functionObjects: New abstract base-class 'fieldExpression' for simple field expression evaluation functionObjects

Updated and simplified 'div', 'grad' and 'mag' functionObjects by deriving from 'fieldExpression'.
Corrected the handling of cached gradients in 'grad'.

src/postProcessing/functionObjects/field/fieldExpression/fieldExpression.C

@@ -0,0 +1,81 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2016 OpenFOAM Foundation
+     \\/     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 "fieldExpression.H"
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace functionObjects
+{
+    defineTypeNameAndDebug(fieldExpression, 0);
+}
+}
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+Foam::functionObjects::fieldExpression::fieldExpression
+(
+    const word& name,
+    const Time& runTime,
+    const dictionary& dict
+)
+:
+    fvMeshFunctionObject(name, runTime, dict)
+{
+    read(dict);
+}
+
+
+// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
+
+Foam::functionObjects::fieldExpression::~fieldExpression()
+{}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+bool Foam::functionObjects::fieldExpression::read(const dictionary& dict)
+{
+    dict.lookup("field") >> fieldName_;
+
+    if (dict.found("result"))
+    {
+        dict.lookup("result") >> resultName_;
+    }
+
+    return true;
+}
+
+
+bool Foam::functionObjects::fieldExpression::write(const bool postProcess)
+{
+    return fvMeshFunctionObject::write(resultName_);
+}
+
+
+// ************************************************************************* //