Make it possible to use QPointer<const T>

This is possible with QWeakPointer, so allow it for migrating
code too.

In the process, replace the QPointerBase with a member variable for
simplicity. The functionality of the QPointerBase is replaced
by a TypeSelector template.

Change-Id: I3b4c77bdeda2b863cc33e84a3da8a25bae928c8c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

dist/changes-5.1.0

@@ -64,6 +64,9 @@ QtCore
       inside the pattern string, as well as the numerical index of each
       named capturing group.
 
+ - QPointer
+    * It is now possible to create a QPointer with a const templated type.
+
  -
 
 QtGui

src/corelib/kernel/qpointer.h

@@ -50,56 +50,44 @@ QT_BEGIN_NAMESPACE
 
 class QVariant;
 
-class QPointerBase
-{
-    QWeakPointer<QObject> wp;
-
-protected:
-    inline QPointerBase() : wp() { }
-    inline QPointerBase(QObject *p) : wp(p, true) { }
-    // compiler-generated copy/move ctor/assignment operators are fine! (even though public)
-    inline ~QPointerBase() { }
-
-    inline QObject* data() const
-    { return wp.data(); }
-
-    inline void assign(QObject *p)
-    { wp.assign(p); }
-
-    inline bool isNull() const
-    { return wp.isNull(); }
-
-    inline void clear()
-    { wp.clear(); }
-};
-
 template <class T>
-class QPointer : private QPointerBase
+class QPointer
 {
+    template<typename U>
+    struct TypeSelector
+    {
+        typedef QObject Type;
+    };
+    template<typename U>
+    struct TypeSelector<const U>
+    {
+        typedef const QObject Type;
+    };
+    typedef typename TypeSelector<T>::Type QObjectType;
+    QWeakPointer<QObjectType> wp;
 public:
     inline QPointer() { }
-    inline QPointer(T *p) : QPointerBase(p) { }
+    inline QPointer(T *p) : wp(p, true) { }
     // compiler-generated copy/move ctor/assignment operators are fine!
     inline ~QPointer() { }
 
     inline QPointer<T> &operator=(T* p)
-    { QPointerBase::assign(p); return *this; }
+    { wp.assign(static_cast<QObjectType*>(p)); return *this; }
 
     inline T* data() const
-    { return static_cast<T*>(QPointerBase::data()); }
+    { return static_cast<T*>( wp.data()); }
     inline T* operator->() const
     { return data(); }
     inline T& operator*() const
     { return *data(); }
     inline operator T*() const
     { return data(); }
-#ifdef Q_QDOC
-    inline bool isNull() const;
-    inline void clear();
-#else
-    using QPointerBase::isNull;
-    using QPointerBase::clear;
-#endif
+
+    inline bool isNull() const
+    { return wp.isNull(); }
+
+    inline void clear()
+    { wp.clear(); }
 };
 template <class T> Q_DECLARE_TYPEINFO_BODY(QPointer<T>, Q_MOVABLE_TYPE);
 

src/corelib/tools/qsharedpointer_impl.h

@@ -639,7 +639,7 @@ private:
 public:
 #else
     template <class X> friend class QSharedPointer;
-    friend class QPointerBase;
+    template <class X> friend class QPointer;
 #endif
 
     template <class X>

tests/auto/corelib/kernel/qpointer/tst_qpointer.cpp

@@ -65,6 +65,7 @@ private slots:
     void threadSafety();
 
     void qvariantCast();
+    void constPointer();
 };
 
 void tst_QPointer::constructors()
@@ -384,6 +385,12 @@ void tst_QPointer::qvariantCast()
 //     QPointer<int> sop = qPointerFromVariant<int>(v);
 }
 
+void tst_QPointer::constPointer()
+{
+    // Compile-time test that QPointer<const T> works.
+    QPointer<const QFile> fp = new QFile;
+    delete fp.data();
+}
 
 
 QTEST_MAIN(tst_QPointer)