ENH: code reduction, improvements for expressions

- literal lookups only for expression strings

- code reduction for setExprFields.

- changed keyword "condition" to "fieldMask" (option -field-mask).
  This is a better description of its purpose and avoids possible
  naming ambiguities with functionObject triggers (for example)
  if we apply similar syntax elsewhere.

BUG: erroneous check in volumeExpr::parseDriver::isResultType()

- not triggered since this method is not used anywhere
  (may remove in future version)

src/OpenFOAM/expressions/exprString/exprString.C

@@ -48,20 +48,30 @@ void Foam::expressions::exprString::inplaceExpand
 
 
 Foam::expressions::exprString
-Foam::expressions::exprString::getExpression
+Foam::expressions::exprString::getEntry
 (
-    const word& name,
+    const word& key,
     const dictionary& dict,
     const bool stripComments
 )
 {
-    string orig(dict.get<string>(name));
+    exprString expr;
+    expr.readEntry(key, dict, true, stripComments);  // mandatory
 
-    // No validation
-    expressions::exprString expr;
-    expr.assign(std::move(orig));
+    return expr;
+}
 
-    inplaceExpand(expr, dict, stripComments);
+
+Foam::expressions::exprString
+Foam::expressions::exprString::getOptional
+(
+    const word& key,
+    const dictionary& dict,
+    const bool stripComments
+)
+{
+    exprString expr;
+    expr.readEntry(key, dict, false, stripComments);  // optional
 
     return expr;
 }
@@ -69,8 +79,7 @@ Foam::expressions::exprString::getExpression
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-Foam::expressions::exprString&
-Foam::expressions::exprString::expand
+void Foam::expressions::exprString::expand
 (
     const dictionary& dict,
     const bool stripComments
@@ -81,8 +90,35 @@ Foam::expressions::exprString::expand
     #ifdef FULLDEBUG
     (void)valid();
     #endif
+}
 
-    return *this;
+
+void Foam::expressions::exprString::trim()
+{
+    stringOps::inplaceTrim(*this);
+}
+
+
+bool Foam::expressions::exprString::readEntry
+(
+    const word& keyword,
+    const dictionary& dict,
+    bool mandatory,
+    const bool stripComments
+)
+{
+    const bool ok = dict.readEntry(keyword, *this, keyType::LITERAL, mandatory);
+
+    if (ok && !empty())
+    {
+        this->expand(dict, stripComments);  // strip comments
+    }
+    else
+    {
+        clear();
+    }
+
+    return ok;
 }
 
 

src/OpenFOAM/expressions/exprString/exprString.H

@@ -135,13 +135,22 @@ public:
 
         //- Get and expand expression with dictionary entries,
         //- optionally strip C/C++ comments from the input.
-        //
         // Expansion behaviour as per inplaceExpand
-        static exprString getExpression
+        static exprString getEntry
         (
-            const word& name,
+            const word& keyword,  //!< Lookup key. Uses LITERAL (not REGEX)
             const dictionary& dict,
-            const bool stripComments = false
+            const bool stripComments = true
+        );
+
+        //- Get and expand expression with dictionary entries,
+        //- optionally strip C/C++ comments from the input.
+        // Expansion behaviour as per inplaceExpand
+        static exprString getOptional
+        (
+            const word& keyword,  //!< Lookup key. Uses LITERAL (not REGEX)
+            const dictionary& dict,
+            const bool stripComments = true
         );
 
         //- Copy convert string to exprString.
@@ -155,17 +164,26 @@ public:
 
     // Member Functions
 
-        //- Inplace expansion with dictionary variables,
-        //- and strip C/C++ comments from the input
-        exprString& expand
-        (
-            const dictionary& dict,
-            const bool stripComments = true
-        );
-
         //- Check for unexpanded '$' entries. Fatal if any exist.
         inline bool valid() const;
 
+        //- Inplace expansion with dictionary variables,
+        //- and strip C/C++ comments from the input
+        void expand(const dictionary& dict, const bool stripComments = true);
+
+        //- Inplace trim leading and trailing whitespace
+        void trim();
+
+        //- Read/expand entry with dictionary variables,
+        //- and strip C/C++ comments from the input
+        bool readEntry
+        (
+            const word& keyword,  //!< Lookup key. Uses LITERAL (not REGEX)
+            const dictionary& dict,
+            bool mandatory = true,
+            const bool stripComments = true
+        );
+
 
     // Member Operators