ENH: zero::null::dummy, when dereferencing and dummy assignment are needed

src/OpenFOAM/global/global.Cver

@@ -88,9 +88,10 @@ const std::string Foam::foamVersion::version
 #include "new.C"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-// Create the nullObject singleton
+// The nullObject singleton and a dummy zero singleton
 
 #include "nullObject.C"
+#include "zero.C"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 // Global IO streams

src/OpenFOAM/primitives/zero/zero.C

@@ -0,0 +1,33 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2019 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "zero.H"
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+Foam::zero::null Foam::zero::null::dummy;
+
+
+// ************************************************************************* //

src/OpenFOAM/primitives/zero/zero.H

@@ -29,6 +29,7 @@ Description
     manipulating objects that are known to be 'zero' at compile-time.
 
 SourceFiles
+    zero.C
     zeroI.H
 
 \*---------------------------------------------------------------------------*/
@@ -105,6 +106,9 @@ class zero::null
 public:
     typedef null value_type;
 
+    //- A static zero::null for dereferencing as a dummy element
+    static null dummy;
+
     //- Null constructible
     constexpr null() noexcept{}