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

std::vector has them, too.

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

Change-Id: I0bcb22dfcc43cb0362f17b4e06154ce18646580a
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qvector.cpp

@@ -290,6 +290,54 @@
     \sa operator==()
 */
 
+/*! \fn bool operator<(const QVector<T> &lhs, const QVector<T> &rhs)
+    \since 5.6
+    \relates QVector
+
+    Returns \c true if vector \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 QVector<T> &lhs, const QVector<T> &rhs)
+    \since 5.6
+    \relates QVector
+
+    Returns \c true if vector \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 QVector<T> &lhs, const QVector<T> &rhs)
+    \since 5.6
+    \relates QVector
+
+    Returns \c true if vector \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 QVector<T> &lhs, const QVector<T> &rhs)
+    \since 5.6
+    \relates QVector
+
+    Returns \c true if vector \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 QVector::size() const
 
     Returns the number of items in the vector.

src/corelib/tools/qvector.h

@@ -865,6 +865,36 @@ QList<T> QList<T>::fromVector(const QVector<T> &vector)
 Q_DECLARE_SEQUENTIAL_ITERATOR(Vector)
 Q_DECLARE_MUTABLE_SEQUENTIAL_ITERATOR(Vector)
 
+template <typename T>
+bool operator<(const QVector<T> &lhs, const QVector<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 QVector<T> &lhs, const QVector<T> &rhs)
+    Q_DECL_NOEXCEPT_EXPR(noexcept(lhs < rhs))
+{
+    return rhs < lhs;
+}
+
+template <typename T>
+inline bool operator<=(const QVector<T> &lhs, const QVector<T> &rhs)
+    Q_DECL_NOEXCEPT_EXPR(noexcept(lhs < rhs))
+{
+    return !(lhs > rhs);
+}
+
+template <typename T>
+inline bool operator>=(const QVector<T> &lhs, const QVector<T> &rhs)
+    Q_DECL_NOEXCEPT_EXPR(noexcept(lhs < rhs))
+{
+    return !(lhs < rhs);
+}
+
 /*
    ### Qt 5:
    ### This needs to be removed for next releases of Qt. It is a workaround for vc++ because

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

@@ -123,6 +123,13 @@ struct Custom {
         return i == other.i;
     }
 
+    bool operator<(const Custom &other) const
+    {
+        check(&other);
+        check(this);
+        return i < other.i;
+    }
+
     Custom &operator=(const Custom &other)
     {
         check(&other);
@@ -2076,6 +2083,19 @@ void tst_QVector::testOperators() const
     // ==
     QVERIFY(myvec == combined);
 
+    // <, >, <=, >=
+    QVERIFY(!(myvec <  combined));
+    QVERIFY(!(myvec >  combined));
+    QVERIFY(  myvec <= combined);
+    QVERIFY(  myvec >= combined);
+    combined.push_back("G");
+    QVERIFY(  myvec <  combined);
+    QVERIFY(!(myvec >  combined));
+    QVERIFY(  myvec <= combined);
+    QVERIFY(!(myvec >= combined));
+    QVERIFY(combined >  myvec);
+    QVERIFY(combined >= myvec);
+
     // []
     QCOMPARE(myvec[0], QLatin1String("A"));
     QCOMPARE(myvec[1], QLatin1String("B"));