.. SPDX-FileCopyrightText: 2019-2020 Intel Corporation
..
.. SPDX-License-Identifier: CC-BY-4.0

===========================
accessor and const_accessor
===========================

Member classes ``concurrent_hash_map::accessor`` and ``concurrent_hash_map::const_accessor`` are called `accessors`.
Accessors allow multiple threads to concurrently access the key-value pairs in ``concurrent_hash_map``.
An accessor is called `empty` if it does not point to any item.

``accessor`` member class
-------------------------

Member class ``concurrent_hash_map::accessor`` provides read-write access to the key-value pair in ``concurrent_hash_map``.

.. code:: cpp

    namespace tbb {

        template <typename Key, typename T, typename HashCompare, typename Allocator>
        class concurrent_hash_map<Key, T, HashCompare, Allocator>::accessor {
            using value_type = std::pair<const Key, T>;

            accessor();
            ~accessor();

            bool empty() const;
            value_type& operator*() const;
            value_type* operator->() const;

            void release();
        }; // class accessor

    } // namespace tbb

``const_accessor`` member class
-------------------------------

Member class ``concurrent_hash_map::const_accessor`` provides read only access to the key-value pair in ``concurrent_hash_map``.

.. code:: cpp

    namespace tbb {

        template <typename Key, typename T, typename HashCompare, typename Allocator>
        class concurrent_hash_map<Key, T, HashCompare, Allocator>::const_accessor {
            using value_type = const std::pair<const Key, T>;

            const_accessor();
            ~const_accessor();

            bool empty() const;
            value_type& operator*() const;
            value_type* operator->() const;

            void release();
        }; // class const_accessor

    } // namespace tbb

Member functions
----------------

Construction and destruction
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    .. code:: cpp

        accessor();

        const_accessor();

    Constructs an empty accessor.

--------------------------

    .. code:: cpp

        ~accessor();

        ~const_accessor();

    Destroys the accessor. If ``*this`` is not empty, releases the ownership of the element.

Emptiness
~~~~~~~~~

    .. code:: cpp

        bool empty() const;

    **Returns**: ``true`` if the accessor is empty; ``false``, otherwise.

Key-value pair access
~~~~~~~~~~~~~~~~~~~~~

    .. code:: cpp

        value_type& operator*() const;

    **Returns**: a reference to the key-value pair to which the accessor points.

    The behavior is undefined if the accessor is empty.

--------------------------

    .. code:: cpp

        value_type* operator->() const;

    **Returns**: a pointer to the key-value pair to which the accessor points.

    The behavior is undefined if the accessor is empty.

Releasing
~~~~~~~~~

    .. code:: cpp

        void release();

    If ``*this`` is not empty, releases the ownership of the element. ``*this`` becomes empty.