ENH: add Xfer rvalue(), valid() methods

- rvalue() is a (transitional) means of converting Xfer content to a
  reference for move construct, move assign semantics.

- valid() method for consistency with autoPtr and tmp classes

src/OpenFOAM/memory/Xfer/Xfer.H

@@ -79,7 +79,11 @@ class Xfer
 
 public:
 
-    typedef T Type;
+    // STL type definition similar to std::shared_ptr
+
+        //- Type of object being managed
+        typedef T element_type;
+
 
     // Constructors
 
@@ -107,11 +111,17 @@ public:
 
     // Member Functions
 
-        //- Pointer to the underlying object
+        //- Test for valid pointer and not a nullObject reference.
+        inline bool valid() const;
+
+        //- Pointer to the underlying object.
         inline T* get() const;
 
+        //- Rvalue reference to the underlying object.
+        inline T&& rvalue() const;
+
         //- Swaps the managed objects
-        void swap(Xfer<T>& other) noexcept;
+        inline void swap(Xfer<T>& other) noexcept;
 
 
     // Member Operators

src/OpenFOAM/memory/Xfer/XferI.H

@@ -39,8 +39,7 @@ template<class T>
 template<class... Args>
 inline Foam::Xfer<T> Foam::Xfer<T>::New(Args&&... args)
 {
-    T* ptr = new T(std::forward<Args>(args)...);
-    return Foam::Xfer<T>(ptr);
+    return Xfer<T>(new T(std::forward<Args>(args)...));
 }
 
 
@@ -69,6 +68,13 @@ inline Foam::Xfer<T>::Xfer(const Xfer<T>& xf)
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
+template<class T>
+inline bool Foam::Xfer<T>::valid() const
+{
+    return (ptr_ && Foam::notNull(ptr_));
+}
+
+
 template<class T>
 inline T* Foam::Xfer<T>::get() const
 {
@@ -76,13 +82,21 @@ inline T* Foam::Xfer<T>::get() const
 }
 
 
+template<class T>
+inline T&& Foam::Xfer<T>::rvalue() const
+{
+    // Need check for valid() ?
+    return std::move(*ptr_);
+}
+
+
 template<class T>
 inline void Foam::Xfer<T>::swap(Xfer<T>& other) noexcept
 {
     // Swap pointers
-    T* tmp = ptr_;
+    T* p = ptr_;
     ptr_ = other.ptr;
-    other.ptr_ = tmp;
+    other.ptr_ = p;
 }