QSharedPointer: allow one create() argument in C++98, too

Survey says that most uses of QSharedPointer(T*) in Qt that could benefit from
variadic create() pass only a single argument. In order to prevent all such
uses from #ifdef'ing on the complex condition that enables the variadic version,
provide a single-argument version (for lvalues only, obviously) for C++98, too.

Change-Id: I22ad251a20bbf80867cc31eaa3bcec677bde4359
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qsharedpointer.cpp

@@ -630,9 +630,15 @@
     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
+    \note This function is only fully 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,
+    then a restricted version is available since Qt 5.4: you may pass
+    one (but just one) argument, and it will always be passed by const
+    reference.
+
+    If you target Qt before version 5.4, you must use the overload
     that calls the default constructor.
 */
 

src/corelib/tools/qsharedpointer_impl.h

@@ -437,6 +437,27 @@ public:
         new (result.data()) T();
 # ifdef QT_SHAREDPOINTER_TRACK_POINTERS
         internalSafetyCheckAdd(result.d, result.value);
+# endif
+        result.d->setQObjectShared(result.value, true);
+        return result;
+    }
+
+    template <typename Arg>
+    static inline QSharedPointer create(const Arg &arg)
+    {
+        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 result(Qt::Uninitialized);
+        result.d = Private::create(&result.value, destroy);
+
+        // now initialize the data
+        new (result.data()) T(arg);
+# ifdef QT_SHAREDPOINTER_TRACK_POINTERS
+        internalSafetyCheckAdd(result.d, result.value);
 # endif
         result.d->setQObjectShared(result.value, true);
         return result;