Add qobject_cast for QSharedPointer.

This obviously only works for classes that derive from QObject. And
you must remember that QSharedPointer controls the QObject's lifetime,
not the QObject parent-child relationship.

Reviewed-by: dt
Reviewed-by: Bradley T. Hughes

4 files changed, 233 insertions, 0 deletions

diff --git a/src/corelib/tools/qsharedpointer.cpp b/src/corelib/tools/qsharedpointer.cpp
index ba62ce1..71bf318 100644
--- a/src/corelib/tools/qsharedpointer.cpp
+++ b/src/corelib/tools/qsharedpointer.cpp
@@ -340,6 +340,23 @@
 */
 
 /*!
+    \fn QSharedPointer<X> QSharedPointer::objectCast() const
+
+    Performs a \ref qobject_cast from this pointer's type to \tt X and
+    returns a QSharedPointer that shares the reference. If this
+    function is used to up-cast, then QSharedPointer will perform a \tt
+    qobject_cast, which means that if the object being pointed by this
+    QSharedPointer is not of type \tt X, the returned object will be
+    null.
+
+    Note: the template type \c X must have the same const and volatile
+    qualifiers as the template of this object, or the cast will
+    fail. Use constCast() if you need to drop those qualifiers.
+
+    \sa qSharedPointerObjectCast()
+*/
+
+/*!
     \fn QWeakPointer<T> QSharedPointer::toWeakRef() const
 
     Returns a weak reference object that shares the pointer referenced
@@ -718,6 +735,45 @@
 */
 
 /*!
+    \fn QSharedPointer<X> qSharedPointerObjectCast(const QSharedPointer<T> &other)
+    \relates QSharedPointer
+
+    Returns a shared pointer to the pointer held by \a other, using a
+    \ref qobject_cast to type \tt X to obtain an internal pointer of the
+    appropriate type. If the \tt qobject_cast fails, the object
+    returned will be null.
+
+    Note that \tt X must have the same cv-qualifiers (\tt const and
+    \tt volatile) that \tt T has, or the code will fail to
+    compile. Use qSharedPointerConstCast to cast away the constness.
+
+    \sa QSharedPointer::objectCast(), qSharedPointerCast(), qSharedPointerConstCast()
+*/
+
+/*!
+    \fn QSharedPointer<X> qSharedPointerObjectCast(const QWeakPointer<T> &other)
+    \relates QSharedPointer
+    \relates QWeakPointer
+
+    Returns a shared pointer to the pointer held by \a other, using a
+    \ref qobject_cast to type \tt X to obtain an internal pointer of the
+    appropriate type. If the \tt qobject_cast fails, the object
+    returned will be null.
+
+    The \a other object is converted first to a strong reference. If
+    that conversion fails (because the object it's pointing to has
+    already been deleted), this function also returns a null
+    QSharedPointer.
+
+    Note that \tt X must have the same cv-qualifiers (\tt const and
+    \tt volatile) that \tt T has, or the code will fail to
+    compile. Use qSharedPointerConstCast to cast away the constness.
+
+    \sa QWeakPointer::toStrongRef(), qSharedPointerCast(), qSharedPointerConstCast()
+*/
+
+
+/*!
     \fn QWeakPointer<X> qWeakPointerCast(const QWeakPointer<T> &other)
     \relates QWeakPointer
 
diff --git a/src/corelib/tools/qsharedpointer.h b/src/corelib/tools/qsharedpointer.h
index cd6bc62..abd83ad 100644
--- a/src/corelib/tools/qsharedpointer.h
+++ b/src/corelib/tools/qsharedpointer.h
@@ -93,6 +93,7 @@ public:
     template <class X> QSharedPointer<X> staticCast() const;
     template <class X> QSharedPointer<X> dynamicCast() const;
     template <class X> QSharedPointer<X> constCast() const;
+    template <class X> QSharedPointer<X> objectCast() const;
 };
 
 template <class T>
@@ -136,6 +137,8 @@ template <class X, class T> QSharedPointer<X> qSharedPointerDynamicCast(const QS
 template <class X, class T> QSharedPointer<X> qSharedPointerDynamicCast(const QWeakPointer<T> &src);
 template <class X, class T> QSharedPointer<X> qSharedPointerConstCast(const QSharedPointer<T> &src);
 template <class X, class T> QSharedPointer<X> qSharedPointerConstCast(const QWeakPointer<T> &src);
+template <class X, class T> QSharedPointer<X> qSharedPointerObjectCast(const QSharedPointer<T> &src);
+template <class X, class T> QSharedPointer<X> qSharedPointerObjectCast(const QWeakPointer<T> &src);
 
 template <class X, class T> QWeakPointer<X> qWeakPointerCast(const QWeakPointer<T> &src);
 
diff --git a/src/corelib/tools/qsharedpointer_impl.h b/src/corelib/tools/qsharedpointer_impl.h
index 2797622..df31fec 100644
--- a/src/corelib/tools/qsharedpointer_impl.h
+++ b/src/corelib/tools/qsharedpointer_impl.h
@@ -49,6 +49,7 @@
 #endif
 
 #include <QtCore/qatomic.h>
+#include <QtCore/qobject.h>    // for qobject_cast
 
 QT_BEGIN_HEADER
 
@@ -83,6 +84,11 @@ QSharedPointer<X> qSharedPointerDynamicCast(const QSharedPointer<T> &ptr);
 template <class X, class T>
 QSharedPointer<X> qSharedPointerConstCast(const QSharedPointer<T> &ptr);
 
+#ifndef QT_NO_QOBJECT
+template <class X, class T>
+QSharedPointer<X> qSharedPointerObjectCast(const QSharedPointer<T> &ptr);
+#endif
+
 namespace QtSharedPointer {
     template <class T> class InternalRefCount;
     template <class T> class ExternalRefCount;
@@ -330,6 +336,14 @@ public:
         return qSharedPointerConstCast<X, T>(*this);
     }
 
+#ifndef QT_NO_QOBJECT
+    template <class X>
+    QSharedPointer<X> objectCast() const
+    {
+        return qSharedPointerObjectCast<X, T>(*this);
+    }
+#endif
+
     inline void clear() { *this = QSharedPointer<T>(); }
 
     QWeakPointer<T> toWeakRef() const;
@@ -545,6 +559,43 @@ QWeakPointer<X> qWeakPointerCast(const QSharedPointer<T> &src)
     return qSharedPointerCast<X, T>(src).toWeakRef();
 }
 
+#ifndef QT_NO_QOBJECT
+template <class X, class T>
+Q_INLINE_TEMPLATE QSharedPointer<X> qSharedPointerObjectCast(const QSharedPointer<T> &src)
+{
+    register X *ptr = qobject_cast<X *>(src.data());
+    return QtSharedPointer::copyAndSetPointer(ptr, src);
+}
+template <class X, class T>
+Q_INLINE_TEMPLATE QSharedPointer<X> qSharedPointerObjectCast(const QWeakPointer<T> &src)
+{
+    return qSharedPointerObjectCast<X>(src.toStrongRef());
+}
+
+# ifndef QT_NO_PARTIAL_TEMPLATE_SPECIALIZATION
+namespace QtSharedPointer {
+    template <class T> struct RemovePointer;
+    template <class T> struct RemovePointer<T *> { typedef T Type; };
+    template <class T> struct RemovePointer<QSharedPointer<T> > { typedef T Type; };
+    template <class T> struct RemovePointer<QWeakPointer<T> > { typedef T Type; };
+}
+
+template <class X, class T>
+inline QSharedPointer<typename QtSharedPointer::RemovePointer<X>::Type>
+qobject_cast(const QSharedPointer<T> &src)
+{
+    return qSharedPointerObjectCast<typename QtSharedPointer::RemovePointer<X>::Type, T>(src);
+}
+template <class X, class T>
+inline QSharedPointer<typename QtSharedPointer::RemovePointer<X>::Type>
+qobject_cast(const QWeakPointer<T> &src)
+{
+    return qSharedPointerObjectCast<typename QtSharedPointer::RemovePointer<X>::Type, T>(src);
+}
+# endif
+
+#endif
+
 QT_END_NAMESPACE
 
 QT_END_HEADER
diff --git a/tests/auto/qsharedpointer/tst_qsharedpointer.cpp b/tests/auto/qsharedpointer/tst_qsharedpointer.cpp
index db93fc9..57ebdce 100644
--- a/tests/auto/qsharedpointer/tst_qsharedpointer.cpp
+++ b/tests/auto/qsharedpointer/tst_qsharedpointer.cpp
@@ -56,6 +56,7 @@ private slots:
     void memoryManagement();
     void downCast();
     void upCast();
+    void objectCast();
     void differentPointers();
     void virtualBaseDifferentPointers();
 #ifndef QTEST_NO_RTTI
@@ -424,6 +425,109 @@ void tst_QSharedPointer::upCast()
     QCOMPARE(int(baseptr.d->strongref), 1);
 }
 
+class OtherObject: public QObject
+{
+    Q_OBJECT
+};
+
+void tst_QSharedPointer::objectCast()
+{
+    {
+        OtherObject *data = new OtherObject;
+        QSharedPointer<QObject> baseptr = QSharedPointer<QObject>(data);
+        QVERIFY(baseptr == data);
+        QVERIFY(data == baseptr);
+
+        // perform object cast
+        QSharedPointer<OtherObject> ptr = qSharedPointerObjectCast<OtherObject>(baseptr);
+        QVERIFY(!ptr.isNull());
+        QCOMPARE(ptr.data(), data);
+        QVERIFY(ptr == data);
+
+        // again:
+        ptr = baseptr.objectCast<OtherObject>();
+        QVERIFY(ptr == data);
+
+#ifndef QT_NO_PARTIAL_TEMPLATE_SPECIALIZATION
+        // again:
+        ptr = qobject_cast<OtherObject *>(baseptr);
+        QVERIFY(ptr == data);
+
+        // again:
+        ptr = qobject_cast<QSharedPointer<OtherObject> >(baseptr);
+        QVERIFY(ptr == data);
+#endif
+    }
+
+    {
+        const OtherObject *data = new OtherObject;
+        QSharedPointer<const QObject> baseptr = QSharedPointer<const QObject>(data);
+        QVERIFY(baseptr == data);
+        QVERIFY(data == baseptr);
+
+        // perform object cast
+        QSharedPointer<const OtherObject> ptr = qSharedPointerObjectCast<const OtherObject>(baseptr);
+        QVERIFY(!ptr.isNull());
+        QCOMPARE(ptr.data(), data);
+        QVERIFY(ptr == data);
+
+        // again:
+        ptr = baseptr.objectCast<const OtherObject>();
+        QVERIFY(ptr == data);
+
+#ifndef QT_NO_PARTIAL_TEMPLATE_SPECIALIZATION
+        // again:
+        ptr = qobject_cast<const OtherObject *>(baseptr);
+        QVERIFY(ptr == data);
+
+        // again:
+        ptr = qobject_cast<QSharedPointer<const OtherObject> >(baseptr);
+        QVERIFY(ptr == data);
+#endif
+    }
+
+    {
+        OtherObject *data = new OtherObject;
+        QPointer<OtherObject> qptr = data;
+        QSharedPointer<OtherObject> ptr = QSharedPointer<OtherObject>(data);
+        QWeakPointer<QObject> weakptr = ptr;
+
+        {
+            // perform object cast
+            QSharedPointer<OtherObject> otherptr = qSharedPointerObjectCast<OtherObject>(weakptr);
+            QVERIFY(otherptr == ptr);
+
+            // again:
+            otherptr = qobject_cast<OtherObject *>(weakptr);
+            QVERIFY(otherptr == ptr);
+
+            // again:
+            otherptr = qobject_cast<QSharedPointer<OtherObject> >(weakptr);
+            QVERIFY(otherptr == ptr);
+        }
+
+        // drop the reference:
+        ptr.clear();
+        QVERIFY(ptr.isNull());
+        QVERIFY(qptr.isNull());
+        QVERIFY(weakptr.toStrongRef().isNull());
+
+        // verify that the object casts fail without crash
+        QSharedPointer<OtherObject> otherptr = qSharedPointerObjectCast<OtherObject>(weakptr);
+        QVERIFY(otherptr.isNull());
+
+#ifndef QT_NO_PARTIAL_TEMPLATE_SPECIALIZATION
+        // again:
+        otherptr = qobject_cast<OtherObject *>(weakptr);
+        QVERIFY(otherptr.isNull());
+
+        // again:
+        otherptr = qobject_cast<QSharedPointer<OtherObject> >(weakptr);
+        QVERIFY(otherptr.isNull());
+#endif
+    }
+}
+
 void tst_QSharedPointer::differentPointers()
 {
     {
@@ -939,6 +1043,20 @@ void tst_QSharedPointer::invalidConstructs_data()
         << "QSharedPointer<const Data> baseptr = QSharedPointer<const Data>(new Data);\n"
            "QSharedPointer<Data> ptr;"
            "ptr = baseptr;";
+    QTest::newRow("const-dropping-static-cast")
+        << &QTest::QExternalTest::tryCompileFail
+        << "QSharedPointer<const Data> baseptr = QSharedPointer<const Data>(new Data);\n"
+        "qSharedPointerCast<DerivedData>(baseptr);";
+#ifndef QTEST_NO_RTTI
+    QTest::newRow("const-dropping-dynamic-cast")
+        << &QTest::QExternalTest::tryCompileFail
+        << "QSharedPointer<const Data> baseptr = QSharedPointer<const Data>(new Data);\n"
+        "qSharedPointerDynamicCast<DerivedData>(baseptr);";
+#endif
+    QTest::newRow("const-dropping-object-cast")
+        << &QTest::QExternalTest::tryCompileFail
+        << "QSharedPointer<const QObject> baseptr = QSharedPointer<const QObject>(new QObject);\n"
+        "qSharedPointerObjectCast<QCoreApplication>(baseptr);";
 
     // arithmethics through automatic cast operators
     QTest::newRow("arithmethic1")
@@ -982,6 +1100,10 @@ void tst_QSharedPointer::invalidConstructs_data()
         << &QTest::QExternalTest::tryCompileFail
         << "QSharedPointer<Data> ptr1;\n"
            "QSharedPointer<int> ptr2 = qSharedPointerConstCast<int>(ptr1);";
+    QTest::newRow("invalid-cast4")
+        << &QTest::QExternalTest::tryCompileFail
+        << "QSharedPointer<Data> ptr1;\n"
+           "QSharedPointer<int> ptr2 = qSharedPointerObjectCast<int>(ptr1);";
 }
 
 void tst_QSharedPointer::invalidConstructs()
@@ -999,6 +1121,7 @@ void tst_QSharedPointer::invalidConstructs()
     test.setProgramHeader(
         "#define QT_SHAREDPOINTER_TRACK_POINTERS\n"
         "#include <QtCore/qsharedpointer.h>\n"
+        "#include <QtCore/qcoreapplication.h>\n"
         "\n"
         "struct Data { int i; };\n"
         "struct DerivedData: public Data { int j; };\n"