QList: add relational operators <,<=,>,>=

std::vector has them, too.

[ChangeLog][QtCore][QList] Added relational operators <, <=, >, >= if the element
type supports operator<.

Change-Id: Id2bd905e92c0365ad9f439d49908045c8df309c3
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qlist.cpp

@@ -584,6 +584,54 @@ void **QListData::erase(void **xi)
     \sa operator==()
 */
 
+/*! \fn bool operator<(const QList<T> &lhs, const QList<T> &rhs)
+    \since 5.6
+    \relates QList
+
+    Returns \c true if list \a lhs is
+    \l{http://en.cppreference.com/w/cpp/algorithm/lexicographical_compare}
+    {lexicographically less than} \a rhs; otherwise returns \c false.
+
+    This function requires the value type to have an implementation
+    of \c operator<().
+*/
+
+/*! \fn bool operator<=(const QList<T> &lhs, const QList<T> &rhs)
+    \since 5.6
+    \relates QList
+
+    Returns \c true if list \a lhs is
+    \l{http://en.cppreference.com/w/cpp/algorithm/lexicographical_compare}
+    {lexicographically less than or equal to} \a rhs; otherwise returns \c false.
+
+    This function requires the value type to have an implementation
+    of \c operator<().
+*/
+
+/*! \fn bool operator>(const QList<T> &lhs, const QList<T> &rhs)
+    \since 5.6
+    \relates QList
+
+    Returns \c true if list \a lhs is
+    \l{http://en.cppreference.com/w/cpp/algorithm/lexicographical_compare}
+    {lexicographically greater than} \a rhs; otherwise returns \c false.
+
+    This function requires the value type to have an implementation
+    of \c operator<().
+*/
+
+/*! \fn bool operator>=(const QList<T> &lhs, const QList<T> &rhs)
+    \since 5.6
+    \relates QList
+
+    Returns \c true if list \a lhs is
+    \l{http://en.cppreference.com/w/cpp/algorithm/lexicographical_compare}
+    {lexicographically greater than or equal to} \a rhs; otherwise returns \c false.
+
+    This function requires the value type to have an implementation
+    of \c operator<().
+*/
+
 /*!
     \fn int QList::size() const
 

src/corelib/tools/qlist.h

@@ -1015,6 +1015,36 @@ inline int QList<T>::count_impl(const T &t, QListData::ArrayCompatibleLayout) co
 Q_DECLARE_SEQUENTIAL_ITERATOR(List)
 Q_DECLARE_MUTABLE_SEQUENTIAL_ITERATOR(List)
 
+template <typename T>
+bool operator<(const QList<T> &lhs, const QList<T> &rhs)
+    Q_DECL_NOEXCEPT_EXPR(noexcept(std::lexicographical_compare(lhs.begin(), lhs.end(),
+                                                               rhs.begin(), rhs.end())))
+{
+    return std::lexicographical_compare(lhs.begin(), lhs.end(),
+                                        rhs.begin(), rhs.end());
+}
+
+template <typename T>
+inline bool operator>(const QList<T> &lhs, const QList<T> &rhs)
+    Q_DECL_NOEXCEPT_EXPR(noexcept(lhs < rhs))
+{
+    return rhs < lhs;
+}
+
+template <typename T>
+inline bool operator<=(const QList<T> &lhs, const QList<T> &rhs)
+    Q_DECL_NOEXCEPT_EXPR(noexcept(lhs < rhs))
+{
+    return !(lhs > rhs);
+}
+
+template <typename T>
+inline bool operator>=(const QList<T> &lhs, const QList<T> &rhs)
+    Q_DECL_NOEXCEPT_EXPR(noexcept(lhs < rhs))
+{
+    return !(lhs < rhs);
+}
+
 QT_END_NAMESPACE
 
 #include <QtCore/qbytearraylist.h>

tests/auto/corelib/tools/qlist/tst_qlist.cpp

@@ -76,6 +76,13 @@ struct Movable {
         return i == other.i;
     }
 
+    bool operator<(const Movable &other) const
+    {
+        check(state, Constructed);
+        check(other.state, Constructed);
+        return i < other.i;
+    }
+
     Movable &operator=(const Movable &other)
     {
         check(state, Constructed);
@@ -144,6 +151,13 @@ struct Optimal
         return i == other.i;
     }
 
+    bool operator<(const Optimal &other) const
+    {
+        check(state, Constructed);
+        check(other.state, Constructed);
+        return i < other.i;
+    }
+
     Optimal &operator=(const Optimal &other)
     {
         check(state, Constructed);
@@ -220,6 +234,12 @@ struct Complex
         return value == other.value;
     }
 
+    bool operator<(Complex const &other) const
+    {
+        check(); other.check();
+        return value < other.value;
+    }
+
     void check() const
     {
         QVERIFY(this == checkSum);
@@ -1576,6 +1596,19 @@ void tst_QList::testOperators() const
     // []
     QCOMPARE(list[0], T_FOO);
     QCOMPARE(list[list.size() - 1], T_CAT);
+
+    // <, >, <=, >=
+    QVERIFY(!(list <  listtwo));
+    QVERIFY(!(list >  listtwo));
+    QVERIFY(  list <= listtwo);
+    QVERIFY(  list >= listtwo);
+    listtwo.push_back(T_CAT);
+    QVERIFY(  list <  listtwo);
+    QVERIFY(!(list >  listtwo));
+    QVERIFY(  list <= listtwo);
+    QVERIFY(!(list >= listtwo));
+    QVERIFY(listtwo >  list);
+    QVERIFY(listtwo >= list);
 }
 
 void tst_QList::testOperatorsOptimal() const