QStringBuilder: add operator += for QString and QByteArray

Optimize cases when we have.
string += someString + someOtherString
Avoid the allocation of one temporary string.

Behaviour change:
byteArray += someString + QByteArray("foo\0bar", 7)
before, the array would end at foo because of the conversion to string

Reviewed-by: hjk

2 files changed, 32 insertions, 0 deletions

diff --git a/src/corelib/tools/qstring.h b/src/corelib/tools/qstring.h
index b54258f..002e516 100644
--- a/src/corelib/tools/qstring.h
+++ b/src/corelib/tools/qstring.h
@@ -485,6 +485,9 @@ public:
     const_iterator constEnd() const;
 
     // STL compatibility
+    typedef const QChar & const_reference;
+    typedef QChar & reference;
+    typedef QChar value_type;
     inline void push_back(QChar c) { append(c); }
     inline void push_back(const QString &s) { append(s); }
     inline void push_front(QChar c) { prepend(c); }
diff --git a/src/corelib/tools/qstringbuilder.h b/src/corelib/tools/qstringbuilder.h
index 260b574..2d3475f 100644
--- a/src/corelib/tools/qstringbuilder.h
+++ b/src/corelib/tools/qstringbuilder.h
@@ -419,6 +419,35 @@ operator+(const A &a, const B &b)
 }
 #endif
 
+template <typename A, typename B>
+QByteArray &operator+=(QByteArray &a, const QStringBuilder<A, B> &b)
+{
+#ifndef QT_NO_CAST_TO_ASCII
+    if (sizeof(typename QConcatenable< QStringBuilder<A, B> >::ConvertTo::value_type) == sizeof(QChar)) {
+        //it is not save to optimize as in utf8 it is not possible to compute the size
+        return a += QString(b);
+    }
+#endif
+    int len = a.size() + QConcatenable< QStringBuilder<A, B> >::size(b);
+    a.reserve(len);
+    char *it = a.data() + a.size();
+    QConcatenable< QStringBuilder<A, B> >::appendTo(b, it);
+    a.resize(len); //we need to resize after the appendTo for the case str+=foo+str
+    return a;
+}
+
+template <typename A, typename B>
+QString &operator+=(QString &a, const QStringBuilder<A, B> &b)
+{
+    int len = a.size() + QConcatenable< QStringBuilder<A, B> >::size(b);
+    a.reserve(len);
+    QChar *it = a.data() + a.size();
+    QConcatenable< QStringBuilder<A, B> >::appendTo(b, it);
+    a.resize(it - a.constData()); //may be smaller than len if there was conversion from utf8
+    return a;
+}
+
+
 QT_END_NAMESPACE
 
 QT_END_HEADER