QString: where possible, re-use existing capacity in op(QChar/QL1S)

If the LHS is detached and has existing capacity that is large
enough to hold the RHS, re-use the memory instead of allocating
a new buffer and throwing away the old.

Change-Id: I53d42825da92c264c7301e8e771cba9fb35c321b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/tests/auto/corelib/tools/qstring/tst_qstring.cpp b/tests/auto/corelib/tools/qstring/tst_qstring.cpp
index cc9f250be9..907dcf17e1 100644
--- a/tests/auto/corelib/tools/qstring/tst_qstring.cpp
+++ b/tests/auto/corelib/tools/qstring/tst_qstring.cpp
@@ -582,6 +582,7 @@ private slots:
     void compareQLatin1Strings();
     void fromQLatin1StringWithLength();
     void assignQLatin1String();
+    void assignQChar();
     void isRightToLeft_data();
     void isRightToLeft();
     void unicodeStrings();
@@ -6598,6 +6599,71 @@ void tst_QString::assignQLatin1String()
     QCOMPARE(foo.size(), latin1subfoo.size());
     QCOMPARE(foo, QString::fromLatin1("foo"));
 
+    // check capacity re-use:
+    QString s;
+    QCOMPARE(s.capacity(), 0);
+
+    // assign to null QString:
+    s = latin1foo;
+    QCOMPARE(s, QString::fromLatin1("foo"));
+    QCOMPARE(s.capacity(), 3);
+
+    // assign to non-null QString with enough capacity:
+    s = QString::fromLatin1("foofoo");
+    const int capacity = s.capacity();
+    s = latin1foo;
+    QCOMPARE(s, QString::fromLatin1("foo"));
+    QCOMPARE(s.capacity(), capacity);
+
+    // assign to shared QString (enough capacity, but can't use):
+    s = QString::fromLatin1("foofoo");
+    QString s2 = s;
+    s = latin1foo;
+    QCOMPARE(s, QString::fromLatin1("foo"));
+    QCOMPARE(s.capacity(), 3);
+
+    // assign to QString with too little capacity:
+    s = QString::fromLatin1("fo");
+    QCOMPARE(s.capacity(), 2);
+    s = latin1foo;
+    QCOMPARE(s, QString::fromLatin1("foo"));
+    QCOMPARE(s.capacity(), 3);
+
+}
+
+void tst_QString::assignQChar()
+{
+    const QChar sp = QLatin1Char(' ');
+    QString s;
+    QCOMPARE(s.capacity(), 0);
+
+    // assign to null QString:
+    s = sp;
+    QCOMPARE(s, QString(sp));
+    QCOMPARE(s.capacity(), 1);
+
+    // assign to non-null QString with enough capacity:
+    s = QLatin1String("foo");
+    const int capacity = s.capacity();
+    QCOMPARE(capacity, 3);
+    s = sp;
+    QCOMPARE(s, QString(sp));
+    QCOMPARE(s.capacity(), capacity);
+
+    // assign to shared QString (enough capacity, but can't use):
+    s = QLatin1String("foo");
+    QString s2 = s;
+    s = sp;
+    QCOMPARE(s, QString(sp));
+    QCOMPARE(s.capacity(), 1);
+
+    // assign to empty QString:
+    s = QString("");
+    s.detach();
+    QCOMPARE(s.capacity(), 0);
+    s = sp;
+    QCOMPARE(s, QString(sp));
+    QCOMPARE(s.capacity(), 1);
 }
 
 void tst_QString::isRightToLeft_data()