions have no such guarantee.

                INITIAL VALUE
                    size() == 0

                ENUMERATION ORDER
                    The enumerator will iterate over the elements in the set in
                    ascending order according to the compare functor.
                    (i.e. the elements are enumerated in sorted order)

                WHAT THIS OBJECT REPRESENTS
                    set contains items of type T

                    This object represents an unaddressed collection of items.
                    Every element in a set is unique.

                    definition of equivalent:
                    a is equivalent to b if
                    a < b == false and
                    b < a == false
            !*/

            public:

                typedef T type;
                typedef compare compare_type;
                typedef mem_manager mem_manager_type;

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

                virtual ~set(
                );
                /*!
                    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 (
                    T& item
                );
                /*!
                    requires
                        - is_member(item) == false
                    ensures
                        - #is_member(item) == true
                        - #item has an initial value for its type
                        - #size() == size() + 1
                        - #at_start() == true
                    throws
                        - std::bad_alloc or any exception thrown by T's constructor
                            if add() throws then it has no effect
                !*/

                bool is_member (
                    const T& item
                ) const;
                /*!
                    ensures
                        - returns whether or not there is an element in *this equivalent to
                          item
                !*/

                void remove (
                    const T& item,
                    T& item_copy
                );
                /*!
                    requires
                        - is_member(item) == true
                        - &item != &item_copy (i.e. item and item_copy cannot be the same
                          variable)
                    ensures
                        - #is_member(item) == false
                        - the element in *this equivalent to item has been removed and
                          swapped into #item_copy
                        - #size() == size() - 1
                        - #at_start() == true
                !*/

                void destroy (
                    const T& item
                );
                /*!
                    requires
                        - is_member(item) == true
                    ensures
                        - #is_member(item) == false
                        - #size() == size() - 1
                        - #at_start() == true
                !*/

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

            private:

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

        };

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

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

    #endif // DLIB_SET_KERNEl_ABSTRACT_