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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
    \class QSet
    \inmodule QtCore
    \brief The QSet class is a template class that provides a hash-table-based set.
 
    \ingroup tools
    \ingroup shared
    \reentrant
 
 
    QSet<T> is one of Qt's generic \l{container classes}. It stores
    values in an unspecified order and provides very fast lookup of
    the values. Internally, QSet<T> is implemented as a QHash.
 
    Here's an example QSet with QString values:
 
    \snippet code/doc_src_qset.cpp 0
 
    To insert a value into the set, use insert():
 
    \snippet code/doc_src_qset.cpp 1
 
    Another way to insert items into the set is to use \l operator<<():
 
    \snippet code/doc_src_qset.cpp 2
 
    To test whether an item belongs to the set or not, use contains():
 
    \snippet code/doc_src_qset.cpp 3
 
    If you want to navigate through all the values stored in a QSet,
    you can use an iterator. QSet supports both \l{Java-style
    iterators} (QSetIterator and QMutableSetIterator) and \l{STL-style
    iterators} (QSet::iterator and QSet::const_iterator). Here's how
    to iterate over a QSet<QWidget *> using a Java-style iterator:
 
    \snippet code/doc_src_qset.cpp 4
 
    Here's the same code, but using an STL-style iterator:
 
    \snippet code/doc_src_qset.cpp 5
 
    QSet is unordered, so an iterator's sequence cannot be assumed to
    be predictable. If ordering by key is required, use a QMap.
 
    To navigate through a QSet, you can also use range-based for:
 
    \snippet code/doc_src_qset.cpp 6
 
    Items can be removed from the set using remove(). There is also a
    clear() function that removes all items.
 
    QSet's value data type must be an \l{assignable data type}. You
    cannot, for example, store a QWidget as a value; instead, store a
    QWidget *. In addition, the type must provide \c operator==(), and
    there must also be a global qHash() function that returns a hash
    value for an argument of the key's type. See the QHash
    documentation for a list of types supported by qHash().
 
    Internally, QSet uses a hash table to perform lookups. The hash
    table automatically grows and shrinks to provide fast lookups
    without wasting memory. You can still control the size of the hash
    table by calling reserve(), if you already know approximately how
    many elements the QSet will contain, but this isn't necessary to
    obtain good performance. You can also call capacity() to retrieve
    the hash table's size.
 
    \sa QSetIterator, QMutableSetIterator, QHash, QMap
*/
 
/*!
    \fn template <class T> QSet<T>::QSet()
 
    Constructs an empty set.
 
    \sa clear()
*/
 
/*! \fn template <class T> QSet<T>::QSet(std::initializer_list<T> list)
    \since 5.1
 
    Constructs a set with a copy of each of the elements in the
    initializer list \a list.
*/
 
/*! \fn template <class T> template<typename InputIterator> QSet<T>::QSet(InputIterator first, InputIterator last)
    \since 5.14
 
    Constructs a set with the contents in the iterator range [\a first, \a last).
 
    The value type of \c InputIterator must be convertible to \c T.
 
    \note If the range [\a first, \a last) contains duplicate elements,
    the first one is retained.
*/
 
/*!
    \fn template <class T> void QSet<T>::swap(QSet<T> &other)
 
    Swaps set \a other with this set. This operation is very fast and
    never fails.
*/
 
/*!
    \fn template <class T> bool QSet<T>::operator==(const QSet<T> &other) const
 
    Returns \c true if the \a other set is equal to this set; otherwise
    returns \c false.
 
    Two sets are considered equal if they contain the same elements.
 
    This function requires the value type to implement \c operator==().
 
    \sa operator!=()
*/
 
/*!
    \fn template <class T> bool QSet<T>::operator!=(const QSet<T> &other) const
 
    Returns \c true if the \a other set is not equal to this set; otherwise
    returns \c false.
 
    Two sets are considered equal if they contain the same elements.
 
    This function requires the value type to implement \c operator==().
 
    \sa operator==()
*/
 
/*!
    \fn template <class T> int QSet<T>::size() const
 
    Returns the number of items in the set.
 
    \sa isEmpty(), count()
*/
 
/*!
    \fn template <class T> bool QSet<T>::isEmpty() const
 
    Returns \c true if the set contains no elements; otherwise returns
    false.
 
    \sa size()
*/
 
/*!
    \fn template <class T> int QSet<T>::capacity() const
 
    Returns the number of buckets in the set's internal hash
    table.
 
    The sole purpose of this function is to provide a means of fine
    tuning QSet's memory usage. In general, you will rarely ever need
    to call this function. If you want to know how many items are in
    the set, call size().
 
    \sa reserve(), squeeze()
*/
 
/*! \fn template <class T> void QSet<T>::reserve(qsizetype size)
 
    Ensures that the set's internal hash table consists of at
    least \a size buckets.
 
    This function is useful for code that needs to build a huge set
    and wants to avoid repeated reallocation. For example:
 
    \snippet code/doc_src_qset.cpp 7
 
    Ideally, \a size should be slightly more than the maximum number
    of elements expected in the set. \a size doesn't have to be prime,
    because QSet will use a prime number internally anyway. If \a size
    is an underestimate, the worst that will happen is that the QSet
    will be a bit slower.
 
    In general, you will rarely ever need to call this function.
    QSet's internal hash table automatically shrinks or grows to
    provide good performance without wasting too much memory.
 
    \sa squeeze(), capacity()
*/
 
/*!
    \fn template <class T> void QSet<T>::squeeze()
 
    Reduces the size of the set's internal hash table to save
    memory.
 
    The sole purpose of this function is to provide a means of fine
    tuning QSet's memory usage. In general, you will rarely ever
    need to call this function.
 
    \sa reserve(), capacity()
*/
 
/*!
    \fn template <class T> void QSet<T>::detach()
 
    \internal
 
    Detaches this set from any other sets with which it may share
    data.
 
    \sa isDetached()
*/
 
/*! \fn template <class T> bool QSet<T>::isDetached() const
 
    \internal
 
    Returns \c true if the set's internal data isn't shared with any
    other set object; otherwise returns \c false.
 
    \sa detach()
*/
 
/*!
    \fn template <class T> void QSet<T>::setSharable(bool sharable)
    \internal
*/
 
/*!
    \fn template <class T> void QSet<T>::clear()
 
    Removes all elements from the set.
 
    \sa remove()
*/
 
/*!
    \fn template <class T> bool QSet<T>::remove(const T &value)
 
    Removes any occurrence of item \a value from the set. Returns
    true if an item was actually removed; otherwise returns \c false.
 
    \sa contains(), insert()
*/
 
/*!
    \fn template <class T> QSet<T>::iterator QSet<T>::erase(const_iterator pos)
    \since 5.7
 
    Removes the item at the iterator position \a pos from the set, and
    returns an iterator positioned at the next item in the set.
 
    Unlike remove(), this function never causes QSet to rehash its
    internal data structure. This means that it can safely be called
    while iterating, and won't affect the order of items in the set.
 
    \note The iterator \a pos \e must be valid and dereferenceable. Calling this
    method on any other iterator, including its own \l end(), results in
    undefined behavior. In particular, even the \l begin() iterator of an empty
    set cannot be dereferenced.
 
    \sa remove(), find()
*/
 
/*! \fn template <class T> QSet<T>::const_iterator QSet<T>::find(const T &value) const
    \since 4.2
 
    Returns a const iterator positioned at the item \a value in the
    set. If the set contains no item \a value, the function returns
    constEnd().
 
    \sa constFind(), contains()
*/
 
/*! \fn template <class T> QSet<T>::iterator QSet<T>::find(const T &value)
    \since 4.2
    \overload
 
    Returns a non-const iterator positioned at the item \a value in
    the set. If the set contains no item \a value, the function
    returns end().
*/
 
/*! \fn template <class T> QSet<T>::const_iterator QSet<T>::constFind(const T &value) const
    \since 4.2
 
    Returns a const iterator positioned at the item \a value in the
    set. If the set contains no item \a value, the function returns
    constEnd().
 
    \sa find(), contains()
*/
 
/*!
    \fn template <class T> bool QSet<T>::contains(const T &value) const
 
    Returns \c true if the set contains item \a value; otherwise returns
    false.
 
    \sa insert(), remove(), find()
*/
 
/*!
    \fn template <class T> bool QSet<T>::contains(const QSet<T> &other) const
    \since 4.6
 
    Returns \c true if the set contains all items from the \a other set;
    otherwise returns \c false.
 
    \sa insert(), remove(), find()
*/
 
/*! \fn template <class T> QSet<T>::const_iterator QSet<T>::begin() const
 
    Returns a const \l{STL-style iterators}{STL-style iterator} positioned at the first
    item in the set.
 
    \sa constBegin(), end()
*/
 
/*! \fn template <class T> QSet<T>::iterator QSet<T>::begin()
    \since 4.2
    \overload
 
    Returns a non-const \l{STL-style iterators}{STL-style iterator} positioned at the first
    item in the set.
*/
 
/*! \fn template <class T> QSet<T>::const_iterator QSet<T>::cbegin() const
    \since 5.0
 
    Returns a const \l{STL-style iterators}{STL-style iterator} positioned at the first
    item in the set.
 
    \sa begin(), cend()
*/
 
/*! \fn template <class T> QSet<T>::const_iterator QSet<T>::constBegin() const
 
    Returns a const \l{STL-style iterators}{STL-style iterator} positioned at the first
    item in the set.
 
    \sa begin(), constEnd()
*/
 
/*! \fn template <class T> QSet<T>::const_iterator QSet<T>::end() const
 
    Returns a const \l{STL-style iterators}{STL-style iterator} positioned at the imaginary
    item after the last item in the set.
 
    \sa constEnd(), begin()
*/
 
/*! \fn template <class T> QSet<T>::iterator QSet<T>::end()
    \since 4.2
    \overload
 
    Returns a non-const \l{STL-style iterators}{STL-style iterator} pointing to the
    imaginary item after the last item in the set.
*/
 
/*! \fn template <class T> QSet<T>::const_iterator QSet<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 set.
 
    \sa cbegin(), end()
*/
 
/*! \fn template <class T> QSet<T>::const_iterator QSet<T>::constEnd() const
 
    Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary
    item after the last item in the set.
 
    \sa constBegin(), end()
*/
 
/*!
    \typedef QSet::Iterator
    \since 4.2
 
    Qt-style synonym for QSet::iterator.
*/
 
/*!
    \typedef QSet::ConstIterator
 
    Qt-style synonym for QSet::const_iterator.
*/
 
/*!
    \typedef QSet::const_pointer
 
    Typedef for const T *. Provided for STL compatibility.
*/
 
/*!
    \typedef QSet::const_reference
 
    Typedef for const T &. Provided for STL compatibility.
*/
 
/*!
    \typedef QSet::difference_type
 
    Typedef for const ptrdiff_t. Provided for STL compatibility.
*/
 
/*!
    \typedef QSet::key_type
 
    Typedef for T. Provided for STL compatibility.
*/
 
/*!
    \typedef QSet::pointer
 
    Typedef for T *. Provided for STL compatibility.
*/
 
/*!
    \typedef QSet::reference
 
    Typedef for T &. Provided for STL compatibility.
*/
 
/*!
    \typedef QSet::size_type
 
    Typedef for int. Provided for STL compatibility.
*/
 
/*!
    \typedef QSet::value_type
 
    Typedef for T. Provided for STL compatibility.
*/
 
/*!
    \fn template <class T> QSet<T>::iterator QSet<T>::insert(const T &value)
 
    Inserts item \a value into the set, if \a value isn't already
    in the set, and returns an iterator pointing at the inserted
    item.
 
    \sa operator<<(), remove(), contains()
*/
 
/*!
    \fn template <class T> QSet<T> &QSet<T>::unite(const QSet<T> &other)
 
    Each item in the \a other set that isn't already in this set is
    inserted into this set. A reference to this set is returned.
 
    \sa operator|=(), intersect(), subtract()
*/
 
/*!
    \fn template <class T> QSet<T> &QSet<T>::intersect(const QSet<T> &other)
 
    Removes all items from this set that are not contained in the
    \a other set. A reference to this set is returned.
 
    \sa intersects(), operator&=(), unite(), subtract()
*/
 
/*!
    \fn template <class T> bool QSet<T>::intersects(const QSet<T> &other) const
    \since 5.6
 
    Returns \c true if this set has at least one item in common with
    \a other.
 
    \sa contains(), intersect()
*/
 
/*!
    \fn template <class T> QSet<T> &QSet<T>::subtract(const QSet<T> &other)
 
    Removes all items from  this set that are contained in the
    \a other set. Returns a reference to this set.
 
    \sa operator-=(), unite(), intersect()
*/
 
/*!
    \fn template <class T> bool QSet<T>::empty() const
 
    Returns \c true if the set is empty. This function is provided
    for STL compatibility. It is equivalent to isEmpty().
*/
 
/*!
    \fn template <class T> QSet<T>::iterator QSet<T>::insert(const_iterator it, const T &value)
    \overload
    \since 6.1
 
    Inserts item \a value into the set, if \a value isn't already
    in the set, and returns an iterator pointing at the inserted
    item.
 
    The iterator \a it is ignored.
 
    This function is provided for compatibility with the STL.
 
    \sa operator<<(), remove(), contains()
*/
 
/*!
    \fn template <class T> bool QSet<T>::count() const
 
    Same as size().
*/
 
/*!
    \fn template <class T> QSet<T> &QSet<T>::operator<<(const T &value)
    \fn template <class T> QSet<T> &QSet<T>::operator+=(const T &value)
    \fn template <class T> QSet<T> &QSet<T>::operator|=(const T &value)
 
    Inserts a new item \a value and returns a reference to the set.
    If \a value already exists in the set, the set is left unchanged.
 
    \sa insert()
*/
 
/*!
    \fn template <class T> QSet<T> &QSet<T>::operator-=(const T &value)
 
    Removes the occurrence of item \a value from the set, if
    it is found, and returns a reference to the set. If the
    \a value is not contained the set, nothing is removed.
 
    \sa remove()
*/
 
/*!
    \fn template <class T> QSet<T> &QSet<T>::operator|=(const QSet<T> &other)
    \fn template <class T> QSet<T> &QSet<T>::operator+=(const QSet<T> &other)
 
    Same as \l {unite()} {unite(\a other)}.
 
    \sa operator|(), operator&=(), operator-=()
*/
 
/*!
    \fn template <class T> QSet<T> &QSet<T>::operator&=(const QSet<T> &other)
 
    Same as \l {intersect()} {intersect(\a other)}.
 
    \sa operator&(), operator|=(), operator-=()
*/
 
/*!
    \fn template <class T> QSet<T> &QSet<T>::operator&=(const T &value)
 
    \overload
 
    Same as \l {intersect()} {intersect(\e{other})}, if we consider \e other to be a set
    that contains the singleton \a value.
*/
 
 
/*!
    \fn template <class T> QSet<T> &QSet<T>::operator-=(const QSet<T> &other)
 
    Same as \l {subtract()} {subtract(\a{other})}.
 
    \sa operator-(), operator|=(), operator&=()
*/
 
/*!
    \fn template <class T> QSet<T> QSet<T>::operator|(const QSet<T> &other) const
    \fn template <class T> QSet<T> QSet<T>::operator+(const QSet<T> &other) const
 
    Returns a new QSet that is the union of this set and the
    \a other set.
 
    \sa unite(), operator|=(), operator&(), operator-()
*/
 
/*!
    \fn template <class T> QSet<T> QSet<T>::operator&(const QSet<T> &other) const
 
    Returns a new QSet that is the intersection of this set and the
    \a other set.
 
    \sa intersect(), operator&=(), operator|(), operator-()
*/
 
/*!
    \fn template <class T> QSet<T> QSet<T>::operator-(const QSet<T> &other) const
 
    Returns a new QSet that is the set difference of this set and
    the \a other set, i.e., this set - \a other set.
 
    \sa subtract(), operator-=(), operator|(), operator&()
*/
 
/*!
    \class QSet::iterator
    \inmodule QtCore
    \since 4.2
    \brief The QSet::iterator class provides an STL-style non-const iterator for QSet.
 
    QSet 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.
 
    QSet<T>::iterator allows you to iterate over a QSet and to remove
    items (using QSet::erase()) while you iterate. (QSet doesn't let
    you \e modify a value through an iterator, because that
    would potentially require moving the value in the internal hash
    table used by QSet.) If you want to iterate over a const QSet,
    you should use QSet::const_iterator. It is generally good
    practice to use QSet::const_iterator on a non-const QSet as well,
    unless you need to change the QSet through the iterator. Const
    iterators are slightly faster, and can improve code readability.
 
    The default QSet::iterator constructor creates an uninitialized
    iterator. You must initialize it using a function like
    QSet::begin(), QSet::end(), or QSet::insert() before you can
    start iterating. Here's a typical loop that prints all the items
    stored in a set:
 
    \snippet code/doc_src_qset.cpp 8
 
    Here's a loop that removes certain items (all those that start
    with 'J') from a set while iterating:
 
    \snippet code/doc_src_qset.cpp 9
 
    STL-style iterators can be used as arguments to \l{generic
    algorithms}. For example, here's how to find an item in the set
    using the qFind() algorithm:
 
    \snippet code/doc_src_qset.cpp 10
 
    Multiple iterators can be used on the same set.
 
    \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 QSet::const_iterator, QMutableSetIterator
*/
 
/*!
    \class QSet::const_iterator
    \inmodule QtCore
    \brief The QSet::const_iterator class provides an STL-style const iterator for QSet.
    \since 4.2
 
    QSet 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.
 
    QSet<Key, T>::const_iterator allows you to iterate over a QSet.
    If you want to modify the QSet as you iterate over it, you must
    use QSet::iterator instead. It is generally good practice to use
    QSet::const_iterator on a non-const QSet as well, unless you need
    to change the QSet through the iterator. Const iterators are
    slightly faster, and can improve code readability.
 
    The default QSet::const_iterator constructor creates an
    uninitialized iterator. You must initialize it using a function
    like QSet::begin(), QSet::end(), or QSet::insert() before you can
    start iterating. Here's a typical loop that prints all the items
    stored in a set:
 
    \snippet code/doc_src_qset.cpp 11
 
    STL-style iterators can be used as arguments to \l{generic
    algorithms}. For example, here's how to find an item in the set
    using the qFind() algorithm:
 
    \snippet code/doc_src_qset.cpp 12
 
    \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 QSet::iterator, QSetIterator
*/
 
/*!
    \fn template <class T> QSet<T>::iterator::iterator()
    \fn template <class T> QSet<T>::const_iterator::const_iterator()
 
    Constructs an uninitialized iterator.
 
    Functions like operator*() and operator++() should not be called
    on an uninitialized iterator. Use operator=() to assign a value
    to it before using it.
 
    \sa QSet::begin(), QSet::end()
*/
 
/*!
    \fn template <class T> QSet<T>::iterator::iterator(typename Hash::iterator i)
    \fn template <class T> QSet<T>::const_iterator::const_iterator(typename Hash::const_iterator i)
 
    \internal
*/
 
/*!
  \typedef QSet::iterator::iterator_category
  \typedef QSet::const_iterator::iterator_category
 
  Synonyms for \e {std::bidirectional_iterator_tag} indicating
  these iterators are bidirectional iterators.
 */
 
/*!
    \typedef QSet::iterator::difference_type
    \typedef QSet::const_iterator::difference_type
 
    \internal
*/
 
/*!
    \typedef QSet::iterator::value_type
    \typedef QSet::const_iterator::value_type
 
    \internal
*/
 
/*!
    \typedef QSet::iterator::pointer
    \typedef QSet::const_iterator::pointer
 
    \internal
*/
 
/*!
    \typedef QSet::iterator::reference
    \typedef QSet::const_iterator::reference
 
    \internal
*/
 
/*!
    \fn template <class T> QSet<T>::iterator::iterator(const iterator &other)
    \fn template <class T> QSet<T>::const_iterator::const_iterator(const const_iterator &other)
 
    Constructs a copy of \a other.
*/
 
/*!
    \fn template <class T> QSet<T>::const_iterator::const_iterator(const iterator &other)
    \since 4.2
    \overload
 
    Constructs a copy of \a other.
*/
 
/*!
    \fn template <class T> QSet<T>::iterator &QSet<T>::iterator::operator=(const iterator &other)
    \fn template <class T> QSet<T>::const_iterator &QSet<T>::const_iterator::operator=(const const_iterator &other)
 
    Assigns \a other to this iterator.
*/
 
/*!
    \fn template <class T> const T &QSet<T>::iterator::operator*() const
    \fn template <class T> const T &QSet<T>::const_iterator::operator*() const
 
    Returns a reference to the current item.
 
    \sa operator->()
*/
 
/*!
    \fn template <class T> const T *QSet<T>::iterator::operator->() const
    \fn template <class T> const T *QSet<T>::const_iterator::operator->() const
 
    Returns a pointer to the current item.
 
    \sa operator*()
*/
 
/*!
    \fn template <class T> bool QSet<T>::iterator::operator==(const iterator &other) const
    \fn template <class T> bool QSet<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 T> bool QSet<T>::iterator::operator==(const const_iterator &other) const
    \fn template <class T> bool QSet<T>::iterator::operator!=(const const_iterator &other) const
 
    \overload
*/
 
/*!
    \fn template <class T> bool QSet<T>::iterator::operator!=(const iterator &other) const
    \fn template <class T> bool QSet<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 T> QSet<T>::iterator &QSet<T>::iterator::operator++()
    \fn template <class T> QSet<T>::const_iterator &QSet<T>::const_iterator::operator++()
 
    The prefix ++ operator (\c{++it}) advances the iterator to the
    next item in the set and returns an iterator to the new current
    item.
 
    Calling this function on QSet<T>::constEnd() leads to
    undefined results.
*/
 
/*!
    \fn template <class T> QSet<T>::iterator QSet<T>::iterator::operator++(int)
    \fn template <class T> QSet<T>::const_iterator QSet<T>::const_iterator::operator++(int)
 
    \overload
 
    The postfix ++ operator (\c{it++}) advances the iterator to the
    next item in the set and returns an iterator to the previously
    current item.
*/
 
/*! \fn template <class T> QList<T> QSet<T>::values() const
 
    Returns a new QList containing the elements in the set. The
    order of the elements in the QList is undefined.
 
    \include containers-range-constructor.qdocinc
 
    This function creates a new list, in \l {linear time}. The time and memory
    use that entails can be avoided by iterating from \l constBegin() to
    \l constEnd().
*/
 
 
/*!
    \fn template <class T> QDataStream &operator<<(QDataStream &out, const QSet<T> &set)
    \relates QSet
 
    Writes the \a set to stream \a out.
 
    This function requires the value type to implement \c operator<<().
 
    \sa{Serializing Qt Data Types}{Format of the QDataStream operators}
*/
 
/*!
    \fn template <class T> QDataStream &operator>>(QDataStream &in, QSet<T> &set)
    \relates QSet
 
    Reads a set from stream \a in into \a set.
 
    This function requires the value type to implement \c operator>>().
 
    \sa{Serializing Qt Data Types}{Format of the QDataStream operators}
*/
 
/*!
    \fn template <class T> size_t qHash(const QSet<T> &key, size_t seed = 0)
    \relates QHash
    \since 5.5
 
    Returns the hash value for the \a key, using \a seed to seed the calculation.
 
    The hash value is independent of the order of elements in \a key, that is, sets
    that contain the same elements hash to the same value.
*/
 
/*! \fn template <class T, class Predicate> qsizetype erase_if(QSet<T> &set, Predicate pred)
    \relates QSet
    \since 6.1
 
    Removes all elements for which the predicate \a pred returns true
    from the set \a set. Returns the number of elements removed, if
    any.
*/