Add support for multiple arguments to QSharedPointer::create()

Requires C++11 rvalue references and variadic templates so we can
implement perfect forwarding.

Change-Id: I62e47d1ffd0c61e8386f9f246aa79031b7430b46
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/corelib/tools/qsharedpointer.cpp

@@ -604,6 +604,37 @@
     \sa qSharedPointerObjectCast()
 */
 
+/*!
+    \fn QSharedPointer<T> QSharedPointer::create()
+    \since 4.6
+
+    Creates a QSharedPointer object and allocates a new item of type \tt T. The
+    QSharedPointer internals and the object are allocated in one single memory
+    allocation, which could help reduce memory fragmentation in a long-running
+    application.
+
+    This function calls the default constructor for type \tt T.
+*/
+
+/*!
+    \fn QSharedPointer<T> QSharedPointer::create(...)
+    \overload
+    \since 5.1
+
+    Creates a QSharedPointer object and allocates a new item of type \tt T. The
+    QSharedPointer internals and the object are allocated in one single memory
+    allocation, which could help reduce memory fragmentation in a long-running
+    application.
+
+    This function will attempt to call a constructor for type \tt T that can
+    accept all the arguments passed. Arguments will be perfectly-forwarded.
+
+    \note This function is only available with a C++11 compiler that supports
+    perfect forwarding of an arbitrary number of arguments. If the compiler
+    does not support the necessary C++11 features, you must use the overload
+    that calls the default constructor.
+*/
+
 /*!
     \fn QWeakPointer<T> QSharedPointer::toWeakRef() const
 

src/corelib/tools/qsharedpointer.h

@@ -95,6 +95,9 @@ public:
     template <class X> QSharedPointer<X> dynamicCast() const;
     template <class X> QSharedPointer<X> constCast() const;
     template <class X> QSharedPointer<X> objectCast() const;
+
+    static inline QSharedPointer<T> create();
+    static inline QSharedPointer<T> create(...);
 };
 
 template <class T>

src/corelib/tools/qsharedpointer_impl.h

@@ -62,6 +62,10 @@ QT_END_HEADER
 #include <QtCore/qobject.h>    // for qobject_cast
 #include <QtCore/qhash.h>    // for qHash
 
+#if defined(Q_COMPILER_RVALUE_REFS) && defined(Q_COMPILER_VARIADIC_TEMPLATES)
+#  include <utility>           // for std::forward
+#endif
+
 QT_BEGIN_HEADER
 
 QT_BEGIN_NAMESPACE
@@ -389,6 +393,28 @@ public:
 
     QWeakPointer<T> toWeakRef() const;
 
+#if defined(Q_COMPILER_RVALUE_REFS) && defined(Q_COMPILER_VARIADIC_TEMPLATES)
+    template <typename... Args>
+    static QSharedPointer<T> create(Args && ...arguments)
+    {
+        typedef QtSharedPointer::ExternalRefCountWithContiguousData<T> Private;
+# ifdef QT_SHAREDPOINTER_TRACK_POINTERS
+        typename Private::DestroyerFn destroy = &Private::safetyCheckDeleter;
+# else
+        typename Private::DestroyerFn destroy = &Private::deleter;
+# endif
+        QSharedPointer<T> result(Qt::Uninitialized);
+        result.d = Private::create(&result.value, destroy);
+
+        // now initialize the data
+        new (result.data()) T(std::forward<Args>(arguments)...);
+        result.d->setQObjectShared(result.value, true);
+# ifdef QT_SHAREDPOINTER_TRACK_POINTERS
+        internalSafetyCheckAdd(result.d, result.value);
+# endif
+        return result;
+    }
+#else
     static inline QSharedPointer<T> create()
     {
         typedef QtSharedPointer::ExternalRefCountWithContiguousData<T> Private;
@@ -408,6 +434,7 @@ public:
         result.d->setQObjectShared(result.value, true);
         return result;
     }
+#endif
 
 private:
     explicit QSharedPointer(Qt::Initialization) {}

tests/auto/corelib/tools/qsharedpointer/tst_qsharedpointer.cpp

@@ -95,6 +95,7 @@ private slots:
     void lambdaCustomDeleter();
 #endif
     void creating();
+    void creatingVariadic();
     void creatingQObject();
     void mixTrackingPointerCode();
     void reentrancyWhileDestructing();
@@ -174,6 +175,49 @@ public:
 int Data::generationCounter = 0;
 int Data::destructorCounter = 0;
 
+struct NoDefaultConstructor1
+{
+    int i;
+    NoDefaultConstructor1(int i) : i(i) {}
+    NoDefaultConstructor1(uint j) : i(j + 42) {}
+};
+
+struct NoDefaultConstructorRef1
+{
+    int &i;
+    NoDefaultConstructorRef1(int &i) : i(i) {}
+};
+
+struct NoDefaultConstructor2
+{
+    void *ptr;
+    int i;
+    NoDefaultConstructor2(void *ptr, int i) : ptr(ptr), i(i) {}
+};
+
+struct NoDefaultConstructorRef2
+{
+    QString str;
+    int i;
+    NoDefaultConstructorRef2(QString &str, int i) : str(str), i(i) {}
+};
+
+struct NoDefaultConstructorConstRef2
+{
+    QString str;
+    int i;
+    NoDefaultConstructorConstRef2(const QString &str, int i) : str(str), i(i) {}
+    NoDefaultConstructorConstRef2(const QByteArray &ba, int i = 42) : str(QString::fromLatin1(ba)), i(i) {}
+};
+
+#ifdef Q_COMPILER_RVALUE_REFS
+struct NoDefaultConstructorRRef1
+{
+    int &i;
+    NoDefaultConstructorRRef1(int &&i) : i(i) {}
+};
+#endif
+
 void tst_QSharedPointer::basics_data()
 {
     QTest::addColumn<bool>("isNull");
@@ -1429,6 +1473,82 @@ void tst_QSharedPointer::creating()
     safetyCheck();
 }
 
+void tst_QSharedPointer::creatingVariadic()
+{
+#if !defined(Q_COMPILER_RVALUE_REFS) || !defined(Q_COMPILER_VARIADIC_TEMPLATES)
+    QSKIP("This compiler is not in C++11 mode or it doesn't support rvalue refs and variadic templates");
+#else
+    int i = 42;
+
+    {
+        NoDefaultConstructor1(1); // control check
+        QSharedPointer<NoDefaultConstructor1> ptr = QSharedPointer<NoDefaultConstructor1>::create(1);
+        QCOMPARE(ptr->i, 1);
+
+        NoDefaultConstructor1(0u); // control check
+        ptr = QSharedPointer<NoDefaultConstructor1>::create(0u);
+        QCOMPARE(ptr->i, 42);
+
+        NoDefaultConstructor1 x(i); // control check
+        ptr = QSharedPointer<NoDefaultConstructor1>::create(i);
+        QCOMPARE(ptr->i, i);
+    }
+    {
+        NoDefaultConstructor2((void*)0, 1); // control check
+        QSharedPointer<NoDefaultConstructor2> ptr = QSharedPointer<NoDefaultConstructor2>::create((void*)0, 1);
+        QCOMPARE(ptr->i, 1);
+        QCOMPARE(ptr->ptr, (void*)0);
+
+        int *null = 0;
+        NoDefaultConstructor2(null, 2); // control check
+        ptr = QSharedPointer<NoDefaultConstructor2>::create(null, 2);
+        QCOMPARE(ptr->i, 2);
+        QCOMPARE(ptr->ptr, (void*)0);
+
+#ifdef Q_COMPILER_NULLPTR
+        NoDefaultConstructor2(nullptr, 3); // control check
+        ptr = QSharedPointer<NoDefaultConstructor2>::create(nullptr, 3);
+        QCOMPARE(ptr->i, 3);
+        QCOMPARE(ptr->ptr, (void*)nullptr);
+#endif
+    }
+    {
+        NoDefaultConstructorRef1 x(i); // control check
+        QSharedPointer<NoDefaultConstructorRef1> ptr = QSharedPointer<NoDefaultConstructorRef1>::create(i);
+        QCOMPARE(ptr->i, i);
+        QCOMPARE(&ptr->i, &i);
+    }
+    {
+        NoDefaultConstructorRRef1(1); // control check
+        QSharedPointer<NoDefaultConstructorRRef1> ptr = QSharedPointer<NoDefaultConstructorRRef1>::create(1);
+        QCOMPARE(ptr->i, 1);
+
+        NoDefaultConstructorRRef1(std::move(i)); // control check
+        ptr = QSharedPointer<NoDefaultConstructorRRef1>::create(std::move(i));
+        QCOMPARE(ptr->i, i);
+    }
+    {
+        QString text("Hello, World");
+        NoDefaultConstructorRef2(text, 1); // control check
+        QSharedPointer<NoDefaultConstructorRef2> ptr = QSharedPointer<NoDefaultConstructorRef2>::create(text, 1);
+        QCOMPARE(ptr->str, text);
+        QCOMPARE(ptr->i, 1);
+    }
+    {
+        QSharedPointer<NoDefaultConstructorConstRef2> ptr;
+        NoDefaultConstructorConstRef2(QLatin1String("string"), 1); // control check
+        ptr = QSharedPointer<NoDefaultConstructorConstRef2>::create(QLatin1String("string"), 1);
+        QCOMPARE(ptr->str, QString("string"));
+        QCOMPARE(ptr->i, 1);
+
+        NoDefaultConstructorConstRef2(QByteArray("bytearray")); // control check
+        ptr = QSharedPointer<NoDefaultConstructorConstRef2>::create(QByteArray("bytearray"));
+        QCOMPARE(ptr->str, QString("bytearray"));
+        QCOMPARE(ptr->i, 42);
+    }
+#endif
+}
+
 void tst_QSharedPointer::creatingQObject()
 {
     {