tmp: Updated to store and preserve the const-ness of the reference to a constant object

This change requires that the de-reference operator '()' returns a
const-reference to the object stored irrespective of the const-ness of
object stored and the new member function 'ref()' is provided to return
an non-const reference to stored object which throws a fatal error if the
stored object is const.

In order to smooth the transition to this new safer 'tmp' the now
deprecated and unsafe non-const de-reference operator '()' is still
provided by default but may be switched-off with the compilation switch
'CONST_TMP'.

The main OpenFOAM library has already been upgraded and '-DCONST_TMP'
option specified in the 'options' file to switch to the new 'tmp'
behavior.  The rest of OpenFOAM-dev will be upgraded over the following
few weeks.

Henry G. Weller
CFD Direct

src/OpenFOAM/memory/tmp/tmp.H

@@ -52,15 +52,20 @@ class tmp
 {
     // Private data
 
-        //- Flag for whether object is a temporary or a constant object
-        bool isTmp_;
+        //- Object types
+        enum type
+        {
+            TMP,
+            REF,
+            CONST_REF
+        };
 
-        //- Pointer to temporary object
+        //- Type of object
+        type type_;
+
+        //- Pointer to object
         mutable T* ptr_;
 
-        //- Const reference to constant object
-        const T& ref_;
-
 
 public:
 
@@ -69,9 +74,15 @@ public:
         //- Store object pointer
         inline explicit tmp(T* = 0);
 
+        //- Store object rvalue reference
+        inline tmp(T&&);
+
         //- Store object const reference
         inline tmp(const T&);
 
+        //- Construct copy and increment reference count
+        inline tmp(tmp<T>&&);
+
         //- Construct copy and increment reference count
         inline tmp(const tmp<T>&);
 
@@ -100,6 +111,10 @@ public:
 
         // Edit
 
+            //- Return non-const reference or generate a fatal error
+            //  if the object is const.
+            inline T& ref();
+
             //- Return tmp pointer for reuse.
             //  Returns a clone if the object is not a temporary
             inline T* ptr() const;
@@ -111,8 +126,11 @@ public:
 
     // Member operators
 
-        //- Dereference operator
+        #ifndef CONST_TMP
+        //- Deprecated non-const dereference operator.
+        //  Use ref() where non-const access is required
         inline T& operator()();
+        #endif
 
         //- Const dereference operator
         inline const T& operator()() const;