STYLE: rename toLabel, toLabelRange classes -> labelOp, labelRangeOp

- make purpose as functors _slightly_ clearer.

- base definition removed for stricter enforcement of the specialization
  requirement.

applications/test/List/Test-List.C

@@ -426,7 +426,7 @@ int main(int argc, char *argv[])
             auto output = ListOps::create<label>
             (
                 input,
-                toLabel<int64_t>()
+                labelOp<int64_t>()
             );
             Info<< "label (from int64): " << flatOutput(output) << endl;
         }
@@ -438,7 +438,7 @@ int main(int argc, char *argv[])
             auto output = ListOps::create<label>
             (
                 input,
-                toLabel<int32_t>()
+                labelOp<int32_t>()
             );
             Info<< "label (from int32): " << flatOutput(output) << endl;
         }

applications/utilities/mesh/manipulation/checkMesh/checkGeometry.C

@@ -1010,7 +1010,7 @@ Foam::label Foam::checkGeometry
                             ListOps::create<label>
                             (
                                 UPstream::procID(UPstream::worldComm),
-                                toLabel<int>()  // int -> label
+                                labelOp<int>()  // int -> label
                             ),
                             ami.srcWeightsSum(),
                             mergedWeights
@@ -1064,7 +1064,7 @@ Foam::label Foam::checkGeometry
                             ListOps::create<label>
                             (
                                 UPstream::procID(UPstream::worldComm),
-                                toLabel<int>()  // int -> label
+                                labelOp<int>()  // int -> label
                             ),
                             ami.tgtWeightsSum(),
                             mergedWeights

applications/utilities/mesh/manipulation/moveDynamicMesh/moveDynamicMesh.C

@@ -87,7 +87,7 @@ void writeWeights
         ListOps::create<label>
         (
             UPstream::procID(UPstream::worldComm),
-            toLabel<int>()  // int -> label
+            labelOp<int>()  // int -> label
         ),
         wghtSum,
         mergedWeights

src/OpenFOAM/containers/Lists/ListOps/ListOps.H

@@ -478,7 +478,7 @@ void setValue
 //  auto labels = ListOps::create<label>
 //  (
 //      ints,
-//      toLabel<int>()
+//      labelOp<int>()
 //  );
 //
 //  auto vectors = ListOps::create<vector>

src/OpenFOAM/meshes/polyMesh/polyPatches/polyPatch/polyPatch.H

@@ -426,9 +426,9 @@ public:
 
 // Global Functions
 
-//- Get the labelRange for a polyPatch
+//- The labelRange of a polyPatch
 template<>
-struct toLabelRange<polyPatch>
+struct labelRangeOp<polyPatch>
 {
     labelRange operator()(const polyPatch& pp) const
     {

src/OpenFOAM/primitives/ints/label/label.H

@@ -122,15 +122,16 @@ inline label component(const label l, const direction)
 
 
 /*---------------------------------------------------------------------------*\
-                          Struct toLabel Declaration
+                          Struct labelOp Declaration
 \*---------------------------------------------------------------------------*/
 
-//- Conversion to label structure
-template<class Type> struct toLabel {};
+//- Conversion/extraction to label operation
+//  Specialization of this shall provide a corresponding \c operator().
+template<class> struct labelOp;
 
 //- Convert (likely promote) from int32_t to label
 template<>
-struct toLabel<int32_t>
+struct labelOp<int32_t>
 {
     constexpr label operator()(const int32_t& val) const noexcept
     {
@@ -141,7 +142,7 @@ struct toLabel<int32_t>
 
 //- Convert (possibly truncate) from int64_t to label
 template<>
-struct toLabel<int64_t>
+struct labelOp<int64_t>
 {
     constexpr label operator()(const int64_t& val) const noexcept
     {

src/OpenFOAM/primitives/ranges/labelRange/labelRange.H

@@ -25,7 +25,7 @@ Class
     Foam::labelRange
 
 Description
-    A range of labels defined by a start and a size.
+    An range or interval of labels defined by a start and a size.
 
 SourceFiles
     labelRange.C
@@ -248,14 +248,14 @@ public:
 
         public:
 
-          // Constructors
+        // Constructors
 
             //- Construct from range at given local index.
             //  If the local index is out of range (eg, negaative),
             //  this creates the 'end' iterator
             inline const_iterator(const labelRange* range, const label i=0);
 
-          // Member operators
+        // Member Operators
 
             //- Return the current (global) value
             inline label operator*() const;
@@ -293,8 +293,20 @@ public:
 
 // Global Functions
 
-//- Conversion to labelRange operations
-template<class Type> struct toLabelRange {};
+//- Conversion/extraction to labelRange operation (functor).
+//  Specializations shall provide a corresponding \c operator().
+//  For example,
+//  \code
+//  template<>
+//  struct labelRangeOp<polyPatch>
+//  {
+//      labelRange operator()(const polyPatch& pp) const
+//      {
+//          return labelRange(pp.start(), pp.size());
+//      }
+//  };
+//  \endcode
+template<class> struct labelRangeOp;
 
 
 // Global Operators

src/surfMesh/surfZone/surfZone/surfZone.H

@@ -183,9 +183,9 @@ public:
 
 // Global Functions
 
-//- Get the labelRange for a surfZone
+//- The labelRange of a surfZone
 template<>
-struct toLabelRange<surfZone>
+struct labelRangeOp<surfZone>
 {
     labelRange operator()(const surfZone& zone) const
     {