ENH: support tuple (pair) indexing into FieldField

- can use a (patchi, elemi) pair to access an element of a FieldField

src/OpenFOAM/fields/FieldFields/FieldField/FieldField.C

@@ -297,6 +297,20 @@ tmp<FieldField<Field, Type>> FieldField<Field, Type>::T() const
 
 // * * * * * * * * * * * * * * * Member Operators  * * * * * * * * * * * * * //
 
+template<template<class> class Field, class Type>
+const Type& FieldField<Field, Type>::operator[](const labelPair& index) const
+{
+    return this->operator[](index.first())[index.second()];
+}
+
+
+template<template<class> class Field, class Type>
+Type& FieldField<Field, Type>::operator[](const labelPair& index)
+{
+    return this->operator[](index.first())[index.second()];
+}
+
+
 template<template<class> class Field, class Type>
 void FieldField<Field, Type>::operator=(const FieldField<Field, Type>& ff)
 {
@@ -356,6 +370,16 @@ void FieldField<Field, Type>::operator=(const Type& val)
 }
 
 
+template<template<class> class Field, class Type>
+void FieldField<Field, Type>::operator=(const Foam::zero)
+{
+    forAll(*this, i)
+    {
+        this->operator[](i) = Foam::zero{};
+    }
+}
+
+
 #define COMPUTED_ASSIGNMENT(TYPE, op)                                          \
                                                                                \
 template<template<class> class Field, class Type>                              \

src/OpenFOAM/fields/FieldFields/FieldField/FieldField.H

@@ -39,6 +39,7 @@ SourceFiles
 #define Foam_FieldField_H
 
 #include "tmp.H"
+#include "Pair.H"
 #include "PtrList.H"
 #include "scalar.H"
 #include "direction.H"
@@ -79,7 +80,6 @@ class FieldField
     public refCount,
     public PtrList<Field<Type>>
 {
-
 public:
 
     //- Component type
@@ -153,7 +153,16 @@ public:
         tmp<FieldField<Field, Type>> T() const;
 
 
-    // Member operators
+    // Member Operators
+
+        //- Const or non-const access to a field
+        using PtrList<Field<Type>>::operator[];
+
+        //- Const access to a single field element via (fieldi, elemi)
+        inline const Type& operator[](const labelPair& index) const;
+
+        //- Non-const access to a single field element via (fieldi, elemi)
+        inline Type& operator[](const labelPair& index);
 
         //- Copy assignment
         void operator=(const FieldField<Field, Type>&);
@@ -167,6 +176,9 @@ public:
         //- Assign uniform value
         void operator=(const Type& val);
 
+        //- Assign uniform zero
+        void operator=(const Foam::zero);
+
         void operator+=(const FieldField<Field, Type>&);
         void operator+=(const tmp<FieldField<Field, Type>>&);
 

src/OpenFOAM/fields/FieldFields/oneFieldField/oneFieldField.H

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2019-2020 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -37,10 +37,11 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef oneFieldField_H
-#define oneFieldField_H
+#ifndef Foam_oneFieldField_H
+#define Foam_oneFieldField_H
 
 #include "oneField.H"
+#include "Pair.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -65,10 +66,17 @@ public:
 
     // Member Operators
 
+        //- Return the field
         oneField operator[](const label) const noexcept
         {
             return oneField{};
         }
+
+        //- Return the field element
+        one operator[](const labelPair&) const noexcept
+        {
+            return one{};
+        }
 };
 
 

src/OpenFOAM/fields/FieldFields/zeroFieldField/zeroFieldField.H

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2019-2020 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -37,10 +37,11 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef zeroFieldField_H
-#define zeroFieldField_H
+#ifndef Foam_zeroFieldField_H
+#define Foam_zeroFieldField_H
 
 #include "zeroField.H"
+#include "Pair.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -65,10 +66,17 @@ public:
 
     // Member Operators
 
+        //- Return the field
         zeroField operator[](const label) const noexcept
         {
             return zeroField{};
         }
+
+        //- Return the field element
+        zero operator[](const labelPair&) const noexcept
+        {
+            return zero{};
+        }
 };
 
 

src/OpenFOAM/fields/Fields/oneField/oneField.H

@@ -36,11 +36,11 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef oneField_H
-#define oneField_H
+#ifndef Foam_oneField_H
+#define Foam_oneField_H
 
 #include "one.H"
-#include "scalar.H"
+#include "scalarFwd.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 

src/OpenFOAM/fields/Fields/zeroField/zeroField.H

@@ -36,11 +36,11 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef zeroField_H
-#define zeroField_H
+#ifndef Foam_zeroField_H
+#define Foam_zeroField_H
 
 #include "zero.H"
-#include "scalar.H"
+#include "scalarFwd.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //