    // Copyright (C) 2006  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_MEMORY_MANAGER_STATELESs_ABSTRACT_
    #ifdef DLIB_MEMORY_MANAGER_STATELESs_ABSTRACT_

    #include "../algs.h"
    #include <memory>

    namespace dlib
    {
        template <
            typename T
            >
        class memory_manager_stateless
        {
            /*!
                REQUIREMENTS ON T
                    T must have a default constructor.

                WHAT THIS OBJECT REPRESENTS
                    This object represents some kind of stateless memory manager or memory pool.
                    Stateless means that all instances (instances of the same kernel implementation that is)
                    of this object are identical and can be used interchangeably.  Note that
                    implementations are allowed to have some shared global state such as a
                    global memory pool.

                THREAD SAFETY
                    This object is thread safe.  You may access it from any thread at any time
                    without synchronizing access.
            !*/

            public:

                typedef T type;
                const static bool is_stateless = true;

                template <typename U>
                struct rebind {
                    typedef memory_manager_stateless<U> other;
                };

                memory_manager_stateless(
                );
                /*!
                    ensures
                        - #*this is properly initialized
                    throws
                        - std::bad_alloc
                !*/

                virtual ~memory_manager_stateless(
                );
                /*!
                    ensures
                        - frees any resources used by *this but has no effect on any shared global
                          resources used by the implementation.
                !*/

                T* allocate (
                );
                /*!
                    ensures
                        - allocates a new object of type T and returns a pointer to it.
                    throws
                        - std::bad_alloc or any exception thrown by T's constructor.
                            If this exception is thrown then the call to allocate()
                            has no effect on #*this.
                !*/

                void deallocate (
                    T* item
                );
                /*!
                    requires
                        - item == is a pointer to memory that was obtained from a call to
                          allocate(). (i.e. The pointer you are deallocating must have
                          come from the same implementation of memory_manager_stateless
                          that is trying to deallocate it.)
                        - the memory pointed to by item hasn't already been deallocated.
                    ensures
                        - deallocates the object pointed to by item
                !*/

                T* allocate_array (
                    size_t size
                );
                /*!
                    ensures
                        - allocates a new array of size objects of type T and returns a
                          pointer to it.
                    throws
                        - std::bad_alloc or any exception thrown by T's constructor.
                            If this exception is thrown then the call to allocate()
                            has no effect on #*this.
                !*/

                void deallocate_array (
                    T* item
                );
                /*!
                    requires
                        - item == is a pointer to memory that was obtained from a call to
                          allocate_array(). (i.e. The pointer you are deallocating must have
                          come from the same implementation of memory_manager_stateless
                          that is trying to deallocate it.)
                        - the memory pointed to by item hasn't already been deallocated.
                    ensures
                        - deallocates the array pointed to by item
                !*/

                void swap (
                    memory_manager_stateless& item
                );
                /*!
                    ensures
                        - this function has no effect on *this or item.  It is just provided
                          to make this object's interface more compatible with the other
                          memory managers.
                !*/

                std::unique_ptr<T> extract(
                    T* item
                );
                /*!
                    requires
                        - item == is a pointer to memory that was obtained from a call to
                          allocate().
                    ensures
                        - returns a unique_ptr that owns item.  That is, if the returned ptr is
                          PTR then PTR.get() == item.  Therefore, this function extracts item
                          from the memory manager's internal pool.  Therefore, you shouldn't
                          call deallocate(item) after this.
                        - Note that not all memory managers implement extract().
                !*/

                std::unique_ptr<T[]> extract_array(
                    T* item
                );
                /*!
                    requires
                        - item == is a pointer to memory that was obtained from a call to
                          allocate_array().
                    ensures
                        - returns a unique_ptr that owns item.  That is, if the returned ptr is
                          PTR then PTR.get() == item.  Therefore, this function extracts item
                          from the memory manager's internal pool.  Therefore, you shouldn't
                          call deallocate_array(item) after this.
                        - Note that not all memory managers implement extract().
                !*/

            private:

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

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

    }

    #endif // DLIB_MEMORY_MANAGER_STATELESs_ABSTRACT_