qmap.qdoc

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// 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.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
    \class QMap
    \inmodule QtCore
    \brief The QMap class is a template class that provides an associative array.
    \compares equality
 
    \ingroup tools
    \ingroup shared
 
    \reentrant
 
    QMap<Key, T> is one of Qt's generic \l{container classes}, where
    \a Key is the type used for lookup keys and \a T is the mapped value
    type. It stores (key, value) pairs and provides fast lookup by 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.
 
    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 only need to extract the values from a map (not the keys),
    you can also use range-based for:
 
    \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
    \memberswap{map}
*/
 
/*! \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> std::map<Key, T> QMap<Key, T>::toStdMap() &&
 
    \overload
    \since 6.0
 
    \note Calling this function will leave this QMap in the partially-formed state, in which
    the only valid operations are destruction or assignment of a new value.
*/
 
/*! \fn template <class Key, class T> bool QMap<Key, T>::operator==(const QMap<Key, T> &lhs, const QMap<Key, T> &rhs)
 
    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 QMap<Key, T>::operator!=(const QMap<Key, T> &lhs, const QMap<Key, T> &rhs)
 
    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> bool QMap<Key, T>::operator<(const QMap<Key, T> &lhs, const QMap<Key, T> &rhs)
    \since 6.12
 
    Returns \c true if \a lhs is
    \l {https://en.cppreference.com/w/cpp/algorithm/lexicographical_compare_three_way}
    {lexicographically less than} \a rhs; otherwise returns \c false.
 
//! [operator_uses_qt_lex_compare_three_way]
    This operator is available if both the key type \c Key and the mapped type
    \c T provide one of \c {operator<=>()} (in C++20 mode),
    \c {compareThreeWay()} helper method, or \c {operator<()}.
//! [operator_uses_qt_lex_compare_three_way]
*/
 
/*! \fn template <class Key, class T> bool QMap<Key, T>::operator>(const QMap<Key, T> &lhs, const QMap<Key, T> &rhs)
    \since 6.12
 
    Returns \c true if \a lhs is
    \l {https://en.cppreference.com/w/cpp/algorithm/lexicographical_compare_three_way}
    {lexicographically greater than} \a rhs; otherwise returns \c false.
 
    \include qmap.qdoc operator_uses_qt_lex_compare_three_way
*/
 
/*! \fn template <class Key, class T> bool QMap<Key, T>::operator<=(const QMap<Key, T> &lhs, const QMap<Key, T> &rhs)
    \since 6.12
 
    Returns \c true if \a lhs is
    \l {https://en.cppreference.com/w/cpp/algorithm/lexicographical_compare_three_way}
    {lexicographically less or equal than} \a rhs; otherwise returns \c false.
 
    \include qmap.qdoc operator_uses_qt_lex_compare_three_way
*/
 
/*! \fn template <class Key, class T> bool QMap<Key, T>::operator>=(const QMap<Key, T> &lhs, const QMap<Key, T> &rhs)
    \since 6.12
 
    Returns \c true if \a lhs is
    \l {https://en.cppreference.com/w/cpp/algorithm/lexicographical_compare_three_way}
    {lexicographically greater or equal than} \a rhs; otherwise returns \c false.
 
    \include qmap.qdoc operator_uses_qt_lex_compare_three_way
*/
 
/*! \fn template <class Key, class T> auto QMap<Key, T>::operator<=>(const QMap<Key, T> &lhs, const QMap<Key, T> &rhs)
    \since 6.12
 
    Compares the contents of \a lhs and \a rhs
    \l {https://en.cppreference.com/w/cpp/algorithm/lexicographical_compare_three_way}
    {lexicographically}. Returns the result of the strongest applicable category
    type.
 
//! [operator_in_cpp20_only]
    \note This operator is only available in C++20 mode when both the key type
    \c Key and the mapped type \c T meet the requirements of
    \c {std::three_way_comparable} concept or provide \c {operator<()}.
    In this case the \c{<}, \c{<=}, \c{>}, and \c{>=} operators are synthesized
    from \c {operator<=>()} and \c {operator==()}.
//! [operator_in_cpp20_only]
*/
 
/*! \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> template <typename Predicate> size_type QMap<Key, T>::removeIf(Predicate pred)
    \since 6.1
 
    Removes all elements for which the predicate \a pred returns true
    from the map.
 
    The function supports predicates which take either an argument of
    type \c{QMap<Key, T>::iterator}, or an argument of type
    \c{std::pair<const Key &, T &>}.
 
    Returns the number of elements removed, if any.
 
    \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 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.
 
    \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 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.
 
    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{constant 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{constant 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> auto QMap<Key, T>::asKeyValueRange() &
    \fn template <class Key, class T> auto QMap<Key, T>::asKeyValueRange() const &
    \fn template <class Key, class T> auto QMap<Key, T>::asKeyValueRange() &&
    \fn template <class Key, class T> auto QMap<Key, T>::asKeyValueRange() const &&
    \since 6.4
 
    Returns a range object that allows iteration over this map as
    key/value pairs. For instance, this range object can be used in a
    range-based for loop, in combination with a structured binding declaration:
 
    \snippet code/src_corelib_tools_qmap.cpp 28
 
    Note that both the key and the value obtained this way are
    references to the ones in the map. Specifically, mutating the value
    will modify the map itself.
 
    \sa QKeyValueIterator
*/
 
/*! \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.
 
    \note The iterator \a pos \e must be valid and dereferenceable.
 
    \sa remove()
*/
 
/*! \fn template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::erase(const_iterator first, const_iterator last)
    \since 6.0
 
    Removes the (key, value) pairs pointed to by the iterator range
    [\a first, \a last) from the map.
    Returns an iterator to the item in the map following the last removed element.
 
    \note The range \c {[first, last)} \e must be a valid range in \c {*this}.
 
    \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.
 
    Inserting a key/value pair with an existing key replaces the existing
    value.
 
    Returns an iterator pointing to the new/updated element.
*/
 
/*! \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.
 
    Returns an iterator pointing to the new/updated element.
*/
 
/*! \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.
*/
 
/*! \fn template <class Key, class T> void QMap<Key, T>::insert(QMap<Key, T> &&map)
    \since 5.15
 
    Moves all the items from \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.
 
    If \a map is shared, then the items will be copied instead.
*/
 
/*! \typedef QMap::Iterator
 
    Qt-style synonym for QMap::iterator.
*/
 
/*! \typedef QMap::ConstIterator
 
    Qt-style synonym for QMap::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> std::pair<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> std::pair<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<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.
 
    Here's an example that increments every value stored in the QMap
    by 2:
 
    \snippet code/src_corelib_tools_qmap.cpp 19
 
    To remove elements from a QMap you can use erase_if(QMap<Key, T> &map, Predicate pred):
 
    \snippet code/src_corelib_tools_qmap.cpp 21
 
    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, QMap::key_value_iterator
*/
 
/*! \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().
 
    \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 &lhs, const iterator &rhs)
    \fn template <class Key, class T> bool QMap<Key, T>::const_iterator::operator==(const const_iterator &lhs, const const_iterator &rhs)
 
    Returns \c true if \a lhs points to the same item as the \a rhs iterator;
    otherwise returns \c false.
 
    \sa operator!=()
*/
 
/*!
    \fn template <class Key, class T> bool QMap<Key, T>::iterator::operator!=(const iterator &lhs, const iterator &rhs)
    \fn template <class Key, class T> bool QMap<Key, T>::const_iterator::operator!=(const const_iterator &lhs, const const_iterator &rhs)
 
    Returns \c true if \a lhs points to a different item than the \a rhs iterator;
    otherwise returns \c false.
 
    \sa operator==()
*/
 
/*! \fn template <class Key, class T> QMap<Key, T>::iterator &QMap<Key, T>::iterator::operator++()
 
    The prefix \c{++} 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 \c{++} 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 \c{--} 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 \c{--} operator (\c{i--}) makes the preceding item
    current and returns an iterator pointing to the previously
    current item.
*/
 
/*! //! friends
    \fn [qmap-op-it-plus-step] template <class Key, class T> typename QMap<Key, T>::iterator QMap<Key, T>::iterator::operator+(QMap<Key, T>::iterator, difference_type n)
    \fn [qmap-op-step-plus-it] template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::iterator::operator+(difference_type n, QMap<Key, T>::iterator)
    \fn [qmap-op-it-minus-step] template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::iterator::operator-(QMap<Key, T>::iterator, difference_type n)
    \fn [qmap-op-step-minus-it] template <class Key, class T> QMap<Key, T>::iterator QMap<Key, T>::iterator::operator-(difference_type n, QMap<Key, T>::iterator)
 
    //! members
    \fn template <class Key, class T> typename QMap<Key, T>::iterator QMap<Key, T>::iterator::operator+=(QMap<Key, T>::iterator::difference_type n)
    \fn template <class Key, class T> typename QMap<Key, T>::iterator QMap<Key, T>::iterator::operator-=(QMap<Key, T>::iterator::difference_type n)
 
    \deprecated [6.2] Use \c{std::next}, \c{std::prev} or \c{std::advance} instead.
 
    Moves an iterator by \e{n} positions. These operations can be
    expensive for large values of \e{n}; QMap iterators are not
    random access.
*/
 
/*! \class QMap::const_iterator
    \inmodule QtCore
    \brief The QMap::const_iterator class provides an STL-style const iterator for QMap.
 
    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::cbegin(), QMap::cend(), or
    QMap::constFind() 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
 
    Here's an example that removes all the items whose value is greater than 10:
 
    \snippet code/src_corelib_tools_qmap.cpp 20
 
    And here the same behavior with erase_if()
 
    \snippet code/src_corelib_tools_qmap.cpp 21
 
    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, QMap::const_key_value_iterator
*/
 
/*! \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> QMap<Key, T>::const_iterator &QMap<Key, T>::const_iterator::operator++()
 
    The prefix \c{++} 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 \c{++} 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 \c{--} 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 \c{--} operator (\c{i--}) makes the preceding item
    current and returns an iterator pointing to the previously
    current item.
*/
 
/*! //! friends
    \fn [qmap-op-it-plus-step-const] template <class Key, class T> QMap<Key, T>::const_iterator::operator+(QMap<Key, T>::const_iterator, difference_type n)
    \fn [qmap-op-step-plus-it-const] template <class Key, class T> QMap<Key, T>::operator+(difference_type n, QMap<Key, T>::const_iterator)
    \fn [qmap-op-it-minus-step-const] template <class Key, class T> QMap<Key, T>::operator-(QMap<Key, T>::const_iterator, difference_type n)
    \fn [qmap-op-step-minus-it-const] template <class Key, class T> QMap<Key, T>::operator-(difference_type n, QMap<Key, T>::const_iterator)
 
    //! members
    \fn template <class Key, class T> typename QMap<Key, T>::const_iterator QMap<Key, T>::const_iterator::operator+=(QMap<Key, T>::const_iterator::difference_type n)
    \fn template <class Key, class T> typename QMap<Key, T>::const_iterator QMap<Key, T>::const_iterator::operator-=(QMap<Key, T>::const_iterator::difference_type n)
 
    \deprecated [6.2] Use \c{std::next}, \c{std::prev} or \c{std::advance} instead.
 
    Moves an iterator by \e{n} positions. These operations can be
    expensive for large values of \e{n}. QMap iterators are not
    random access.
*/
 
/*! \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 \c{++} 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 \c{++} 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 \c{--} 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 \c{--} 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}
*/
 
/*! \fn template <typename Key, typename T, typename Predicate> qsizetype erase_if(QMap<Key, T> &map, Predicate pred)
    \relates QMap
    \since 6.1
 
    Removes all elements for which the predicate \a pred returns true
    from the map \a map.
 
    The function supports predicates which take either an argument of
    type \c{QMap<Key, T>::iterator}, or an argument of type
    \c{std::pair<const Key &, T &>}.
 
    Returns the number of elements removed, if any.
*/
 
/*!
    \fn template <class Key, class T> size_t QMap<Key, T>::qHash(const QMap &key, size_t seed) noexcept
    \since 6.8
    \qhashTS{QMap}{Key}{T}
*/