add example for unordered_set

Arrangement_on_surface_2/doc/Arrangement_on_surface_2/CGAL/Arrangement_2.h

@@ -370,6 +370,8 @@ counterparts. `Vertex_iterator`, `Halfedge_iterator`, and
 the handles appear in function parameter lists, the respective
 iterators can be passed as well.
 
+All handles are model of `LessThanComparable` and `Hashable`.
+
 */
 /// @{
 

STL_Extension/doc/STL_Extension/STL_Extension.txt

@@ -130,6 +130,13 @@ looking up keys whose type may differ from `Type`, as long as users supply
 a comparison functor `CompareKey`, between the keys and set elements;
 and catenating and splitting sets.
 
+\section stl_hash Hashing
+
+For handles and indices of vertices, halfedges, faces, etc., we provide specializations of `boost::hash<T>` and `std::hash<T>, so that they can be used with classes such as `boost::unordered_map`.
+
+\cgalExample{STL_Extension/unordered_map.cpp}
+
+
 \section stl_polyobject Polymorphic Object
 
 The class `Object` can store an object of whatever other type.

STL_Extension/doc/STL_Extension/dependencies

@@ -3,3 +3,4 @@ Circulator
 Number_types
 Kernel_23
 Miscellany
+Surface_mesh

STL_Extension/doc/STL_Extension/examples.txt

@@ -3,4 +3,5 @@
 \example STL_Extension/in_place_list_prog.cpp
 \example STL_Extension/min_element_if_example.cpp
 \example STL_Extension/min_max_element_example.cpp
+\example STL_Extension/unordered_map.cpp
 */

STL_Extension/examples/STL_Extension/unordered_map.cpp

@@ -0,0 +1,19 @@
+
+#include <CGAL/Simple_cartesian.h>
+#include <CGAL/Surface_mesh.h>
+#include <boost/unordered_map.hpp>
+
+
+typedef CGAL::Simple_cartesian<double>  Kernel;
+typedef Kernel::Point_3                 Point_3;
+typedef CGAL::Surface_mesh<Point_3>     Mesh;
+typedef boost::graph_traits<Mesh>::vertex_descriptor vertex_descriptor;
+
+int main()
+{ 
+  boost::unordered_map<vertex_descriptor, int> bum;
+  Mesh mesh;
+  vertex_descriptor vd  = mesh.add_vertex();
+  bum[vd] = 7812;
+  return 0;
+}

Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h

@@ -130,6 +130,8 @@ namespace CGAL {
 
     /// This class represents a vertex.
     /// \cgalModels `Index`
+    /// \cgalModels `LessThanComparable`
+    /// \cgalModels `Hashable`
     /// \sa `Halfedge_index`, `Edge_index`, `Face_index`
     class SM_Vertex_index
  : public SM_Index<SM_Vertex_index>
@@ -149,6 +151,8 @@ namespace CGAL {
 
     /// This class represents a halfedge.
     /// \cgalModels `Index`
+    /// \cgalModels `LessThanComparable`
+    /// \cgalModels `Hashable`
     /// \sa `Vertex_index`, `Edge_index`, `Face_index`
     class SM_Halfedge_index
       : public SM_Index<SM_Halfedge_index>
@@ -168,6 +172,8 @@ namespace CGAL {
 
     /// This class represents a face
     /// \cgalModels `Index`
+    /// \cgalModels `LessThanComparable`
+    /// \cgalModels `Hashable`
     /// \sa `Vertex_index`, `Halfedge_index`, `Edge_index`
     class SM_Face_index
       : public SM_Index<SM_Face_index>
@@ -187,6 +193,8 @@ namespace CGAL {
 
     /// This class represents an edge.
     /// \cgalModels `Index`
+    /// \cgalModels `LessThanComparable`
+    /// \cgalModels `Hashable`
     /// \sa `Vertex_index`, `Halfedge_index`, `Face_index`
     class SM_Edge_index
     {