QVector: add {const_,}reverse_iterator, {c,}r{begin,end}()

[ChangeLog][QtCore][QVector] Added rbegin(), crbegin(), rend(), crend(),
and reverse_iterator and const_reverse_iterator typedefs.

Task-number: QTBUG-25919
Change-Id: I8dea52a08e7b1a4442e034c22b83be4d25dc2303
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qvector.cpp

@@ -871,6 +871,52 @@
     \sa constBegin(), end()
 */
 
+/*! \fn QVector::reverse_iterator QVector::rbegin()
+    \since 5.6
+
+    Returns a \l{STL-style iterators}{STL-style} reverse iterator pointing to the first
+    item in the vector, in reverse order.
+
+    \sa begin(), crbegin(), rend()
+*/
+
+/*! \fn QVector::const_reverse_iterator QVector::rbegin() const
+    \since 5.6
+    \overload
+*/
+
+/*! \fn QVector::const_reverse_iterator QVector::crbegin() const
+    \since 5.6
+
+    Returns a const \l{STL-style iterators}{STL-style} reverse iterator pointing to the first
+    item in the vector, in reverse order.
+
+    \sa begin(), rbegin(), rend()
+*/
+
+/*! \fn QVector::reverse_iterator QVector::rend()
+    \since 5.6
+
+    Returns a \l{STL-style iterators}{STL-style} reverse iterator pointing to one past
+    the last item in the vector, in reverse order.
+
+    \sa end(), crend(), rbegin()
+*/
+
+/*! \fn QVector::const_reverse_iterator QVector::rend() const
+    \since 5.6
+    \overload
+*/
+
+/*! \fn QVector::const_reverse_iterator QVector::crend() const
+    \since 5.6
+
+    Returns a const \l{STL-style iterators}{STL-style} reverse iterator pointing to one
+    past the last item in the vector, in reverse order.
+
+    \sa end(), rend(), rbegin()
+*/
+
 /*! \fn QVector::iterator QVector::erase(iterator pos)
 
     Removes the item pointed to by the iterator \a pos from the
@@ -1061,6 +1107,38 @@
     \sa QVector::constBegin(), QVector::constEnd(), QVector::iterator, QVectorIterator
 */
 
+/*! \typedef QVector::reverse_iterator
+    \since 5.6
+
+    The QVector::reverse_iterator typedef provides an STL-style non-const
+    reverse iterator for QVector.
+
+    It is simply a typedef for \c{std::reverse_iterator<T*>}.
+
+    \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 QVector::rbegin(), QVector::rend(), QVector::const_reverse_iterator, QVector::iterator
+*/
+
+/*! \typedef QVector::const_reverse_iterator
+    \since 5.6
+
+    The QVector::const_reverse_iterator typedef provides an STL-style const
+    reverse iterator for QVector.
+
+    It is simply a typedef for \c{std::reverse_iterator<const T*>}.
+
+    \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 QVector::rbegin(), QVector::rend(), QVector::reverse_iterator, QVector::const_iterator
+*/
+
 /*! \typedef QVector::Iterator
 
     Qt-style synonym for QVector::iterator.

src/corelib/tools/qvector.h

@@ -175,6 +175,8 @@ public:
     // STL-style
     typedef typename Data::iterator iterator;
     typedef typename Data::const_iterator const_iterator;
+    typedef std::reverse_iterator<iterator> reverse_iterator;
+    typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 #if !defined(QT_STRICT_ITERATORS) || defined(Q_QDOC)
     inline iterator begin() { detach(); return d->begin(); }
     inline const_iterator begin() const { return d->constBegin(); }
@@ -194,6 +196,12 @@ public:
     inline const_iterator cend(const_iterator = const_iterator()) const { return d->constEnd(); }
     inline const_iterator constEnd(const_iterator = const_iterator()) const { return d->constEnd(); }
 #endif
+    reverse_iterator rbegin() { return reverse_iterator(end()); }
+    reverse_iterator rend() { return reverse_iterator(begin()); }
+    const_reverse_iterator rbegin() const { return const_reverse_iterator(end()); }
+    const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }
+    const_reverse_iterator crbegin() const { return const_reverse_iterator(end()); }
+    const_reverse_iterator crend() const { return const_reverse_iterator(begin()); }
     iterator insert(iterator before, int n, const T &x);
     inline iterator insert(iterator before, const T &x) { return insert(before, 1, x); }
     iterator erase(iterator begin, iterator end);

tests/auto/corelib/tools/qvector/tst_qvector.cpp

@@ -248,6 +248,7 @@ private slots:
     void resizeComplex_data() const;
     void resizeComplex() const;
     void resizeCtorAndDtor() const;
+    void reverseIterators() const;
     void sizeInt() const;
     void sizeMovable() const;
     void sizeCustom() const;
@@ -1914,6 +1915,21 @@ void tst_QVector::resizeCtorAndDtor() const
     QCOMPARE(Custom::counter.loadAcquire(), items);
 }
 
+void tst_QVector::reverseIterators() const
+{
+    QVector<int> v;
+    v << 1 << 2 << 3 << 4;
+    QVector<int> vr = v;
+    std::reverse(vr.begin(), vr.end());
+    const QVector<int> &cvr = vr;
+    QVERIFY(std::equal(v.begin(), v.end(), vr.rbegin()));
+    QVERIFY(std::equal(v.begin(), v.end(), vr.crbegin()));
+    QVERIFY(std::equal(v.begin(), v.end(), cvr.rbegin()));
+    QVERIFY(std::equal(vr.rbegin(), vr.rend(), v.begin()));
+    QVERIFY(std::equal(vr.crbegin(), vr.crend(), v.begin()));
+    QVERIFY(std::equal(cvr.rbegin(), cvr.rend(), v.begin()));
+}
+
 template<typename T>
 void tst_QVector::size() const
 {