ENH: add tmp/refPtr support for setting cref/ref from pointer

- makes it easier to use for local or alternative storage.
  Eg,

  ```
      tmp<volScalarField> tfld;

      tfld.cref(obj.cfindObject<volScalarField>("name"));

      if (!tfld)
      {
          tfld = volScalarField::New("name", ...);
      }
  ```

applications/test/refPtr/Test-refPtr.C

@@ -85,6 +85,12 @@ int main()
         ptr.reset(new scalarField(5, scalar(15)));
         tfld3.reset(std::move(ptr));
         printInfo(tfld3, true);
+
+
+        ptr.reset(new scalarField(2, scalar(1)));
+        Info<< nl << "const-ref from pointer: " << name(ptr.get()) << nl;
+        tfld3.cref(ptr.get());
+        printInfo(tfld3, true);
     }
 
     Info<< "\nEnd" << endl;

applications/test/tmp/Test-tmp.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2018-2020 OpenCFD Ltd.
+    Copyright (C) 2018-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -110,6 +110,12 @@ int main()
             Info<< "Reset to some other tmp content : ";
             printInfo(tfld2);
         }
+
+        std::unique_ptr<scalarField> ptr(new scalarField(2, scalar(1)));
+
+        Info<< nl << "const-ref from pointer: " << name(ptr.get()) << nl;
+        tfld2.cref(ptr.get());
+        printInfo(tfld2);
     }
 
     Info<< "\nEnd" << endl;

src/OpenFOAM/memory/refPtr/refPtr.H

@@ -215,12 +215,20 @@ public:
         //- Clear existing and transfer ownership.
         inline void reset(refPtr<T>&& other) noexcept;
 
-        //- Delete managed temporary object and set to (const) reference
+        //- Clear existing and set (const) reference
         inline void cref(const T& obj) noexcept;
 
-        //- Delete managed temporary object and set to (non-const) reference
+        //- Clear existing and set (const) reference to pointer content.
+        //  A null pointer is permitted (treated as a managed pointer).
+        inline void cref(const T* p) noexcept;
+
+        //- Clear existing and set (non-const) reference
         inline void ref(T& obj) noexcept;
 
+        //- Clear existing and set (non-const) reference to pointer content.
+        //  A null pointer is permitted (treated as a managed pointer).
+        inline void ref(T* p) noexcept;
+
         //- Swaps the managed object with other.
         inline void swap(refPtr<T>& other) noexcept;
 

src/OpenFOAM/memory/refPtr/refPtrI.H

@@ -300,6 +300,15 @@ inline void Foam::refPtr<T>::cref(const T& obj) noexcept
 }
 
 
+template<class T>
+inline void Foam::refPtr<T>::cref(const T* p) noexcept
+{
+    clear();
+    ptr_ = const_cast<T*>(p);
+    type_ = (ptr_ ? CREF : PTR);
+}
+
+
 template<class T>
 inline void Foam::refPtr<T>::ref(T& obj) noexcept
 {
@@ -309,6 +318,15 @@ inline void Foam::refPtr<T>::ref(T& obj) noexcept
 }
 
 
+template<class T>
+inline void Foam::refPtr<T>::ref(T* p) noexcept
+{
+    clear();
+    ptr_ = p;
+    type_ = (ptr_ ? REF : PTR);
+}
+
+
 template<class T>
 inline void Foam::refPtr<T>::swap(refPtr<T>& other) noexcept
 {

src/OpenFOAM/memory/tmp/tmp.H

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2018-2020 OpenCFD Ltd.
+    Copyright (C) 2018-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -224,12 +224,20 @@ public:
         //- Clear existing and transfer ownership.
         inline void reset(tmp<T>&& other) noexcept;
 
-        //- Delete managed temporary object and set to (const) reference
+        //- Clear existing and set (const) reference
         inline void cref(const T& obj) noexcept;
 
-        //- Delete managed temporary object and set to (non-const) reference
+        //- Clear existing and set (const) reference to pointer content.
+        //  A null pointer is permitted (treated as a managed pointer).
+        inline void cref(const T* p) noexcept;
+
+        //- Clear existing and set to (non-const) reference
         inline void ref(T& obj) noexcept;
 
+        //- Clear existing and set (non-const) reference to pointer content.
+        //  A null pointer is permitted (treated as a managed pointer).
+        inline void ref(T* p) noexcept;
+
         //- Swaps the managed object with other.
         inline void swap(tmp<T>& other) noexcept;
 

src/OpenFOAM/memory/tmp/tmpI.H

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2018-2020 OpenCFD Ltd.
+    Copyright (C) 2018-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -340,6 +340,15 @@ inline void Foam::tmp<T>::cref(const T& obj) noexcept
 }
 
 
+template<class T>
+inline void Foam::tmp<T>::cref(const T* p) noexcept
+{
+    clear();
+    ptr_ = const_cast<T*>(p);
+    type_ = (ptr_ ? CREF : PTR);
+}
+
+
 template<class T>
 inline void Foam::tmp<T>::ref(T& obj) noexcept
 {
@@ -349,6 +358,15 @@ inline void Foam::tmp<T>::ref(T& obj) noexcept
 }
 
 
+template<class T>
+inline void Foam::tmp<T>::ref(T* p) noexcept
+{
+    clear();
+    ptr_ = p;
+    type_ = (ptr_ ? REF : PTR);
+}
+
+
 template<class T>
 inline void Foam::tmp<T>::swap(tmp<T>& other) noexcept
 {