From 5635e14f8194ff3746aa3d75e9d5e2fc60dd3513 Mon Sep 17 00:00:00 2001
From: Mark Olesen <Mark.Olesen@esi-group.com>
Date: Fri, 30 Jun 2023 18:43:41 +0200
Subject: [PATCH] ENH: add low-level polymorphic/boxed exprValue

- primarily for handling expression results,
  but can also be used as a universal value holder.

  Has some characteristics suitable for type-less IO:
  eg, is_integral(), nComponents()

ENH: add is_pointer() check for expression scanToken
---
 .../test/exprTraits/Test-exprTraits.C         |  53 +--
 applications/test/exprValue/Make/files        |   3 +
 applications/test/exprValue/Make/options      |   2 +
 applications/test/exprValue/Test-exprValue.C  | 141 +++++++
 src/OpenFOAM/Make/files                       |   1 +
 .../expressions/exprString/exprString.H       |   2 +-
 .../expressions/scanToken/exprScanToken.C     |  18 +-
 .../expressions/scanToken/exprScanToken.H     |  16 +-
 src/OpenFOAM/expressions/traits/exprTraits.C  | 112 ++++--
 src/OpenFOAM/expressions/traits/exprTraits.H  |  83 ++++-
 src/OpenFOAM/expressions/value/exprValue.C    | 341 +++++++++++++++++
 src/OpenFOAM/expressions/value/exprValue.H    | 348 ++++++++++++++++++
 src/OpenFOAM/expressions/value/exprValueI.H   | 213 +++++++++++
 13 files changed, 1243 insertions(+), 90 deletions(-)
 create mode 100644 applications/test/exprValue/Make/files
 create mode 100644 applications/test/exprValue/Make/options
 create mode 100644 applications/test/exprValue/Test-exprValue.C
 create mode 100644 src/OpenFOAM/expressions/value/exprValue.C
 create mode 100644 src/OpenFOAM/expressions/value/exprValue.H
 create mode 100644 src/OpenFOAM/expressions/value/exprValueI.H

diff --git a/applications/test/exprTraits/Test-exprTraits.C b/applications/test/exprTraits/Test-exprTraits.C
index f6a835871d..ab4bc40d15 100644
--- a/applications/test/exprTraits/Test-exprTraits.C
+++ b/applications/test/exprTraits/Test-exprTraits.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -17,8 +17,9 @@ Description
 
 #include "IOstreams.H"
 #include "ITstream.H"
-#include "exprTraits.H"
 #include "uLabel.H"
+
+#include "exprTraits.H"
 #include "error.H"
 #include "stringList.H"
 #include "exprScanToken.H"
@@ -27,16 +28,18 @@ using namespace Foam;
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-template<class T>
+template<class Type>
 void printTraits()
 {
-    const auto typeCode = exprTypeTraits<T>::value;
+    const auto typeCode = exprTypeTraits<Type>::value;
 
-    Info<< "type " << pTraits<T>::typeName
-        << " code:" << int(typeCode)
-        << " name:" << exprTypeTraits<T>::name;
+    Info<< "Type '" << pTraits<Type>::typeName
+        << "' = code:" << int(typeCode)
+        << " rank:" << exprTypeTraits<Type>::rank
+        << " cmpt:" << exprTypeTraits<Type>::nComponents
+        << " name:" << exprTypeTraits<Type>::name;
 
-    if (pTraits<T>::typeName != word(exprTypeTraits<T>::name))
+    if (pTraits<Type>::typeName != word(exprTypeTraits<Type>::name))
     {
         Info<< " (UNSUPPORTED)";
     }
@@ -45,6 +48,17 @@ void printTraits()
 }
 
 
+void print(const expressions::scanToken& tok)
+{
+    Info<< "    type:" << int(tok.type_);
+    if (tok.is_pointer())
+    {
+        Info<< " ptr:" << Foam::name(tok.name_);
+    }
+    Info<< nl;
+}
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 int main()
@@ -56,6 +70,7 @@ int main()
     printTraits<bool>();
     printTraits<label>();
     printTraits<scalar>();
+    printTraits<complex>();
     printTraits<vector>();
     printTraits<tensor>();
     printTraits<symmTensor>();
@@ -71,33 +86,27 @@ int main()
     Info<< "Name of typeCode: "
         << getName(expressions::valueTypeCode::type_bool) << nl;
 
-
     {
-        expressions::scanToken tok;
-        expressions::scanToken tok2;
+        expressions::scanToken tok(expressions::scanToken::null());
+        expressions::scanToken tok2(expressions::scanToken::null());
 
         Info<< nl << "sizeof(scanToken): "
             << sizeof(tok) << nl;
 
-        Info<< "    type:" << int(tok.type_) << nl;
-        Info<< "    ptr:" << Foam::name(tok.name_) << nl;
-
-        Info<< "    type:" << int(tok2.type_) << nl;
-        Info<< "    ptr:" << Foam::name(tok2.name_) << nl;
+        print(tok);
+        print(tok2);
 
         tok.setWord("hello");
 
-        Info<< "    type:" << int(tok.type_) << nl;
-        Info<< "    ptr:" << Foam::name(tok.name_) << nl;
+        print(tok);
 
         tok2 = tok;
-        Info<< "    type:" << int(tok2.type_) << nl;
-        Info<< "    ptr:" << Foam::name(tok2.name_) << nl;
+        print(tok2);
 
         tok2.destroy();
 
-        Info<< "    type:" << int(tok2.type_) << nl;
-        Info<< "    ptr:" << Foam::name(tok2.name_) << nl;
+        print(tok);  // Not a leak, but old rubbish
+        print(tok2);
     }
 
     Info<< nl << "Done" << nl;
diff --git a/applications/test/exprValue/Make/files b/applications/test/exprValue/Make/files
new file mode 100644
index 0000000000..312329154a
--- /dev/null
+++ b/applications/test/exprValue/Make/files
@@ -0,0 +1,3 @@
+Test-exprValue.C
+
+EXE = $(FOAM_USER_APPBIN)/Test-exprValue
diff --git a/applications/test/exprValue/Make/options b/applications/test/exprValue/Make/options
new file mode 100644
index 0000000000..18e6fe47af
--- /dev/null
+++ b/applications/test/exprValue/Make/options
@@ -0,0 +1,2 @@
+/* EXE_INC = */
+/* EXE_LIBS = */
diff --git a/applications/test/exprValue/Test-exprValue.C b/applications/test/exprValue/Test-exprValue.C
new file mode 100644
index 0000000000..fc48f6b534
--- /dev/null
+++ b/applications/test/exprValue/Test-exprValue.C
@@ -0,0 +1,141 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021-2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
+
+Application
+    Test-exprValue
+
+Description
+    Test low-level polymorphic value container (exprValue)
+
+\*---------------------------------------------------------------------------*/
+
+#include "argList.H"
+#include "IOstreams.H"
+#include "ITstream.H"
+#include "exprValue.H"
+
+using namespace Foam;
+
+void printInfo(const expressions::exprValue& val)
+{
+    Info<< "Boxed type:" << int(val.typeCode())
+        << " (" << val.valueTypeName() << ") good:"
+        << val.good() << " => " << val << nl;
+}
+
+
+expressions::exprValue tryParse(const std::string& str)
+{
+    expressions::exprValue val, val2;
+
+    ITstream is(str);
+
+    const bool ok = val.read(is);
+
+    Info<< "read " << Foam::name(val.typeCode()) << " from " << str;
+
+    if (ok)
+    {
+        Info<< " trailing tokens:" << is.nRemainingTokens() << nl
+            << "value: " << val << nl;
+    }
+    else
+    {
+        Info<< " FAILED" << nl;
+    }
+
+    if (ok)
+    {
+        Info<< "Direct from string: ";
+        if (expressions::exprValue::read(str, val2))
+        {
+            Info<< "good" << nl;
+        }
+        else
+        {
+            Info<< "bad" << nl;
+        }
+    }
+    return val;
+}
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+int main(int argc, char *argv[])
+{
+    argList::noBanner();
+    argList::noParallel();
+
+    #include "setRootCase.H"
+
+    // Aborts
+    // expressions::exprValue value(std::string(""));
+
+    {
+        expressions::exprValue value;
+
+        // Nothing
+        printInfo(value);
+
+        value.set(scalar(100));
+        printInfo(value);
+
+        value.set(vector(1,2,3));
+        printInfo(value);
+
+        value = vector(4,5,6);
+        printInfo(value);
+
+        value = Zero;
+        printInfo(value);
+
+        value.clear();
+        printInfo(value);
+
+        value = 100 * vector(1,0,0);
+        printInfo(value);
+    }
+
+
+    {
+        Info<< nl << "Test parsing" << nl << nl;
+
+        for
+        (
+            const auto& input :
+            stringList
+            ({
+                "()",  // bad
+                "( 1 2  ",  // also bad
+                "(  ",  // really bad
+                "(1 16 12)",
+                "(1 bad)",
+                "(5)",
+                "1.2345",
+                "5.678 trailing",
+                "true",
+                "false",
+                " 1 ",
+                "  yes no "
+            })
+        )
+        {
+            (void) tryParse(input);
+        }
+    }
+
+    return 0;
+}
+
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/Make/files b/src/OpenFOAM/Make/files
index 0edb074fde..286516413f 100644
--- a/src/OpenFOAM/Make/files
+++ b/src/OpenFOAM/Make/files
@@ -183,6 +183,7 @@ $(expr)/exprTools/exprTools.C
 $(expr)/scanToken/exprScanToken.C
 
 $(expr)/traits/exprTraits.C
+$(expr)/value/exprValue.C
 
 $(expr)/exprDriver/exprDriver.C
 $(expr)/exprDriver/exprDriverFields.C
diff --git a/src/OpenFOAM/expressions/exprString/exprString.H b/src/OpenFOAM/expressions/exprString/exprString.H
index 34e114dbb2..87a07668d5 100644
--- a/src/OpenFOAM/expressions/exprString/exprString.H
+++ b/src/OpenFOAM/expressions/exprString/exprString.H
@@ -24,7 +24,7 @@ License
     You should have received a copy of the GNU General Public License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
-Namespace
+Class
     Foam::expressions::exprString
 
 Description
diff --git a/src/OpenFOAM/expressions/scanToken/exprScanToken.C b/src/OpenFOAM/expressions/scanToken/exprScanToken.C
index 63d6f87f8c..66b10d3c61 100644
--- a/src/OpenFOAM/expressions/scanToken/exprScanToken.C
+++ b/src/OpenFOAM/expressions/scanToken/exprScanToken.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -32,7 +32,7 @@ License
 Foam::expressions::scanToken Foam::expressions::scanToken::null()
 {
     scanToken tok;
-    tok.type_ = LABEL;
+    tok.type_ = tokenType::LABEL;
     tok.labelValue = 0;
 
     return tok;
@@ -41,12 +41,12 @@ Foam::expressions::scanToken Foam::expressions::scanToken::null()
 
 void Foam::expressions::scanToken::destroy()
 {
-    if (type_ == VECTOR)
+    if (type_ == tokenType::VECTOR)
     {
         delete vectorPtr;
         vectorPtr = nullptr;
     }
-    else if (type_ == WORD)
+    else if (type_ == tokenType::WORD)
     {
         delete wordPtr;
         wordPtr = nullptr;
@@ -56,35 +56,35 @@ void Foam::expressions::scanToken::destroy()
 
 void Foam::expressions::scanToken::setLabel(label val)
 {
-    type_ = LABEL;
+    type_ = tokenType::LABEL;
     labelValue = val;
 }
 
 
 void Foam::expressions::scanToken::setScalar(scalar val)
 {
-    type_ = SCALAR;
+    type_ = tokenType::SCALAR;
     scalarValue = val;
 }
 
 
 void Foam::expressions::scanToken::setVector(scalar x, scalar y, scalar z)
 {
-    type_ = VECTOR;
+    type_ = tokenType::VECTOR;
     vectorPtr = new Foam::vector(x, y, z);
 }
 
 
 void Foam::expressions::scanToken::setVector(const vector& val)
 {
-    type_ = VECTOR;
+    type_ = tokenType::VECTOR;
     vectorPtr = new Foam::vector(val);
 }
 
 
 void Foam::expressions::scanToken::setWord(const word& val)
 {
-    type_ = WORD;
+    type_ = tokenType::WORD;
     wordPtr = new Foam::word(val);
 }
 
diff --git a/src/OpenFOAM/expressions/scanToken/exprScanToken.H b/src/OpenFOAM/expressions/scanToken/exprScanToken.H
index 5bdf2f6357..185d154afc 100644
--- a/src/OpenFOAM/expressions/scanToken/exprScanToken.H
+++ b/src/OpenFOAM/expressions/scanToken/exprScanToken.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019-2021 OpenCFD Ltd.
+    Copyright (C) 2019-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -33,13 +33,15 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef expressions_scanToken_H
-#define expressions_scanToken_H
+#ifndef Foam_expressions_scanToken_H
+#define Foam_expressions_scanToken_H
 
 #include "scalar.H"
 #include "vector.H"
 #include "word.H"
 
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
 namespace Foam
 {
 namespace expressions
@@ -80,7 +82,7 @@ struct scanToken
 
     // Member Functions
 
-        //- Return a null token - in lieu of a default constructor
+        //- Return a null token (label = 0) - in lieu of a default constructor
         static scanToken null();
 
         //- Assign type/value to be LABEL. Does not call destroy().
@@ -98,6 +100,12 @@ struct scanToken
         //- Assign type/value to be WORD (name). Does not call destroy().
         void setWord(const word& val);
 
+        //- True if a pointer type
+        bool is_pointer() const noexcept
+        {
+            return (type_ == tokenType::VECTOR || type_ == tokenType::WORD);
+        }
+
         //- Manual deletion of pointer types
         void destroy();
 };
diff --git a/src/OpenFOAM/expressions/traits/exprTraits.C b/src/OpenFOAM/expressions/traits/exprTraits.C
index 2f4dda37a4..3e6a389536 100644
--- a/src/OpenFOAM/expressions/traits/exprTraits.C
+++ b/src/OpenFOAM/expressions/traits/exprTraits.C
@@ -27,45 +27,82 @@ License
 
 #include "exprTraits.H"
 
+//TBD: handle complex?
+
+#undef  FOR_ALL_EXPR_TYPE_CODES
+#define FOR_ALL_EXPR_TYPE_CODES(Macro, ...)                                   \
+    Macro(bool, __VA_ARGS__)                                                  \
+    Macro(label, __VA_ARGS__)                                                 \
+    Macro(scalar, __VA_ARGS__)                                                \
+    Macro(vector, __VA_ARGS__)                                                \
+    Macro(sphericalTensor, __VA_ARGS__)                                       \
+    Macro(symmTensor, __VA_ARGS__)                                            \
+    Macro(tensor, __VA_ARGS__)
+
+
 // * * * * * * * * * * * * * * * Global Functions  * * * * * * * * * * * * * //
 
-Foam::expressions::valueTypeCode
-Foam::expressions::valueTypeCodeOf(const word& dataTypeName)
+Foam::direction
+Foam::expressions::Detail::nComponents
+(
+    const expressions::valueTypeCode typeCode
+) noexcept
 {
-    #undef  stringToTypeCode
-    #define stringToTypeCode(Type)                                  \
-                                                                    \
-    if (dataTypeName == exprTypeTraits<Type>::name)                 \
-    {                                                               \
-        return expressions::valueTypeCode::type_##Type;             \
+    switch (typeCode)
+    {
+        case expressions::valueTypeCode::NONE :
+        case expressions::valueTypeCode::INVALID :
+        {
+            break;
+        }
+
+        #undef  doLocalCode
+        #define doLocalCode(Type, UnusedParam)                        \
+                                                                      \
+        case expressions::valueTypeCode::type_##Type :                \
+        {                                                             \
+            return pTraits<Type>::nComponents;                        \
+        }
+
+        FOR_ALL_EXPR_TYPE_CODES(doLocalCode);
+        #undef doLocalCode
     }
 
+    return 0;
+}
+
+
+Foam::expressions::valueTypeCode
+Foam::expressions::valueTypeCodeOf
+(
+    const word& dataTypeName,
+    const expressions::valueTypeCode deflt
+)
+{
     if (!dataTypeName.empty())
     {
-        stringToTypeCode(bool);
-        stringToTypeCode(label);
-        stringToTypeCode(scalar);
-        stringToTypeCode(vector);
-        stringToTypeCode(tensor);
-        stringToTypeCode(sphericalTensor);
-        stringToTypeCode(symmTensor);
-    }
-    #undef stringToTypeCode
+        // Could compare with pTraits<Type>::typeName instead of
+        // exprTypeTraits<Type>::name, but then we might miss
+        // possible typos.
 
-    return expressions::valueTypeCode::INVALID;
+        #undef  doLocalCode
+        #define doLocalCode(Type, UnusedParam)                        \
+                                                                      \
+        if (dataTypeName == exprTypeTraits<Type>::name)               \
+        {                                                             \
+            return expressions::valueTypeCode::type_##Type;           \
+        }
+
+        FOR_ALL_EXPR_TYPE_CODES(doLocalCode);
+        #undef doLocalCode
+    }
+
+    return deflt;
 }
 
 
 Foam::word Foam::name(const expressions::valueTypeCode typeCode)
 {
-    #undef  case_typeCodeToString
-    #define case_typeCodeToString(Type)                             \
-                                                                    \
-    case expressions::valueTypeCode::type_##Type :                  \
-    {                                                               \
-        return exprTypeTraits<Type>::name;                          \
-    }
-
     switch (typeCode)
     {
         case expressions::valueTypeCode::NONE :
@@ -75,22 +112,27 @@ Foam::word Foam::name(const expressions::valueTypeCode typeCode)
 
         case expressions::valueTypeCode::INVALID :
         {
-            // ie, ""
+            // returns ""
             break;
         }
 
-        case_typeCodeToString(bool);
-        case_typeCodeToString(label);
-        case_typeCodeToString(scalar);
-        case_typeCodeToString(vector);
-        case_typeCodeToString(tensor);
-        case_typeCodeToString(sphericalTensor);
-        case_typeCodeToString(symmTensor);
+        #undef  doLocalCode
+        #define doLocalCode(Type, UnusedParam)                        \
+        case expressions::valueTypeCode::type_##Type :                \
+        {                                                             \
+            return exprTypeTraits<Type>::name;                        \
+        }
+
+        FOR_ALL_EXPR_TYPE_CODES(doLocalCode);
+        #undef doLocalCode
     }
-    #undef case_typeCodeToString
 
     return word();
 }
 
 
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#undef  FOR_ALL_EXPR_TYPE_CODES
+
 // ************************************************************************* //
diff --git a/src/OpenFOAM/expressions/traits/exprTraits.H b/src/OpenFOAM/expressions/traits/exprTraits.H
index 6c2173eea8..c3452da052 100644
--- a/src/OpenFOAM/expressions/traits/exprTraits.H
+++ b/src/OpenFOAM/expressions/traits/exprTraits.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -28,18 +28,33 @@ Class
 
 Description
     Simple type identifiers for polymorphic expression values.
-
     The definitions are similar to std::integral_constant in that they
     provide value, value_type (and name).
 
+SourceFiles
+    exprTraits.C
+
+Namespace
+    Foam::expressions
+
+Description
+    A namespace for expression-related classes/traits etc.
+
+Namespace
+    Foam::expressions::Detail
+
+Description
+    A namespace for implementation details related to expressions.
+
 \*---------------------------------------------------------------------------*/
 
-#ifndef expressions_exprTraits_H
-#define expressions_exprTraits_H
+#ifndef Foam_expressions_exprTraits_H
+#define Foam_expressions_exprTraits_H
 
 // Regular field types
 #include "label.H"
 #include "scalar.H"
+//TBD: #include "complex.H"
 #include "vector.H"
 #include "sphericalTensor.H"
 #include "symmTensor.H"
@@ -56,7 +71,7 @@ namespace expressions
 //- An enumeration of known and expected expression value types.
 //  Do not rely on the enumeration values for any direct coding.
 //
-//  \note NONE use used when initializing types, whereas INVALID is used
+//  \note NONE used when initializing types, whereas INVALID is used
 //  for unsupported types (never as a stored type).
 //  This avoids false positives when testing.
 //
@@ -72,6 +87,7 @@ enum class valueTypeCode : unsigned char
     type_bool,              //!< Type is 'bool'
     type_label,             //!< Type is 'label'
     type_scalar,            //!< Type is 'scalar'
+//TBD: type_complex,           //!< Type is 'complex'
 
     // Rank 1 types
     type_vector,            //!< Type is 'vector'
@@ -86,7 +102,23 @@ enum class valueTypeCode : unsigned char
 // Global Functions
 
 //- From string to valueTypeCode (if any)
-valueTypeCode valueTypeCodeOf(const word& dataTypeName);
+valueTypeCode valueTypeCodeOf
+(
+    const word& dataTypeName,
+    // Fallback for unknown
+    const expressions::valueTypeCode deflt = expressions::valueTypeCode::INVALID
+);
+
+
+// Some implementation detail
+namespace Detail
+{
+
+//- The number of components associated with given valueTypeCode
+::Foam::direction nComponents(const expressions::valueTypeCode) noexcept;
+
+} // End namespace Detail
+
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -101,45 +133,58 @@ valueTypeCode valueTypeCodeOf(const word& dataTypeName);
 template<class Type>
 struct exprTypeTraits
 {
+    // The value type
     typedef Type value_type;
+    // The type name (similar to pTraits typeName)
     static constexpr const char* const name = "";
+    // The enumeration number associated with the type
     static constexpr
         ::Foam::expressions::valueTypeCode value =
         ::Foam::expressions::valueTypeCode::INVALID;
+    // The rank of the type
+    static constexpr ::Foam::direction rank = 0;
+    // The number of components
+    static constexpr ::Foam::direction nComponents = 0;
 };
 
 
 #undef  defineExprTypeTraits
-#define defineExprTypeTraits(Type, Name)                                      \
+#define defineExprTypeTraits(Type, Name, Rank, NumCmpts)                      \
+    /*! \brief \c Name expression traits */                                   \
     template<>                                                                \
     struct exprTypeTraits<Type>                                               \
     {                                                                         \
         typedef Type value_type;                                              \
-        static constexpr const char* const name = #Name;                      \
+        static constexpr const char* const name = #Name ;                     \
         static constexpr                                                      \
             ::Foam::expressions::valueTypeCode value =                        \
-            ::Foam::expressions::valueTypeCode::type_##Name;                  \
+            ::Foam::expressions::valueTypeCode::type_##Name ;                 \
+        static constexpr ::Foam::direction rank = Rank ;                      \
+        static constexpr ::Foam::direction nComponents = NumCmpts ;           \
     };
 
 
-// Define with "name" to match regular pTraits typeName
-defineExprTypeTraits(bool, bool);
-defineExprTypeTraits(::Foam::label, label);
-defineExprTypeTraits(::Foam::scalar, scalar);
-defineExprTypeTraits(::Foam::vector, vector);
-defineExprTypeTraits(::Foam::tensor, tensor);
-defineExprTypeTraits(::Foam::sphericalTensor, sphericalTensor);
-defineExprTypeTraits(::Foam::symmTensor, symmTensor);
+// Define with name to match pTraits::typeName, with rank/nComponents
+defineExprTypeTraits(bool, bool, 0, 1);
+defineExprTypeTraits(::Foam::label, label, 0, 1);
+defineExprTypeTraits(::Foam::scalar, scalar, 0, 1);
+//TBD: defineExprTypeTraits(::Foam::complex, complex, 0, 2);
+defineExprTypeTraits(::Foam::vector, vector, 1, 3);
+defineExprTypeTraits(::Foam::tensor, tensor, 2, 9);
+defineExprTypeTraits(::Foam::sphericalTensor, sphericalTensor, 2, 1);
+defineExprTypeTraits(::Foam::symmTensor, symmTensor, 2, 6);
 
 #undef defineExprTypeTraits
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-//- A word representation of a valueTypeCode. Empty for INVALID
+//- A word representation of a valueTypeCode.
+//- Empty for expressions::valueTypeCode::INVALID
 word name(const expressions::valueTypeCode typeCode);
 
 
-//- A word representation of a valueTypeCode. Empty for INVALID
+//- A word representation of a valueTypeCode.
+//- Empty for expressions::valueTypeCode::INVALID
 template<>
 struct nameOp<expressions::valueTypeCode>
 {
diff --git a/src/OpenFOAM/expressions/value/exprValue.C b/src/OpenFOAM/expressions/value/exprValue.C
new file mode 100644
index 0000000000..e7ee984568
--- /dev/null
+++ b/src/OpenFOAM/expressions/value/exprValue.C
@@ -0,0 +1,341 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021-2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+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 "exprValue.H"
+#include "ITstream.H"
+#include "Switch.H"
+#include <cstring>  // For memcpy, memset
+
+// * * * * * * * * * * * * * * * Local Functions * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+template<class Type>
+static void fillTokens(const Type& val, tokenList& toks)
+{
+    const direction nCmpt = pTraits<Type>::nComponents;
+    const direction nParen = 2*(pTraits<Type>::rank || (nCmpt > 1) ? 1 : 0);
+
+    toks.resize_nocopy(nCmpt + nParen);
+
+    auto iter = toks.begin();
+
+    if (nParen)
+    {
+        *iter = token::BEGIN_LIST;
+        ++iter;
+    }
+
+    for (direction cmpt = 0; cmpt < nCmpt; ++cmpt)
+    {
+        *iter = component(val, cmpt);
+        ++iter;
+    }
+
+    if (nParen)
+    {
+        *iter = token::END_LIST;
+        ++iter;
+    }
+}
+
+
+//- Specialized for bool
+template<>
+void fillTokens<bool>(const bool& val, tokenList& toks)
+{
+    toks.resize_nocopy(1);
+    toks.front() = token::boolean(val);
+}
+
+
+//- Specialized for label
+template<>
+void fillTokens<label>(const label& val, tokenList& toks)
+{
+    toks.resize_nocopy(1);
+    toks.front() = val;
+}
+
+
+//- Specialized for scalar
+template<>
+void fillTokens<scalar>(const scalar& val, tokenList& toks)
+{
+    toks.resize_nocopy(1);
+    toks.front() = val;
+}
+
+} // End namespace Foam
+
+
+// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
+
+Foam::expressions::valueTypeCode
+Foam::expressions::exprValue::peekType(const ITstream& is)
+{
+    expressions::valueTypeCode whichCode(expressions::valueTypeCode::INVALID);
+
+    const token& tok0 = is.peek();
+
+    if (tok0.isPunctuation(token::BEGIN_LIST))
+    {
+        // Expecting "( content )" - eg, (x y z), (xx xy ...)
+
+        // First component starts after the opening '('.
+        // Can use the current index if the '(' actually came from
+        // the putBack.
+
+        const label firstCmpti = (is.tokenIndex() + (is.hasPutback() ? 0 : 1));
+
+        // Search for closing ')', require all components to be numbers
+        for (label endCmpti = firstCmpti; endCmpti < is.size(); ++endCmpti)
+        {
+            const token& tok = is[endCmpti];
+
+            ///InfoErr
+            ///    << "check token: " << (endCmpti-firstCmpti) << " : "
+            ///    << is[endCmpti].name() << nl;
+
+            if (tok.isPunctuation(token::END_LIST))
+            {
+                // Select based on the number of components
+                // cf. pTraits<Type>::nComponents
+
+                switch (endCmpti - firstCmpti)
+                {
+                    case 1:  // pTraits<sphericalTensor>::nComponents
+                        whichCode = exprTypeTraits<sphericalTensor>::value;
+                        break;
+
+                    // FUTURE?
+                    // case 2:  // pTraits<complex>::nComponents
+                    //     whichCode = exprTypeTraits<complex>::value;
+                    //     break;
+
+                    case 3:  // pTraits<vector>::nComponents
+                        whichCode = exprTypeTraits<vector>::value;
+                        break;
+
+                    case 6:  // pTraits<symmTensor>::nComponents
+                        whichCode = exprTypeTraits<symmTensor>::value;
+                        break;
+
+                    case 9:  // pTraits<tensor>::nComponents
+                        whichCode = exprTypeTraits<tensor>::value;
+                        break;
+                }
+
+                // Closing ')' terminates peeking
+                break;
+            }
+            else if (!tok.isNumber())
+            {
+                // All components should be numeric
+                break;
+            }
+        }
+    }
+    else if (tok0.good())
+    {
+        /// InfoErr<< "check token: " << tok0.info() << nl;
+
+        if (tok0.isScalar())
+        {
+            whichCode = exprTypeTraits<scalar>::value;
+        }
+        else if (tok0.isLabel())
+        {
+            whichCode = exprTypeTraits<label>::value;
+        }
+        else if (Switch(tok0).good())
+        {
+            whichCode = exprTypeTraits<bool>::value;
+        }
+    }
+
+    return whichCode;
+}
+
+
+bool Foam::expressions::exprValue::read
+(
+    const std::string& str,
+    exprValue& val
+)
+{
+    ITstream is(str);
+
+    // No trailing non-whitespace!
+    return (val.read(is) && !is.nRemainingTokens());
+}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+void Foam::expressions::exprValue::clear()
+{
+    std::memset(static_cast<void*>(this), '\0', sizeof(*this));
+    // Redundant:  typeCode_ = expressions::valueTypeCode::NONE;
+}
+
+
+void Foam::expressions::exprValue::deepCopy(const exprValue& rhs)
+{
+    if (this != &rhs)
+    {
+        // Self-assignment is a no-op
+        std::memcpy(static_cast<void*>(this), &rhs, sizeof(*this));
+    }
+}
+
+
+Foam::tokenList Foam::expressions::exprValue::tokens() const
+{
+    tokenList toks;
+
+    switch (typeCode_)
+    {
+        #undef  doLocalCode
+        #define doLocalCode(Type, UnusedParam)                        \
+                                                                      \
+        case expressions::valueTypeCode::type_##Type :                \
+        {                                                             \
+            const Type* dataPtr = data_.get<Type>();                  \
+            if (dataPtr)                                              \
+            {                                                         \
+                fillTokens<Type>(*dataPtr, toks);                     \
+            }                                                         \
+            break;                                                    \
+        }
+
+        FOR_ALL_EXPR_VALUE_TYPES(doLocalCode);
+        #undef doLocalCode
+
+        // exprValue may only be a subset of valueTypeCode types
+        default: break;
+    }
+
+    return toks;
+}
+
+
+void Foam::expressions::exprValue::print(Ostream& os) const
+{
+    switch (typeCode_)
+    {
+        #undef  doLocalCode
+        #define doLocalCode(Type, UnusedParam)                        \
+                                                                      \
+        case expressions::valueTypeCode::type_##Type :                \
+        {                                                             \
+            const Type* dataPtr = data_.get<Type>();                  \
+            if (dataPtr)                                              \
+            {                                                         \
+                os << *dataPtr;                                       \
+            }                                                         \
+            break;                                                    \
+        }
+
+        FOR_ALL_EXPR_VALUE_TYPES(doLocalCode);
+        #undef doLocalCode
+
+        // exprValue may only be a subset of valueTypeCode types
+        default: break;
+    }
+}
+
+
+bool Foam::expressions::exprValue::read(ITstream& is)
+{
+    clear();  // type: none, value: zero
+
+    const valueTypeCode whichCode(exprValue::peekType(is));
+
+    switch (whichCode)
+    {
+        #undef  doLocalCode
+        #define doLocalCode(Type, UnusedParam)                        \
+                                                                      \
+        case expressions::valueTypeCode::type_##Type :                \
+        {                                                             \
+            data_.set<Type>(pTraits<Type>(is));                       \
+            typeCode_ = whichCode;                                    \
+            return true;                                              \
+        }
+
+        FOR_ALL_EXPR_VALUE_TYPES(doLocalCode);
+        #undef doLocalCode
+
+        // exprValue may only be a subset of valueTypeCode types
+        default: break;
+    }
+
+    return false;
+}
+
+
+// * * * * * * * * * * * * * * * IOstream Operators  * * * * * * * * * * * * //
+
+Foam::Ostream& Foam::operator<<
+(
+    Ostream& os,
+    const expressions::exprValue& val
+)
+{
+    val.print(os);
+    return os;
+}
+
+
+template<>
+Foam::Ostream& Foam::operator<<
+(
+    Ostream& os,
+    const InfoProxy<expressions::exprValue>& iproxy
+)
+{
+    const auto& val = *iproxy;
+
+    if (val.good())
+    {
+        os  << val.valueTypeName() << ": ";
+        val.print(os);
+    }
+    else
+    {
+        // typeCode_ is *never* set to INVALID,
+        // so NONE is the only remaining non-good type
+        os  << "none";
+    }
+
+    return os;
+}
+
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/expressions/value/exprValue.H b/src/OpenFOAM/expressions/value/exprValue.H
new file mode 100644
index 0000000000..07260cc86b
--- /dev/null
+++ b/src/OpenFOAM/expressions/value/exprValue.H
@@ -0,0 +1,348 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021-2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+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/>.
+
+Class
+    Foam::expressions::exprValue
+
+Description
+    A polymorphic typed union of simple primitive and VectorSpace types.
+    It uses a 'fatter' representation that includes standard VectorSpace
+    types, which avoids heap allocations at the expense of more storage.
+    This is mostly not an issue since lists and fields would box/unbox
+    an entire field, not individual values.
+
+SourceFiles
+    exprValue.C
+    exprValueI.H
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef Foam_expressions_exprValue_H
+#define Foam_expressions_exprValue_H
+
+#include "exprTraits.H"
+#include "error.H"
+#include "tokenList.H"
+#include "InfoProxy.H"
+#include <typeinfo>
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Execute macro for known exprValue types, with more probably ones first
+#undef  FOR_ALL_EXPR_VALUE_TYPES
+#define FOR_ALL_EXPR_VALUE_TYPES(Macro, ...)                                  \
+    Macro(scalar, __VA_ARGS__)                                                \
+    Macro(vector, __VA_ARGS__)                                                \
+    Macro(tensor, __VA_ARGS__)                                                \
+    Macro(symmTensor, __VA_ARGS__)                                            \
+    Macro(sphericalTensor, __VA_ARGS__)                                       \
+    Macro(label, __VA_ARGS__)                                                 \
+    Macro(bool, __VA_ARGS__)
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+// Forward Declarations
+class ITstream;
+
+namespace expressions
+{
+namespace Detail
+{
+
+/*---------------------------------------------------------------------------*\
+                       Class exprValueUnion Declaration
+\*---------------------------------------------------------------------------*/
+
+//- The data content (as a union).
+//  The stem of the member names correspond identically to the data types
+//  to enable macro definitions (naming similar to Foam::token)
+union exprValueUnion
+{
+    // Member Data
+
+        #undef  declareUnionMember
+        #define declareUnionMember(Type, UnusedParam)                         \
+                                                                              \
+        /*! Define Type data member */                                        \
+        Type Type##Value;
+
+        FOR_ALL_EXPR_VALUE_TYPES(declareUnionMember);
+        #undef declareUnionMember
+
+
+    // Member Functions
+
+        //- Runtime 'assert' for unimplemented generic methods
+        //  This seems to be the best way to catch programming errors
+        //  since static_assert does not help here.
+        //  The 'noexcept' is slightly misleading (needed for the caller)
+        static void notSpecialized(const std::string& msg) noexcept
+        {
+            FatalErrorInFunction
+                << "non-specialized: " << msg.c_str() << endl
+                << abort(FatalError);
+        }
+
+        //- Return read pointer to typed union member,
+        //- which is nullptr for unspecialized versions
+        template<class Type>
+        inline const Type* get() const noexcept { return nullptr; }
+
+        //- No generic set(), only specialized methods
+        template<class Type>
+        inline void set(const Type& val) noexcept
+        {
+            notSpecialized("set<" + std::string(typeid(Type).name()) + '>');
+        }
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Type-specific get/set (definitions)
+#undef  defineMultiTypeValueUnionMethods
+#define defineMultiTypeValueUnionMethods(Type, UnusedParam)                   \
+                                                                              \
+/*! Return read pointer to Type union member */                               \
+template<>                                                                    \
+inline const Type* exprValueUnion::get<Type>() const noexcept                 \
+{                                                                             \
+    return &(Type##Value);                                                    \
+}                                                                             \
+                                                                              \
+/*! Set Type value */                                                         \
+template<>                                                                    \
+inline void exprValueUnion::set<Type>(const Type& val) noexcept               \
+{                                                                             \
+    Type##Value = val;                                                        \
+}
+
+// Type-specific methods
+FOR_ALL_EXPR_VALUE_TYPES(defineMultiTypeValueUnionMethods);
+#undef defineMultiTypeValueUnionMethods
+
+} // End namespace Detail
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+
+/*---------------------------------------------------------------------------*\
+                       Class exprValue Declaration
+\*---------------------------------------------------------------------------*/
+
+class exprValue
+{
+    // Private Data
+
+        //- The data content (as a union)
+        Detail::exprValueUnion data_;
+
+        //- The data type (as a type-code)
+        expressions::valueTypeCode typeCode_ = valueTypeCode::NONE;
+
+
+    // Private Member Functions
+
+        //- Assign zero, preserving the data type
+        inline void fill_zero();
+
+        //- Copy assignment
+        void deepCopy(const exprValue& rhs);
+
+
+public:
+
+    //- Runtime type information
+    ClassName("exprValue");
+
+
+    // Constructors
+
+        //- Default construct (zero-initialized) as 'none'
+        inline exprValue();
+
+        //- Copy construct (deep copy)
+        inline exprValue(const exprValue& rhs);
+
+        //- Construct from Type. Fatal for unsupported types
+        template<class Type>
+        inline explicit exprValue(const Type& val);
+
+
+    // Static Methods (valueTypeCode)
+
+        //- True if valueTypeCode is not none/invalid
+        inline static bool good
+        (
+            const expressions::valueTypeCode
+        ) noexcept;
+
+        //- True if valueTypeCode is bool/label
+        inline static bool is_integral
+        (
+            const expressions::valueTypeCode
+        ) noexcept;
+
+        //- The number of components associated with the valueTypeCode
+        inline static direction nComponents
+        (
+            const expressions::valueTypeCode
+        ) noexcept;
+
+        //- True if the specified type is supported
+        template<class Type>
+        inline static bool supportedType();
+
+
+    // Static Methods
+
+        //- Detect the type from the available tokens.
+        //  Possible ambiguity between label and scalar.
+        //  \return INVALID for unsupported type
+        static expressions::valueTypeCode peekType(const ITstream& is);
+
+        //- Read entire string as a exprValue,
+        //- skipping leading/trailing whitespace.
+        //  \return True if successful.
+        static bool read(const std::string& str, exprValue& val);
+
+
+    // Member Functions
+
+        //- The value type code
+        expressions::valueTypeCode typeCode() const noexcept
+        {
+           return typeCode_;
+        }
+
+        //- True if the value type is not none/invalid
+        inline bool good() const noexcept;
+
+        //- True if the value type is an integral (bool or label)
+        inline bool is_integral() const noexcept;
+
+        //- The number of components associated with the value type
+        inline direction nComponents() const noexcept;
+
+        //- The name for the value type. Similar to pTraits typeName
+        inline word valueTypeName() const;
+
+        //- The name for the compound token (for a List of values).
+        //- Eg, \c List\<scalar\>, \c List\<vector\> ...
+        inline word listCompoundName() const;
+
+        //- Reset to 'none'
+        void clear();
+
+        //- Guess type and read tokens (if possible)
+        //  \return True on success
+        bool read(ITstream& is);
+
+
+    // Typed Access
+
+        //- Return non-null pointer to the data element (if types match).
+        //- Can also be tested as a bool.
+        template<class Type>
+        inline const Type* isA() const noexcept;
+
+        //- Assign from type.
+        //- Returns false and sets to 'none' for unsupported types
+        template<class Type>
+        inline bool set(const Type& val);
+
+        //- Return the value. Return pTraits zero if the types mismatch
+        template<class Type>
+        inline const Type& get() const;
+
+
+    // Type-specific methods, operators
+
+    #undef  defineUnionMethods
+    #define defineUnionMethods(Type, UnusedParam)                             \
+                                                                              \
+        /*! True if value is a Type */                                        \
+        bool is_##Type() const noexcept                                       \
+        {                                                                     \
+            return (typeCode_ == exprTypeTraits<Type>::value);                \
+        }                                                                     \
+                                                                              \
+        /*! Assign from Type */                                               \
+        void operator=(const Type& val) { this->set<Type>(val); }
+
+        FOR_ALL_EXPR_VALUE_TYPES(defineUnionMethods)
+        #undef defineUnionMethods
+
+
+        //- Copy assignment
+        void operator=(const exprValue& rhs) { deepCopy(rhs); }
+
+        //- Assign from zero. Changes value but not type
+        void operator=(const Foam::zero) { fill_zero(); }
+
+
+    // Output
+
+        //- Return info proxy for printing information to a stream
+        InfoProxy<exprValue> info() const { return *this; }
+
+        //- The value as tokens. An empty list is returned for NONE.
+        tokenList tokens() const;
+
+        //- Print the (type-specific) content
+        void print(Ostream& os) const;
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace expressions
+
+
+// * * * * * * * * * * * * * * * IOstream Operators  * * * * * * * * * * * * //
+
+//- Write value to output stream in ASCII format
+Ostream& operator<<(Ostream& os, const expressions::exprValue& val);
+
+template<>
+Ostream& operator<<(Ostream& os, const InfoProxy<expressions::exprValue>&);
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#include "exprValueI.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/expressions/value/exprValueI.H b/src/OpenFOAM/expressions/value/exprValueI.H
new file mode 100644
index 0000000000..9072c9225f
--- /dev/null
+++ b/src/OpenFOAM/expressions/value/exprValueI.H
@@ -0,0 +1,213 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021-2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+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 "exprValue.H"
+
+// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
+
+inline bool Foam::expressions::exprValue::good
+(
+    const expressions::valueTypeCode valTypeCode
+) noexcept
+{
+    return
+    (
+        valTypeCode != expressions::valueTypeCode::NONE
+     && valTypeCode != expressions::valueTypeCode::INVALID
+    );
+}
+
+
+inline bool Foam::expressions::exprValue::is_integral
+(
+    const expressions::valueTypeCode valTypeCode
+) noexcept
+{
+    return
+    (
+        valTypeCode == expressions::valueTypeCode::type_bool
+     || valTypeCode == expressions::valueTypeCode::type_label
+    );
+}
+
+
+inline Foam::direction Foam::expressions::exprValue::nComponents
+(
+    const expressions::valueTypeCode valTypeCode
+) noexcept
+{
+    return expressions::Detail::nComponents(valTypeCode);
+}
+
+
+template<class Type>
+inline bool Foam::expressions::exprValue::supportedType()
+{
+    return
+    (
+        expressions::valueTypeCode::INVALID != exprTypeTraits<Type>::value
+    );
+}
+
+
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
+
+inline void Foam::expressions::exprValue::fill_zero()
+{
+    // Preserve the type
+    const auto oldType(typeCode_);
+    clear();
+    typeCode_ = oldType;
+}
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+inline Foam::expressions::exprValue::exprValue()
+{
+    clear();  // zero-initialized (type is NONE)
+}
+
+
+inline Foam::expressions::exprValue::exprValue(const exprValue& rhs)
+{
+    deepCopy(rhs);
+}
+
+
+template<class Type>
+inline Foam::expressions::exprValue::exprValue(const Type& val)
+{
+    clear();  // type: none, value: zero
+
+    set<Type>(val);
+
+    if (!good())
+    {
+        FatalErrorInFunction
+            << "Cannot construct for unsupported type: "
+            << typeid(Type).name() << endl
+            << abort(FatalError);
+    }
+}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+inline bool Foam::expressions::exprValue::good() const noexcept
+{
+    return exprValue::good(typeCode_);
+}
+
+
+inline bool Foam::expressions::exprValue::is_integral() const noexcept
+{
+    return exprValue::is_integral(typeCode_);
+}
+
+
+inline Foam::direction
+Foam::expressions::exprValue::nComponents() const noexcept
+{
+    return expressions::Detail::nComponents(typeCode_);
+}
+
+
+inline Foam::word
+Foam::expressions::exprValue::valueTypeName() const
+{
+    return Foam::name(typeCode_);
+}
+
+
+inline Foam::word Foam::expressions::exprValue::listCompoundName() const
+{
+    return
+    (
+        good()
+        // List<scalar>, List<vector> ...
+      ? word("List<" + Foam::name(typeCode_) + '>')
+      : word()
+    );
+}
+
+
+template<class Type>
+inline bool Foam::expressions::exprValue::set(const Type& val)
+{
+    const auto whichCode(exprTypeTraits<Type>::value);
+
+    if
+    (
+        whichCode == expressions::valueTypeCode::NONE
+     || whichCode == expressions::valueTypeCode::INVALID
+    )
+    {
+        clear();
+        typeCode_ = expressions::valueTypeCode::NONE;
+        return false;
+    }
+
+    data_.set<Type>(val);
+    typeCode_ = whichCode;
+    return true;
+}
+
+
+template<class Type>
+inline const Type& Foam::expressions::exprValue::get() const
+{
+    const Type* dataPtr = this->isA<Type>();
+
+    if (dataPtr)
+    {
+        return *dataPtr;
+    }
+    else
+    {
+        return pTraits<Type>::zero;
+    }
+}
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+template<class Type>
+inline const Type* Foam::expressions::exprValue::isA() const noexcept
+{
+    // NOTE: typeCode_ is *never* set to INVALID,
+    // so no false positives for unsupported types
+    return
+    (
+        (typeCode_ == exprTypeTraits<Type>::value)
+      ? data_.get<Type>()
+      : nullptr
+    );
+}
+
+
+// ************************************************************************* //