ENH: improvements to labelRange const_iterator

- inherit from std::iterator to obtain the full STL typedefs, meaning
  that std::distance works and the following is now possible:

      labelRange range(100, 1500);
      scalarList list(range.begin(), range.end());

  --
  Note that this does not work (mismatched data-types):

      scalarList list = identity(12345);

  But this does, since the *iter promotes label to scalar:

      labelList ident = identity(12345);
      scalarList list(ident.begin(), ident.end());

  It is however more than slightly wasteful to create a labelList
  just for initializing a scalarList. An alternative could be a
  a labelRange for the same purpose.

      labelRange ident = labelRange::identity(12345);
      scalarList list(ident.begin(), ident.end());

  Or this
      scalarList list
      (
          labelRange::null.begin(),
          labelRange::identity(12345).end()
      );

applications/test/List/Test-List.C

@@ -42,6 +42,7 @@ See also
 #include "vector.H"
 
 #include "labelRange.H"
+#include "scalarList.H"
 #include "ListOps.H"
 #include "SubList.H"
 
@@ -144,6 +145,18 @@ int main(int argc, char *argv[])
 
         labelList longLabelList = identity(15);
 
+        // This does not work:
+        // scalarList slist = identity(15);
+        //
+        // More writing, but does work:
+        scalarList slist
+        (
+            labelRange::null.begin(),
+            labelRange::identity(15).end()
+        );
+
+        Info<<"scalar identity:" << flatOutput(slist) << endl;
+
         Info<< "labels (contiguous=" << contiguous<label>() << ")" << nl;
 
         Info<< "normal: " << longLabelList << nl;
@@ -220,7 +233,32 @@ int main(int argc, char *argv[])
         }
         Info<< "sub-sorted: " << flatOutput(longLabelList) << nl;
 
-        // Info<<"Slice=" << longLabelList[labelRange(23,5)] << nl;
+        // construct from a label-range
+        labelRange range(25,15);
+
+        labelList ident(range.begin(), range.end());
+        Info<<"range-list (label)=" << ident << nl;
+
+        List<scalar> sident(range.begin(), range.end());
+        Info<<"range-list (scalar)=" << sident << nl;
+
+        // Sub-ranges also work
+        List<scalar> sident2(range(3), range(10));
+        Info<<"range-list (scalar)=" << sident2 << nl;
+
+        // VERY BAD IDEA: List<scalar> sident3(range(10), range(3));
+
+        // This doesn't work, and don't know what it should do anyhow
+        // List<vector> vident(range.begin(), range.end());
+        // Info<<"range-list (vector)=" << vident << nl;
+
+        // Even weird things like this
+        List<scalar> sident4
+        (
+            labelRange().begin(),
+            labelRange::identity(8).end()
+        );
+        Info<<"range-list (scalar)=" << sident4 << nl;
     }
 
     wordReList reLst;

applications/test/labelRanges/Test-labelRanges.C

@@ -58,7 +58,7 @@ int main(int argc, char *argv[])
         Info<<"test sorting" << endl;
         DynamicList<labelRange> list1(10);
         list1.append(labelRange(25, 8));
-        list1.append(labelRange(0, 10));
+        list1.append(labelRange::identity(8));
         list1.append(labelRange(15, 5));
         list1.append(labelRange(50, -10));
 

src/OpenFOAM/primitives/ranges/labelRange/labelRange.C

@@ -34,6 +34,8 @@ namespace Foam
 int labelRange::debug(debug::debugSwitch("labelRange", 0));
 }
 
+const Foam::labelRange Foam::labelRange::null;
+
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 

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

@@ -35,6 +35,7 @@ SourceFiles
 #define labelRange_H
 
 #include "label.H"
+#include <iterator>
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -63,26 +64,32 @@ class labelRange
 
 public:
 
-    static int debug;
+    // Static Data Members
+
+        static int debug;
+
+        //- An empty range with start=0, size=0.
+        static const labelRange null;
+
 
     // STL type definitions similar to what UList has
 
         //- Type of values the range contains
         typedef label value_type;
 
-        //- The type that can represent the difference between two iterators
-        typedef label difference_type;
-
         //- The type that can represent the size of the range
         typedef label size_type;
 
+        // Forward declaration
+        class const_iterator;
+
 
     // Constructors
 
         //- An empty range with zero for start/size.
         inline labelRange();
 
-        //- Construct a range from start and size, enforcing non-negative size.
+        //- Construct a range from start/size, enforcing non-negative size.
         //  Optionally adjust the start to avoid any negative indices.
         inline labelRange
         (
@@ -95,6 +102,12 @@ public:
         labelRange(Istream& is);
 
 
+    // Static Member Functions
+
+        //- An identity range with range[i] == i.
+        inline static labelRange identity(const label len);
+
+
     // Member Functions
 
         //- Adjust start position
@@ -184,6 +197,9 @@ public:
         //- Return element in the range, no bounds checking
         inline label operator[](const label localIndex) const;
 
+        //- Return const_iterator to element in the range
+        inline const_iterator operator()(const label localIndex) const;
+
         //- Increase the size by 1.
         inline label operator++();
         inline label operator++(int);
@@ -197,21 +213,30 @@ public:
 
         //- Forward iterator with const access
         class const_iterator
+        :
+            public std::iterator
+            <
+                std::input_iterator_tag,
+                label,
+                label,
+                const label*,
+                const label&
+            >
         {
-            //- The current label (not the local index)
-            label index_;
+            //- The current (global) value
+            label value_;
 
         public:
 
           // Constructors
 
             //- Construct from range at given local index.
-            //  A negative index signals the 'end' position
-            inline const_iterator(const labelRange* range, const label i = 0);
+            //  A negative index is invalid and corresponds to the 'end'
+            inline const_iterator(const labelRange* range, const label i=0);
 
           // Member operators
 
-            //- Return the current label
+            //- Return the current (global) value
             inline label operator*() const;
 
             inline const_iterator& operator++();

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

@@ -64,7 +64,7 @@ inline Foam::labelRange::const_iterator::const_iterator
     const label i
 )
 :
-    index_
+    value_
     (
         range->start()
       + ((i < 0 || i > range->size()) ? range->size() : i)
@@ -74,14 +74,14 @@ inline Foam::labelRange::const_iterator::const_iterator
 
 inline Foam::label Foam::labelRange::const_iterator::operator*() const
 {
-    return index_;
+    return value_;
 }
 
 
 inline Foam::labelRange::const_iterator&
 Foam::labelRange::const_iterator::operator++()
 {
-    ++index_;
+    ++value_;
     return *this;
 }
 
@@ -90,7 +90,7 @@ inline Foam::labelRange::const_iterator
 Foam::labelRange::const_iterator::operator++(int)
 {
     const_iterator old = *this;
-    ++index_;
+    ++value_;
     return old;
 }
 
@@ -100,7 +100,7 @@ inline bool Foam::labelRange::const_iterator::operator==
     const const_iterator& iter
 ) const
 {
-    return (this->index_ == iter.index_);
+    return (this->value_ == iter.value_);
 }
 
 
@@ -109,7 +109,7 @@ inline bool Foam::labelRange::const_iterator::operator!=
     const const_iterator& iter
 ) const
 {
-    return (this->index_ != iter.index_);
+    return (this->value_ != iter.value_);
 }
 
 
@@ -139,6 +139,12 @@ inline const Foam::labelRange::const_iterator Foam::labelRange::cend() const
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
+inline Foam::labelRange Foam::labelRange::identity(const label len)
+{
+    return labelRange(0, len);
+}
+
+
 inline void Foam::labelRange::setStart(const label i)
 {
     start_ = i;
@@ -264,6 +270,13 @@ inline Foam::label Foam::labelRange::operator[](const label localIndex) const
 }
 
 
+inline Foam::labelRange::const_iterator
+Foam::labelRange::operator()(const label localIndex) const
+{
+    return const_iterator(this, localIndex);
+}
+
+
 inline Foam::label Foam::labelRange::operator++()
 {
     return ++size_;