Long Live QMap as a refcounted std::map!

... and QMultiMap as std::multimap.

Just use the implementation from the STL; we can't really claim that
our code is much better than STL's, or does things any differently
(de facto they're both red-black trees).

Decouple QMultiMap from QMap, by making it NOT inherit from
QMap any longer. This completes the deprecation started in 5.15:
QMap now does not store duplicated keys any more.

Something to establish is where to put the
QExplictlySharedDataPointer replcement that is in there as an
ad-hoc solution. There's a number of patches in-flight by Marc
that try to introduce the same (or very similar) functionality.

Miscellanea changes to the Q(Multi)Map code itself:

* consistently use size_type instead of int;
* pass iterators by value;
* drop QT_STRICT_ITERATORS;
* iterators implictly convert to const_iterators, and APIs
  take const_iterators;
* iterators are just bidirectional and not random access;
* added noexcept where it makes sense;
* "inline" dropped (churn);
* qMapLessThanKey dropped (undocumented, 0 hits in Qt, 1 hit in KDE);
* operator== on Q(Multi)Map requires operator== on the key type
  (we're checking for equality, not equivalence!).

Very few breakages occur in qtbase.

[ChangeLog][Potentially Source-Incompatible Changes] QMap does not
support multiple equivalent keys any more. Any related functionality
has been removed from QMap, following the deprecation that happened
in Qt 5.15. Use QMultiMap for this use case.

[ChangeLog][Potentially Source-Incompatible Changes] QMap and
QMultiMap iterators random-access API have been removed. Note that
the iterators have always been just bidirectional; moving
an iterator by N positions can still be achieved using std::next
or std::advance, at the same cost as before (O(N)).

[ChangeLog][Potentially Source-Incompatible Changes] QMultiMap does
not inherit from QMap any more. Amongst other things, this means
that iterators on a QMultiMap now belong to the QMultiMap class
(and not to the QMap class); new Java iterators have been added.

Change-Id: I5a0fe9b020f92c21b37065a1defff783b5d2b7a9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 1371 insertions, 0 deletions

diff --git a/src/corelib/tools/qmap.qdoc b/src/corelib/tools/qmap.qdoc
new file mode 100644
index 0000000000..09798620b7
--- /dev/null
+++ b/src/corelib/tools/qmap.qdoc
@@ -0,0 +1,1371 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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 Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+    \class QMap
+    \inmodule QtCore
+    \brief The QMap class is a template class that provides an associative array.
+
+    \ingroup tools
+    \ingroup shared
+
+    \reentrant
+
+    QMap\<Key, T\> is one of Qt's generic \l{container classes}. It
+    stores (key, value) pairs and provides fast lookup of the
+    value associated with a key.
+
+    QMap and QHash provide very similar functionality. The
+    differences are:
+
+    \list
+    \li QHash provides average faster lookups than QMap. (See \l{Algorithmic
+       Complexity} for details.)
+    \li When iterating over a QHash, the items are arbitrarily ordered.
+       With QMap, the items are always sorted by key.
+    \li The key type of a QHash must provide operator==() and a global
+       qHash(Key) function. The key type of a QMap must provide
+       operator<() specifying a total order. Since Qt 5.8.1 it is also safe
+       to use a pointer type as key, even if the underlying operator<()
+       does not provide a total order.
+    \endlist
+
+    Here's an example QMap with QString keys and \c int values:
+    \snippet code/src_corelib_tools_qmap.cpp 0
+
+    To insert a (key, value) pair into the map, you can use operator[]():
+
+    \snippet code/src_corelib_tools_qmap.cpp 1
+
+    This inserts the following three (key, value) pairs into the
+    QMap: ("one", 1), ("three", 3), and ("seven", 7). Another way to
+    insert items into the map is to use insert():
+
+    \snippet code/src_corelib_tools_qmap.cpp 2
+
+    To look up a value, use operator[]() or value():
+
+    \snippet code/src_corelib_tools_qmap.cpp 3
+
+    If there is no item with the specified key in the map, these
+    functions return a \l{default-constructed value}.
+
+    If you want to check whether the map contains a certain key, use
+    contains():
+
+    \snippet code/src_corelib_tools_qmap.cpp 4
+
+    There is also a value() overload that uses its second argument as
+    a default value if there is no item with the specified key:
+
+    \snippet code/src_corelib_tools_qmap.cpp 5
+
+    In general, we recommend that you use contains() and value()
+    rather than operator[]() for looking up a key in a map. The
+    reason is that operator[]() silently inserts an item into the
+    map if no item exists with the same key (unless the map is
+    const). For example, the following code snippet will create 1000
+    items in memory:
+
+    \snippet code/src_corelib_tools_qmap.cpp 6
+
+    To avoid this problem, replace \c map[i] with \c map.value(i)
+    in the code above.
+
+    If you want to navigate through all the (key, value) pairs stored
+    in a QMap, you can use an iterator. QMap provides both
+    \l{Java-style iterators} (QMapIterator and QMutableMapIterator)
+    and \l{STL-style iterators} (QMap::const_iterator and
+    QMap::iterator). Here's how to iterate over a QMap<QString, int>
+    using a Java-style iterator:
+
+    \snippet code/src_corelib_tools_qmap.cpp 7
+
+    Here's the same code, but using an STL-style iterator this time:
+
+    \snippet code/src_corelib_tools_qmap.cpp 8
+
+    The items are traversed in ascending key order.
+
+    Normally, a QMap allows only one value per key. If you call
+    insert() with a key that already exists in the QMap, the
+    previous value will be erased. For example:
+
+    \snippet code/src_corelib_tools_qmap.cpp 9
+
+    However, you can store multiple values per key by using
+    QMultiMap. If you want
+    to retrieve all the values for a single key, you can use
+    values(const Key &key), which returns a QList<T>:
+
+    \snippet code/src_corelib_tools_qmap.cpp 10
+
+    Another approach is to call
+    find() to get the STL-style iterator for the first item with a
+    key and iterate from there:
+
+    \snippet code/src_corelib_tools_qmap.cpp 11
+
+    If you only need to extract the values from a map (not the keys),
+    you can also use \l{foreach}:
+
+    \snippet code/src_corelib_tools_qmap.cpp 12
+
+    Items can be removed from the map in several ways. One way is to
+    call remove(); this will remove any item with the given key.
+    Another way is to use QMutableMapIterator::remove(). In addition,
+    you can clear the entire map using clear().
+
+    QMap's key and value data types must be \l{assignable data
+    types}. This covers most data types you are likely to encounter,
+    but the compiler won't let you, for example, store a QWidget as a
+    value; instead, store a QWidget *. In addition, QMap's key type
+    must provide operator<(). QMap uses it to keep its items sorted,
+    and assumes that two keys \c x and \c y are equivalent if neither \c{x
+    < y} nor \c{y < x} is true.
+
+    Example:
+    \snippet code/src_corelib_tools_qmap.cpp 13
+
+    In the example, we start by comparing the employees' names. If
+    they're equal, we compare their dates of birth to break the tie.
+
+    \sa QMapIterator, QMutableMapIterator, QHash, QSet
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::QMap()
+
+    Constructs an empty map.
+
+    \sa clear()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::QMap(const QMap<Key, T> &other)
+
+    Constructs a copy of \a other.
+
+    This operation occurs in \l{constant time}, because QMap is
+    \l{implicitly shared}. This makes returning a QMap from a
+    function very fast. If a shared instance is modified, it will be
+    copied (copy-on-write), and this takes \l{linear time}.
+
+    \sa operator=
+*/
+
+/*!
+    \fn template <class Key, class T> QMap<Key, T>::QMap(QMap<Key, T> &&other)
+
+    Move-constructs a QMap instance.
+
+    \since 5.2
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T> &QMap<Key, T>::operator=(const QMap<Key, T> &other)
+
+    Assigns \a other to this map and returns a reference to this map.
+*/
+
+/*!
+    \fn template <class Key, class T> QMap<Key, T> &QMap<Key, T>::operator=(QMap<Key, T> &&other)
+
+    Move-assigns \a other to this QMap instance.
+
+    \since 5.2
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::~QMap()
+
+    Destroys the map. References to the values in the map, and all
+    iterators over this map, become invalid.
+*/
+
+/*! \fn template <class Key, class T> void QMap<Key, T>::swap(QMap<Key, T> &other) noexcept
+    \since 4.8
+
+    Swaps map \a other with this map. This operation is very
+    fast and never fails.
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::QMap(std::initializer_list<std::pair<Key,T> > list)
+    \since 5.1
+
+    Constructs a map with a copy of each of the elements in the
+    initializer list \a list.
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::QMap(const std::map<Key, T> & other)
+
+    Constructs a copy of \a other.
+
+    \sa toStdMap()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::QMap(std::map<Key, T> && other)
+
+    Constructs a map by moving from \a other.
+
+    \sa toStdMap()
+*/
+
+/*! \fn template <class Key, class T> std::map<Key, T> QMap<Key, T>::toStdMap() const
+
+    Returns an STL map equivalent to this QMap.
+*/
+
+/*! \fn template <class Key, class T> bool operator==(const QMap<Key, T> &lhs, const QMap<Key, T> &rhs) const
+    \relates QMap
+
+    Returns \c true if \a lhs is equal to \a rhs; otherwise returns
+    false.
+
+    Two maps are considered equal if they contain the same (key,
+    value) pairs.
+
+    This function requires the key and the value types to implement \c
+    operator==().
+
+    \sa operator!=()
+*/
+
+/*! \fn template <class Key, class T> bool operator!=(const QMap<Key, T> &lhs, const QMap<Key, T> &rhs) const
+    \relates QMap
+
+    Returns \c true if \a lhs is not equal to \a rhs; otherwise returns
+    false.
+
+    Two maps are considered equal if they contain the same (key,
+    value) pairs.
+
+    This function requires the key and the value types to implement \c
+    operator==().
+
+    \sa operator==()
+*/
+
+/*! \fn template <class Key, class T> size_type QMap<Key, T>::size() const
+
+    Returns the number of (key, value) pairs in the map.
+
+    \sa isEmpty(), count()
+*/
+
+/*!
+    \fn template <class Key, class T> bool QMap<Key, T>::isEmpty() const
+
+    Returns \c true if the map contains no items; otherwise returns
+    false.
+
+    \sa size()
+*/
+
+/*! \fn template <class Key, class T> void QMap<Key, T>::detach()
+
+    \internal
+
+    Detaches this map from any other maps with which it may share
+    data.
+
+    \sa isDetached()
+*/
+
+/*! \fn template <class Key, class T> bool QMap<Key, T>::isDetached() const
+
+    \internal
+
+    Returns \c true if the map's internal data isn't shared with any
+    other map object; otherwise returns \c false.
+
+    \sa detach()
+*/
+
+/*! \fn template <class Key, class T> bool QMap<Key, T>::isSharedWith(const QMap<Key, T> &other) const
+
+    \internal
+*/
+
+/*! \fn template <class Key, class T> void QMap<Key, T>::clear()
+
+    Removes all items from the map.
+
+    \sa remove()
+*/
+
+/*! \fn template <class Key, class T> size_type QMap<Key, T>::remove(const Key &key)
+
+    Removes all the items that have the key \a key from the map.
+    Returns the number of items removed which will be 1 if the key
+    exists in the map, and 0 otherwise.
+
+    \sa clear(), take()
+*/
+
+/*! \fn template <class Key, class T> T QMap<Key, T>::take(const Key &key)
+
+    Removes the item with the key \a key from the map and returns
+    the value associated with it.
+
+    If the item does not exist in the map, the function simply
+    returns a \l{default-constructed value}. If there are multiple
+    items for \a key in the map, only the most recently inserted one
+    is removed and returned.
+
+    If you don't use the return value, remove() is more efficient.
+
+    \sa remove()
+*/
+
+/*! \fn template <class Key, class T> bool QMap<Key, T>::contains(const Key &key) const
+
+    Returns \c true if the map contains an item with key \a key;
+    otherwise returns \c false.
+
+    \sa count()
+*/
+
+/*!
+    \fn template <class Key, class T> Key QMap<Key, T>::key(const T &value, const Key &defaultKey) const
+    \since 4.3
+    \overload
+
+    Returns the first key with value \a value, or \a defaultKey if
+    the map contains no item with value \a value. If no \a defaultKey
+    is provided the function returns a
+    \l{default-constructed value}{default-constructed key}.
+
+    This function can be slow (\l{linear time}), because QMap's
+    internal data structure is optimized for fast lookup by key, not
+    by value.
+
+    \sa value(), keys()
+*/
+
+/*! \fn template <class Key, class T> T QMap<Key, T>::value(const Key &key, const T &defaultValue) const
+
+    Returns the value associated with the key \a key.
+
+    If the map contains no item with key \a key, the function returns
+    \a defaultValue. If no \a defaultValue is specified, the function
+    returns a \l{default-constructed value}.
+
+    \sa key(), values(), contains(), operator[]()
+*/
+
+/*! \fn template <class Key, class T> T &QMap<Key, T>::operator[](const Key &key)
+
+    Returns the value associated with the key \a key as a modifiable
+    reference.
+
+    If the map contains no item with key \a key, the function inserts
+    a \l{default-constructed value} into the map with key \a key, and
+    returns a reference to it. If the map contains multiple items
+    with key \a key, this function returns a reference to the most
+    recently inserted value.
+
+    \sa insert(), value()
+*/
+
+/*! \fn template <class Key, class T> T QMap<Key, T>::operator[](const Key &key) const
+
+    \overload
+
+    Same as value().
+*/
+
+/*! \fn template <class Key, class T> QList<Key> QMap<Key, T>::keys() const
+
+    Returns a list containing all the keys in the map in ascending
+    order.
+
+    The order is guaranteed to be the same as that used by values().
+
+    This function creates a new list, in \l {linear time}. The time and memory
+    use that entails can be avoided by iterating from \l keyBegin() to
+    \l keyEnd().
+
+    \sa QMultiMap::uniqueKeys(), values(), key()
+*/
+
+/*! \fn template <class Key, class T> QList<Key> QMap<Key, T>::keys(const T &value) const
+
+    \overload
+
+    Returns a list containing all the keys associated with value \a
+    value in ascending order.
+
+    This function can be slow (\l{linear time}), because QMap's
+    internal data structure is optimized for fast lookup by key, not
+    by value.
+*/
+
+/*! \fn template <class Key, class T> QList<T> QMap<Key, T>::values() const
+
+    Returns a list containing all the values in the map, in ascending
+    order of their keys. If a key is associated with multiple values,
+    all of its values will be in the list, and not just the most
+    recently inserted one.
+
+    This function creates a new list, in \l {linear time}. The time and memory
+    use that entails can be avoided by iterating from \l keyValueBegin() to
+    \l keyValueEnd().
+
+    \sa keys(), value()
+*/
+
+/*! \fn template <class Key, class T> size_type QMap<Key, T>::count(const Key &key) const
+
+    Returns the number of items associated with key \a key.
+
+    \sa contains()
+*/
+
+/*! \fn template <class Key, class T> size_type QMap<Key, T>::count() const
+
+    \overload
+
+    Same as size().
+*/
+
+/*! \fn template <class Key, class T> const Key &QMap<Key, T>::firstKey() const
+    \since 5.2
+
+    Returns a reference to the smallest key in the map.
+    This function assumes that the map is not empty.
+
+    This executes in \l{constant time}.
+
+    \sa lastKey(), first(), keyBegin(), isEmpty()
+*/
+
+/*! \fn template <class Key, class T> const Key &QMap<Key, T>::lastKey() const
+    \since 5.2
+
+    Returns a reference to the largest key in the map.
+    This function assumes that the map is not empty.
+
+    This executes in \l{logarithmic time}.
+
+    \sa firstKey(), last(), keyEnd(), isEmpty()
+*/
+
+/*! \fn template <class Key, class T> T &QMap<Key, T>::first()
+    \since 5.2
+
+    Returns a reference to the first value in the map, that is the value mapped
+    to the smallest key. This function assumes that the map is not empty.
+
+    When unshared (or const version is called), this executes in \l{constant time}.
+
+    \sa last(), firstKey(), isEmpty()
+*/
+
+/*! \fn template <class Key, class T> const T &QMap<Key, T>::first() const
+    \since 5.2
+
+    \overload
+*/
+
+/*! \fn template <class Key, class T> T &QMap<Key, T>::last()
+    \since 5.2
+
+    Returns a reference to the last value in the map, that is the value mapped
+    to the largest key. This function assumes that the map is not empty.
+
+    When unshared (or const version is called), this executes in \l{logarithmic time}.
+
+    \sa first(), lastKey(), isEmpty()
+*/
+
+/*! \fn template <class Key, class T> const T &QMap<Key, T>::last() const
+    \since 5.2
+
+    \overload
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::begin()
+
+    Returns an \l{STL-style iterators}{STL-style iterator} pointing to the first item in
+    the map.
+
+    \sa constBegin(), end()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::begin() const
+
+    \overload
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::cbegin() const
+    \since 5.0
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first item
+    in the map.
+
+    \sa begin(), cend()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::constBegin() const
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first item
+    in the map.
+
+    \sa begin(), constEnd()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::key_iterator QMap<Key, T>::keyBegin() const
+    \since 5.6
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first key
+    in the map.
+
+    \sa keyEnd(), firstKey()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::end()
+
+    Returns an \l{STL-style iterators}{STL-style iterator} pointing to the imaginary item
+    after the last item in the map.
+
+    \sa begin(), constEnd()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::end() const
+
+    \overload
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::cend() const
+    \since 5.0
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary
+    item after the last item in the map.
+
+    \sa cbegin(), end()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::constEnd() const
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary
+    item after the last item in the map.
+
+    \sa constBegin(), end()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::key_iterator QMap<Key, T>::keyEnd() const
+    \since 5.6
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary
+    item after the last key in the map.
+
+    \sa keyBegin(), lastKey()
+*/
+
+
+/*! \fn template <class Key, class T> QMap<Key, T>::key_value_iterator QMap<Key, T>::keyValueBegin()
+    \since 5.10
+
+    Returns an \l{STL-style iterators}{STL-style iterator} pointing to the first entry
+    in the map.
+
+    \sa keyValueEnd()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::key_value_iterator QMap<Key, T>::keyValueEnd()
+    \since 5.10
+
+    Returns an \l{STL-style iterators}{STL-style iterator} pointing to the imaginary
+    entry after the last entry in the map.
+
+    \sa keyValueBegin()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_key_value_iterator QMap<Key, T>::keyValueBegin() const
+    \since 5.10
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first entry
+    in the map.
+
+    \sa keyValueEnd()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_key_value_iterator QMap<Key, T>::constKeyValueBegin() const
+    \since 5.10
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first entry
+    in the map.
+
+    \sa keyValueBegin()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_key_value_iterator QMap<Key, T>::keyValueEnd() const
+    \since 5.10
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary
+    entry after the last entry in the map.
+
+    \sa keyValueBegin()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_key_value_iterator QMap<Key, T>::constKeyValueEnd() const
+    \since 5.10
+
+    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary
+    entry after the last entry in the map.
+
+    \sa constKeyValueBegin()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::erase(const_iterator pos)
+
+    Removes the (key, value) pair pointed to by the iterator \a pos
+    from the map, and returns an iterator to the next item in the
+    map.
+
+    \sa remove()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::find(const Key &key)
+
+    Returns an iterator pointing to the item with key \a key in the
+    map.
+
+    If the map contains no item with key \a key, the function
+    returns end().
+
+    \sa constFind(), value(), values(), lowerBound(), upperBound()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::find(const Key &key) const
+
+    \overload
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::constFind(const Key &key) const
+    \since 4.1
+
+    Returns an const iterator pointing to the item with key \a key in the
+    map.
+
+    If the map contains no item with key \a key, the function
+    returns constEnd().
+
+    \sa find()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::lowerBound(const Key &key)
+
+    Returns an iterator pointing to the first item with key \a key in
+    the map. If the map contains no item with key \a key, the
+    function returns an iterator to the nearest item with a greater
+    key.
+
+    \sa upperBound(), find()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::lowerBound(const Key &key) const
+
+    \overload
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::upperBound(const Key &key)
+
+    Returns an iterator pointing to the item that immediately follows
+    the last item with key \a key in the map. If the map contains no
+    item with key \a key, the function returns an iterator to the
+    nearest item with a greater key.
+
+    Example:
+    \snippet code/src_corelib_tools_qmap.cpp 17
+
+    \sa lowerBound(), find()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::upperBound(const Key &key) const
+
+    \overload
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::insert(const Key &key, const T &value)
+
+    Inserts a new item with the key \a key and a value of \a value.
+
+    If there is already an item with the key \a key, that item's value
+    is replaced with \a value.
+
+    \sa QMultiMap::insert()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::insert(const_iterator pos, const Key &key, const T &value)
+    \overload
+    \since 5.1
+    Inserts a new item with the key \a key and value \a value and with hint \a pos
+    suggesting where to do the insert.
+
+    If constBegin() is used as hint it indicates that the \a key is less than any key in the map
+    while constEnd() suggests that the \a key is (strictly) larger than any key in the map.
+    Otherwise the hint should meet the condition (\a pos - 1).key() < \a key <= pos.key().
+    If the hint \a pos is wrong it is ignored and a regular insert is done.
+
+    If there is already an item with the key \a key, that item's value
+    is replaced with \a value.
+
+    If the hint is correct and the map is unshared, the insert executes in amortized \l{constant time}.
+
+    When creating a map from sorted data inserting the largest key first with constBegin()
+    is faster than inserting in sorted order with constEnd(), since constEnd() - 1 (which is needed
+    to check if the hint is valid) needs \l{logarithmic time}.
+
+    \b {Note:} Be careful with the hint. Providing an iterator from an older shared instance might
+    crash but there is also a risk that it will silently corrupt both the map and the \a pos map.
+
+    \sa QMultiMap::insert()
+*/
+
+/*! \fn template <class Key, class T> void QMap<Key, T>::insert(const QMap<Key, T> &map)
+    \since 5.15
+
+    Inserts all the items in \a map into this map.
+
+    If a key is common to both maps, its value will be replaced with
+    the value stored in \a map.
+
+    \note If \a map contains multiple entries with the same key then the
+    final value of the key is undefined.
+
+    \sa QMultiMap::insert()
+*/
+
+/*! \typedef QMap::Iterator
+
+    Qt-style synonym for QMap<Key, T>::iterator.
+*/
+
+/*! \typedef QMap::ConstIterator
+
+    Qt-style synonym for QMap<Key, T>::const_iterator.
+*/
+
+/*! \typedef QMap::difference_type
+
+    Typedef for ptrdiff_t. Provided for STL compatibility.
+*/
+
+/*! \typedef QMap::key_type
+
+    Typedef for Key. Provided for STL compatibility.
+*/
+
+/*! \typedef QMap::mapped_type
+
+    Typedef for T. Provided for STL compatibility.
+*/
+
+/*! \typedef QMap::size_type
+
+    Typedef for int. Provided for STL compatibility.
+*/
+
+/*!
+    \fn template <class Key, class T> bool QMap<Key, T>::empty() const
+
+    This function is provided for STL compatibility. It is equivalent
+    to isEmpty(), returning true if the map is empty; otherwise
+    returning false.
+*/
+
+/*!
+  \fn template <class Key, class T> QPair<typename QMap<Key, T>::iterator, typename QMap<Key, T>::iterator> QMap<Key, T>::equal_range(const Key &key)
+
+  Returns a pair of iterators delimiting the range of values \c{[first, second)}, that
+  are stored under \a key.
+*/
+
+/*!
+    \fn template <class Key, class T> QPair<typename QMap<Key, T>::const_iterator, typename QMap<Key, T>::const_iterator> QMap<Key, T>::equal_range(const Key &key) const
+    \overload
+    \since 5.6
+*/
+
+
+/*! \class QMap::iterator
+    \inmodule QtCore
+    \brief The QMap::iterator class provides an STL-style non-const iterator for QMap.
+
+    QMap features both \l{STL-style iterators} and \l{Java-style
+    iterators}. The STL-style iterators are more low-level and more
+    cumbersome to use; on the other hand, they are slightly faster
+    and, for developers who already know STL, have the advantage of
+    familiarity.
+
+    QMap\<Key, T\>::iterator allows you to iterate over a QMap
+    and to modify the value (but not the key) stored under
+    a particular key. If you want to iterate over a const QMap, you
+    should use QMap::const_iterator. It is generally good practice to
+    use QMap::const_iterator on a non-const QMap as well, unless you
+    need to change the QMap through the iterator. Const iterators are
+    slightly faster, and can improve code readability.
+
+    The default QMap::iterator constructor creates an uninitialized
+    iterator. You must initialize it using a QMap function like
+    QMap::begin(), QMap::end(), or QMap::find() before you can
+    start iterating. Here's a typical loop that prints all the (key,
+    value) pairs stored in a map:
+
+    \snippet code/src_corelib_tools_qmap.cpp 18
+
+    Unlike QHash, which stores its items in an arbitrary order, QMap
+    stores its items ordered by key.
+
+    Let's see a few examples of things we can do with a
+    QMap::iterator that we cannot do with a QMap::const_iterator.
+    Here's an example that increments every value stored in the QMap
+    by 2:
+
+    \snippet code/src_corelib_tools_qmap.cpp 19
+
+    Here's an example that removes all the items whose key is a
+    string that starts with an underscore character:
+
+    \snippet code/src_corelib_tools_qmap.cpp 20
+
+    The call to QMap::erase() removes the item pointed to by the
+    iterator from the map, and returns an iterator to the next item.
+    Here's another way of removing an item while iterating:
+
+    \snippet code/src_corelib_tools_qmap.cpp 21
+
+    It might be tempting to write code like this:
+
+    \snippet code/src_corelib_tools_qmap.cpp 22
+
+    However, this will potentially crash in \c{++i}, because \c i is
+    a dangling iterator after the call to erase().
+
+    Multiple iterators can be used on the same map. If you add items
+    to the map, existing iterators will remain valid. If you remove
+    items from the map, iterators that point to the removed items
+    will become dangling iterators.
+
+    \warning Iterators on implicitly shared containers do not work
+    exactly like STL-iterators. You should avoid copying a container
+    while iterators are active on that container. For more information,
+    read \l{Implicit sharing iterator problem}.
+
+    \sa QMap::const_iterator, QMap::key_iterator, QMutableMapIterator
+*/
+
+/*! \typedef QMap::iterator::difference_type
+
+    \internal
+*/
+
+/*! \typedef QMap::iterator::iterator_category
+
+  A synonym for \e {std::bidirectional_iterator_tag} indicating
+  this iterator is a bidirectional iterator.
+*/
+
+/*! \typedef QMap::iterator::pointer
+
+    \internal
+*/
+
+/*! \typedef QMap::iterator::reference
+
+    \internal
+*/
+
+/*! \typedef QMap::iterator::value_type
+
+    \internal
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator::iterator()
+
+    Constructs an uninitialized iterator.
+
+    Functions like key(), value(), and operator++() must not be
+    called on an uninitialized iterator. Use operator=() to assign a
+    value to it before using it.
+
+    \sa QMap::begin(), QMap::end()
+*/
+
+/*! \fn template <class Key, class T> const Key &QMap<Key, T>::iterator::key() const
+
+    Returns the current item's key as a const reference.
+
+    There is no direct way of changing an item's key through an
+    iterator, although it can be done by calling QMap::erase()
+    followed by QMap::insert() or QMap::insertMulti().
+
+    \sa value()
+*/
+
+/*! \fn template <class Key, class T> T &QMap<Key, T>::iterator::value() const
+
+    Returns a modifiable reference to the current item's value.
+
+    You can change the value of an item by using value() on
+    the left side of an assignment, for example:
+
+    \snippet code/src_corelib_tools_qmap.cpp 23
+
+    \sa key(), operator*()
+*/
+
+/*! \fn template <class Key, class T> T &QMap<Key, T>::iterator::operator*() const
+
+    Returns a modifiable reference to the current item's value.
+
+    Same as value().
+
+    \sa key()
+*/
+
+/*! \fn template <class Key, class T> T *QMap<Key, T>::iterator::operator->() const
+
+    Returns a pointer to the current item's value.
+
+    \sa value()
+*/
+
+/*!
+    \fn template <class Key, class T> bool QMap<Key, T>::iterator::operator==(const iterator &other) const
+    \fn template <class Key, class T> bool QMap<Key, T>::iterator::operator==(const const_iterator &other) const
+
+    Returns \c true if \a other points to the same item as this
+    iterator; otherwise returns \c false.
+
+    \sa operator!=()
+*/
+
+/*!
+    \fn template <class Key, class T> bool QMap<Key, T>::iterator::operator!=(const iterator &other) const
+    \fn template <class Key, class T> bool QMap<Key, T>::iterator::operator!=(const const_iterator &other) const
+
+    Returns \c true if \a other points to a different item than this
+    iterator; otherwise returns \c false.
+
+    \sa operator==()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator &QMap<Key, T>::iterator::operator++()
+
+    The prefix ++ operator (\c{++i}) advances the iterator to the
+    next item in the map and returns an iterator to the new current
+    item.
+
+    Calling this function on QMap::end() leads to undefined results.
+
+    \sa operator--()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::iterator::operator++(int)
+
+    \overload
+
+    The postfix ++ operator (\c{i++}) advances the iterator to the
+    next item in the map and returns an iterator to the previously
+    current item.
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator &QMap<Key, T>::iterator::operator--()
+
+    The prefix -- operator (\c{--i}) makes the preceding item
+    current and returns an iterator pointing to the new current item.
+
+    Calling this function on QMap::begin() leads to undefined
+    results.
+
+    \sa operator++()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::iterator::operator--(int)
+
+    \overload
+
+    The postfix -- operator (\c{i--}) makes the preceding item
+    current and returns an iterator pointing to the previously
+    current item.
+*/
+
+/*! \class QMap::const_iterator
+    \inmodule QtCore
+    \brief The QMap::const_iterator class provides an STL-style const iterator for QMap.
+
+    QMap features both \l{STL-style iterators} and \l{Java-style
+    iterators}. The STL-style iterators are more low-level and more
+    cumbersome to use; on the other hand, they are slightly faster
+    and, for developers who already know STL, have the advantage of
+    familiarity.
+
+    QMap\<Key, T\>::const_iterator allows you to iterate over a QMap.
+    If you want to modify the QMap as you iterate
+    over it, you must use QMap::iterator instead. It is generally
+    good practice to use QMap::const_iterator on a non-const QMap as
+    well, unless you need to change the QMap through the iterator.
+    Const iterators are slightly faster, and can improve code
+    readability.
+
+    The default QMap::const_iterator constructor creates an
+    uninitialized iterator. You must initialize it using a QMap
+    function like QMap::constBegin(), QMap::constEnd(), or
+    QMap::find() before you can start iterating. Here's a typical
+    loop that prints all the (key, value) pairs stored in a map:
+
+    \snippet code/src_corelib_tools_qmap.cpp 24
+
+    Unlike QHash, which stores its items in an arbitrary order, QMap
+    stores its items ordered by key.
+
+    Multiple iterators can be used on the same map. If you add items
+    to the map, existing iterators will remain valid. If you remove
+    items from the map, iterators that point to the removed items
+    will become dangling iterators.
+
+    \warning Iterators on implicitly shared containers do not work
+    exactly like STL-iterators. You should avoid copying a container
+    while iterators are active on that container. For more information,
+    read \l{Implicit sharing iterator problem}.
+
+    \sa QMap::iterator, QMap::key_iterator, QMapIterator
+*/
+
+/*! \typedef QMap::const_iterator::difference_type
+
+    \internal
+*/
+
+/*! \typedef QMap::const_iterator::iterator_category
+
+  A synonym for \e {std::bidirectional_iterator_tag} indicating
+  this iterator is a bidirectional iterator.
+*/
+
+/*! \typedef QMap::const_iterator::pointer
+
+    \internal
+*/
+
+/*! \typedef QMap::const_iterator::reference
+
+    \internal
+*/
+
+/*! \typedef QMap::const_iterator::value_type
+
+    \internal
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator::const_iterator()
+
+    Constructs an uninitialized iterator.
+
+    Functions like key(), value(), and operator++() must not be
+    called on an uninitialized iterator. Use operator=() to assign a
+    value to it before using it.
+
+    \sa QMap::constBegin(), QMap::constEnd()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator::const_iterator(const iterator &other)
+
+    Constructs a copy of \a other.
+*/
+
+/*! \fn template <class Key, class T> const Key &QMap<Key, T>::const_iterator::key() const
+
+    Returns the current item's key.
+
+    \sa value()
+*/
+
+/*! \fn template <class Key, class T> const T &QMap<Key, T>::const_iterator::value() const
+
+    Returns the current item's value.
+
+    \sa key(), operator*()
+*/
+
+/*! \fn template <class Key, class T> const T &QMap<Key, T>::const_iterator::operator*() const
+
+    Returns the current item's value.
+
+    Same as value().
+
+    \sa key()
+*/
+
+/*! \fn template <class Key, class T> const T *QMap<Key, T>::const_iterator::operator->() const
+
+    Returns a pointer to the current item's value.
+
+    \sa value()
+*/
+
+/*! \fn template <class Key, class T> bool QMap<Key, T>::const_iterator::operator==(const const_iterator &other) const
+
+    Returns \c true if \a other points to the same item as this
+    iterator; otherwise returns \c false.
+
+    \sa operator!=()
+*/
+
+/*! \fn template <class Key, class T> bool QMap<Key, T>::const_iterator::operator!=(const const_iterator &other) const
+
+    Returns \c true if \a other points to a different item than this
+    iterator; otherwise returns \c false.
+
+    \sa operator==()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator &QMap<Key, T>::const_iterator::operator++()
+
+    The prefix ++ operator (\c{++i}) advances the iterator to the
+    next item in the map and returns an iterator to the new current
+    item.
+
+    Calling this function on QMap::end() leads to undefined results.
+
+    \sa operator--()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::const_iterator::operator++(int)
+
+    \overload
+
+    The postfix ++ operator (\c{i++}) advances the iterator to the
+    next item in the map and returns an iterator to the previously
+    current item.
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator &QMap<Key, T>::const_iterator::operator--()
+
+    The prefix -- operator (\c{--i}) makes the preceding item
+    current and returns an iterator pointing to the new current item.
+
+    Calling this function on QMap::begin() leads to undefined
+    results.
+
+    \sa operator++()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::const_iterator QMap<Key, T>::const_iterator::operator--(int)
+
+    \overload
+
+    The postfix -- operator (\c{i--}) makes the preceding item
+    current and returns an iterator pointing to the previously
+    current item.
+*/
+
+/*! \class QMap::key_iterator
+    \inmodule QtCore
+    \since 5.6
+    \brief The QMap::key_iterator class provides an STL-style const iterator for QMap keys.
+
+    QMap::key_iterator is essentially the same as QMap::const_iterator
+    with the difference that operator*() and operator->() return a key
+    instead of a value.
+
+    For most uses QMap::iterator and QMap::const_iterator should be used,
+    you can easily access the key by calling QMap::iterator::key():
+
+    \snippet code/src_corelib_tools_qmap.cpp keyiterator1
+
+    However, to have interoperability between QMap's keys and STL-style
+    algorithms we need an iterator that dereferences to a key instead
+    of a value. With QMap::key_iterator we can apply an algorithm to a
+    range of keys without having to call QMap::keys(), which is inefficient
+    as it costs one QMap iteration and memory allocation to create a temporary
+    QList.
+
+    \snippet code/src_corelib_tools_qmap.cpp keyiterator2
+
+    QMap::key_iterator is const, it's not possible to modify the key.
+
+    The default QMap::key_iterator constructor creates an uninitialized
+    iterator. You must initialize it using a QMap function like
+    QMap::keyBegin() or QMap::keyEnd().
+
+    \warning Iterators on implicitly shared containers do not work
+    exactly like STL-iterators. You should avoid copying a container
+    while iterators are active on that container. For more information,
+    read \l{Implicit sharing iterator problem}.
+
+    \sa QMap::const_iterator, QMap::iterator
+*/
+
+/*! \typedef QMap::key_iterator::difference_type
+    \internal
+*/
+
+/*! \typedef QMap::key_iterator::iterator_category
+    \internal
+*/
+
+/*! \typedef QMap::key_iterator::pointer
+    \internal
+*/
+
+/*! \typedef QMap::key_iterator::reference
+    \internal
+*/
+
+/*! \typedef QMap::key_iterator::value_type
+    \internal
+*/
+
+/*! \fn template <class Key, class T> const T &QMap<Key, T>::key_iterator::operator*() const
+
+    Returns the current item's key.
+*/
+
+/*! \fn template <class Key, class T> const T *QMap<Key, T>::key_iterator::operator->() const
+
+    Returns a pointer to the current item's key.
+*/
+
+/*! \fn template <class Key, class T> bool QMap<Key, T>::key_iterator::operator==(key_iterator other) const
+
+    Returns \c true if \a other points to the same item as this
+    iterator; otherwise returns \c false.
+
+    \sa operator!=()
+*/
+
+/*! \fn template <class Key, class T> bool QMap<Key, T>::key_iterator::operator!=(key_iterator other) const
+
+    Returns \c true if \a other points to a different item than this
+    iterator; otherwise returns \c false.
+
+    \sa operator==()
+*/
+
+/*!
+    \fn template <class Key, class T> QMap<Key, T>::key_iterator &QMap<Key, T>::key_iterator::operator++()
+
+    The prefix ++ operator (\c{++i}) advances the iterator to the
+    next item in the hash and returns an iterator to the new current
+    item.
+
+    Calling this function on QMap::keyEnd() leads to undefined results.
+
+    \sa operator--()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::key_iterator QMap<Key, T>::key_iterator::operator++(int)
+
+    \overload
+
+    The postfix ++ operator (\c{i++}) advances the iterator to the
+    next item in the hash and returns an iterator to the previous
+    item.
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::key_iterator &QMap<Key, T>::key_iterator::operator--()
+
+    The prefix -- operator (\c{--i}) makes the preceding item
+    current and returns an iterator pointing to the new current item.
+
+    Calling this function on QMap::keyBegin() leads to undefined
+    results.
+
+    \sa operator++()
+*/
+
+/*! \fn template <class Key, class T> QMap<Key, T>::key_iterator QMap<Key, T>::key_iterator::operator--(int)
+
+    \overload
+
+    The postfix -- operator (\c{i--}) makes the preceding item
+    current and returns an iterator pointing to the previous
+    item.
+*/
+
+/*! \fn template <class Key, class T> const_iterator QMap<Key, T>::key_iterator::base() const
+    Returns the underlying const_iterator this key_iterator is based on.
+*/
+
+/*! \typedef QMap::const_key_value_iterator
+    \inmodule QtCore
+    \since 5.10
+    \brief The QMap::const_key_value_iterator typedef provides an STL-style iterator for QMap.
+
+    QMap::const_key_value_iterator is essentially the same as QMap::const_iterator
+    with the difference that operator*() returns a key/value pair instead of a
+    value.
+
+    \sa QKeyValueIterator
+*/
+
+/*! \typedef QMap::key_value_iterator
+    \inmodule QtCore
+    \since 5.10
+    \brief The QMap::key_value_iterator typedef provides an STL-style iterator for QMap.
+
+    QMap::key_value_iterator is essentially the same as QMap::iterator
+    with the difference that operator*() returns a key/value pair instead of a
+    value.
+
+    \sa QKeyValueIterator
+*/
+
+/*! \fn template <class Key, class T> QDataStream &operator<<(QDataStream &out, const QMap<Key, T> &map)
+    \relates QMap
+
+    Writes the map \a map to stream \a out.
+
+    This function requires the key and value types to implement \c
+    operator<<().
+
+    \sa{Serializing Qt Data Types}{Format of the QDataStream operators}
+*/
+
+/*! \fn template <class Key, class T> QDataStream &operator>>(QDataStream &in, QMap<Key, T> &map)
+    \relates QMap
+
+    Reads a map from stream \a in into \a map.
+
+    This function requires the key and value types to implement \c
+    operator>>().
+
+    \sa{Serializing Qt Data Types}{Format of the QDataStream operators}
+*/