/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \class QCache
    \inmodule QtCore
    \brief The QCache class is a template class that provides a cache.

    \ingroup tools
    \ingroup shared

    \reentrant

    QCache\<Key, T\> defines a cache that stores objects of type T
    associated with keys of type Key. For example, here's the
    definition of a cache that stores objects of type Employee
    associated with an integer key:

    \snippet code/doc_src_qcache.cpp 0

    Here's how to insert an object in the cache:

    \snippet code/doc_src_qcache.cpp 1

    The advantage of using QCache over some other key-based data
    structure (such as QMap or QHash) is that QCache automatically
    takes ownership of the objects that are inserted into the cache and
    deletes them to make room for new objects, if necessary. When
    inserting an object into the cache, you can specify a \e{cost},
    which should bear some approximate relationship to the amount of
    memory taken by the object. When the sum of all objects' costs
    (totalCost()) exceeds the cache's limit (maxCost()), QCache starts
    deleting objects in the cache to keep under the limit, starting with
    less recently accessed objects.

    By default, QCache's maxCost() is 100. You can specify a
    different value in the QCache constructor:

    \snippet code/doc_src_qcache.cpp 2

    Each time you call insert(), you can specify a cost as third
    argument (after the key and a pointer to the object to insert).
    After the call, the inserted object is owned by the QCache, which
    may delete it at any time to make room for other objects.

    To look up objects in the cache, use object() or
    operator[](). This function looks up an object by its key, and
    returns either a pointer to the cached object (which is owned by
    the cache) or \nullptr.

    If you want to remove an object from the cache for a particular key,
    call remove(). This will also delete the object. If you want to
    remove an object from the cache without the QCache deleting it, use
    take().

    \sa QPixmapCache, QHash, QMap
*/

/*! \fn template <class Key, class T> QCache<Key, T>::QCache(int maxCost = 100)

    Constructs a cache whose contents will never have a total cost
    greater than \a maxCost.
*/

/*! \fn template <class Key, class T> QCache<Key, T>::~QCache()

    Destroys the cache. Deletes all the objects in the cache.
*/

/*! \fn template <class Key, class T> int QCache<Key, T>::maxCost() const

    Returns the maximum allowed total cost of the cache.

    \sa setMaxCost(), totalCost()
*/

/*! \fn template <class Key, class T> void QCache<Key, T>::setMaxCost(int cost)

    Sets the maximum allowed total cost of the cache to \a cost. If
    the current total cost is greater than \a cost, some objects are
    deleted immediately.

    \sa maxCost(), totalCost()
*/

/*! \fn template <class Key, class T> int QCache<Key, T>::totalCost() const

    Returns the total cost of the objects in the cache.

    This value is normally below maxCost(), but QCache makes an
    exception for Qt's \l{implicitly shared} classes. If a cached
    object shares its internal data with another instance, QCache may
    keep the object lying around, possibly contributing to making
    totalCost() larger than maxCost().

    \sa setMaxCost()
*/

/*! \fn template <class Key, class T> int QCache<Key, T>::size() const

    Returns the number of objects in the cache.

    \sa isEmpty()
*/

/*! \fn template <class Key, class T> int QCache<Key, T>::count() const

    Same as size().
*/

/*! \fn template <class Key, class T> bool QCache<Key, T>::isEmpty() const

    Returns \c true if the cache contains no objects; otherwise
    returns \c false.

    \sa size()
*/

/*! \fn template <class Key, class T> QList<Key> QCache<Key, T>::keys() const

    Returns a list of the keys in the cache.
*/

/*! \fn template <class Key, class T> void QCache<Key, T>::clear();

    Deletes all the objects in the cache.

    \sa remove(), take()
*/


/*! \fn template <class Key, class T> bool QCache<Key, T>::insert(const Key &key, T *object, int cost = 1)

    Inserts \a object into the cache with key \a key and
    associated cost \a cost. Any object with the same key already in
    the cache will be removed.

    After this call, \a object is owned by the QCache and may be
    deleted at any time. In particular, if \a cost is greater than
    maxCost(), the object will be deleted immediately.

    The function returns \c true if the object was inserted into the
    cache; otherwise it returns \c false.

    \sa take(), remove()
*/

/*! \fn template <class Key, class T> T *QCache<Key, T>::object(const Key &key) const

    Returns the object associated with key \a key, or \nullptr if the key does
    not exist in the cache.

    \warning The returned object is owned by QCache and may be
    deleted at any time.

    \sa take(), remove()
*/

/*! \fn template <class Key, class T> bool QCache<Key, T>::contains(const Key &key) const

    Returns \c true if the cache contains an object associated with key \a
    key; otherwise returns \c false.

    \sa take(), remove()
*/

/*! \fn template <class Key, class T> T *QCache<Key, T>::operator[](const Key &key) const

    Returns the object associated with key \a key, or \nullptr if the key does
    not exist in the cache.

    This is the same as object().

    \warning The returned object is owned by QCache and may be
    deleted at any time.
*/

/*! \fn template <class Key, class T> bool QCache<Key, T>::remove(const Key &key)

    Deletes the object associated with key \a key. Returns \c true if the
    object was found in the cache; otherwise returns \c false.

    \sa take(), clear()
*/

/*! \fn template <class Key, class T> T *QCache<Key, T>::take(const Key &key)

    Takes the object associated with key \a key out of the cache
    without deleting it. Returns a pointer to the object taken out, or
    0 if the key does not exist in the cache.

    The ownership of the returned object is passed to the caller.

    \sa remove()
*/