QStringList: add op= overloads for QList<QString>

QStringList = QList<QString> already compiled, but was interpreted as
QStringList = QStringList(QList<QString>), which involves the QList
copy ctor. Adding the overload saves that copy.

Cannot use a using declaration here, since the return type is different.

Change-Id: I9f4feb2f97480d2d6a3b6fa7c71b5d511b623601
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qstringlist.cpp

@@ -203,6 +203,27 @@ QT_BEGIN_NAMESPACE
     \sa operator=()
 */
 
+/*!
+    \fn QStringList &QStringList::operator=(const QList<QString> &other)
+    \since 5.4
+
+    Copy assignment operator from QList<QString>. Assigns the \a other
+    list of strings to this string list.
+
+    After the operation, \a other and \c *this will be equal.
+*/
+
+/*!
+    \fn QStringList &QStringList::operator=(QList<QString> &&other)
+    \overload
+    \since 5.4
+
+    Move assignment operator from QList<QString>. Moves the \a other
+    list of strings to this string list.
+
+    After the operation, \a other will be empty.
+*/
+
 /*!
     \fn void QStringList::sort(Qt::CaseSensitivity cs)
 

src/corelib/tools/qstringlist.h

@@ -68,6 +68,13 @@ public:
     inline QStringList(std::initializer_list<QString> args) : QList<QString>(args) { }
 #endif
 
+    QStringList &operator=(const QList<QString> &other)
+    { QList<QString>::operator=(other); return *this; }
+#ifdef Q_COMPILER_RVALUE_REFS
+    QStringList &operator=(QList<QString> &&other)
+    { QList<QString>::operator=(std::move(other)); return *this; }
+#endif
+
     inline void sort(Qt::CaseSensitivity cs = Qt::CaseSensitive);
     inline int removeDuplicates();
 

tests/auto/corelib/tools/qstringlist/tst_qstringlist.cpp

@@ -66,6 +66,7 @@ private slots:
     void lastIndexOf_regExp();
 
     void streamingOperator();
+    void assignmentOperator();
     void join() const;
     void join_data() const;
     void joinEmptiness() const;
@@ -344,6 +345,21 @@ void tst_QStringList::streamingOperator()
     QCOMPARE(list2 << list3, QStringList() << "adam" << "eva");
 }
 
+void tst_QStringList::assignmentOperator()
+{
+    // compile-only test
+
+    QStringList adam;
+    adam << "adam";
+    QList<QString> eva;
+    eva << "eva";
+    QStringList result;
+    QStringList &ref1 = (result = adam);
+    QStringList &ref2 = (result = eva);
+    Q_UNUSED(ref1);
+    Q_UNUSED(ref2);
+}
+
 void tst_QStringList::join() const
 {
     QFETCH(QStringList, input);