QStringList::join: add an overload taking a single QChar

This overload avoids the needless heap allocation that the traditional
overload incurs due to the implicit QChar -> QString conversion
involved there.

In order to share the implementation between the two overloads,
QStringList_join now takes the separator as a (Char*,int) tuple
instead of as a QString.

Change-Id: I92961f13a3f19099de2a6e2df9f4789a12fc83a0
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qstringlist.cpp

@@ -434,7 +434,13 @@ void QtPrivate::QStringList_replaceInStrings(QStringList *that, const QRegularEx
 
     \sa QString::split()
 */
-QString QtPrivate::QStringList_join(const QStringList *that, const QString &sep)
+
+/*!
+    \fn QString QStringList::join(QChar separator) const
+    \since 5.0
+    \overload join()
+*/
+QString QtPrivate::QStringList_join(const QStringList *that, const QChar *sep, int seplen)
 {
     int totalLength = 0;
     const int size = that->size();
@@ -443,7 +449,7 @@ QString QtPrivate::QStringList_join(const QStringList *that, const QString &sep)
         totalLength += that->at(i).size();
 
     if(size > 0)
-        totalLength += sep.size() * (size - 1);
+        totalLength += seplen * (size - 1);
 
     QString res;
     if (totalLength == 0)
@@ -451,7 +457,7 @@ QString QtPrivate::QStringList_join(const QStringList *that, const QString &sep)
     res.reserve(totalLength);
     for (int i = 0; i < that->size(); ++i) {
         if (i)
-            res += sep;
+            res.append(sep, seplen);
         res += that->at(i);
     }
     return res;

src/corelib/tools/qstringlist.h

@@ -75,6 +75,7 @@ public:
     inline int removeDuplicates();
 
     inline QString join(const QString &sep) const;
+    inline QString join(QChar sep) const;
 
     inline QStringList filter(const QString &str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const;
     inline bool contains(const QString &str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const;
@@ -122,7 +123,7 @@ Q_DECLARE_TYPEINFO(QStringList, Q_MOVABLE_TYPE);
 namespace QtPrivate {
     void Q_CORE_EXPORT QStringList_sort(QStringList *that, Qt::CaseSensitivity cs);
     int Q_CORE_EXPORT QStringList_removeDuplicates(QStringList *that);
-    QString Q_CORE_EXPORT QStringList_join(const QStringList *that, const QString &sep);
+    QString Q_CORE_EXPORT QStringList_join(const QStringList *that, const QChar *sep, int seplen);
     QStringList Q_CORE_EXPORT QStringList_filter(const QStringList *that, const QString &str,
                                                Qt::CaseSensitivity cs);
 
@@ -161,7 +162,12 @@ inline int QStringList::removeDuplicates()
 
 inline QString QStringList::join(const QString &sep) const
 {
-    return QtPrivate::QStringList_join(this, sep);
+    return QtPrivate::QStringList_join(this, sep.constData(), sep.length());
+}
+
+inline QString QStringList::join(QChar sep) const
+{
+    return QtPrivate::QStringList_join(this, &sep, 1);
 }
 
 inline QStringList QStringList::filter(const QString &str, Qt::CaseSensitivity cs) const

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

@@ -66,6 +66,8 @@ private slots:
     void join() const;
     void join_data() const;
     void joinEmptiness() const;
+    void joinChar() const;
+    void joinChar_data() const;
 
     void initializeList() const;
 };
@@ -362,6 +364,42 @@ void tst_QStringList::join_data() const
                 << QString("a b c");
 }
 
+void tst_QStringList::joinChar() const
+{
+    QFETCH(QStringList, input);
+    QFETCH(QChar, separator);
+    QFETCH(QString, expectedResult);
+
+    QCOMPARE(input.join(separator), expectedResult);
+}
+
+void tst_QStringList::joinChar_data() const
+{
+    QTest::addColumn<QStringList>("input");
+    QTest::addColumn<QChar>("separator");
+    QTest::addColumn<QString>("expectedResult");
+
+    QTest::newRow("data1")
+                << QStringList()
+                << QChar(QLatin1Char(' '))
+                << QString();
+
+    QTest::newRow("data5")
+                << (QStringList()
+                        << QLatin1String("a")
+                        << QLatin1String("b"))
+                << QChar(QLatin1Char(' '))
+                << QString("a b");
+
+    QTest::newRow("data6")
+                << (QStringList()
+                        << QLatin1String("a")
+                        << QLatin1String("b")
+                        << QLatin1String("c"))
+                << QChar(QLatin1Char(' '))
+                << QString("a b c");
+}
+
 void tst_QStringList::joinEmptiness() const
 {
     QStringList list;