Class Compare_handles_with_or_without_timestamps to replace hacks

Previously, each file was using its own implementation of the "compare
handle" function object. This commits adds a new class
`Compare_handles_with_or_without_timestamps` that checks the presence of
`Has_timestamp` in the pointed type, and provides a different
`operator()` depending on that.

Mesh_3/include/CGAL/Mesh_3/Detect_features_in_polyhedra.h

@@ -24,25 +24,12 @@
 
 #include <CGAL/Kernel/global_functions_3.h>
 #include <CGAL/Mesh_3/Detect_features_in_polyhedra_fwd.h>
+#include <CGAL/Compare_handles_with_or_without_timestamps.h>
 #include <set>
 
 namespace CGAL {
 namespace Mesh_3 {
 
-struct Detect_features_less
-{
-  template<typename Handle>
-  bool operator()(const Handle& h1, const Handle& h2) const
-  {
-    typedef typename std::iterator_traits<Handle>::value_type Type;
-    typedef typename boost::mpl::if_c<
-        CGAL::internal::Has_timestamp<Type>::value,
-        CGAL_with_time_stamp<Handle>,
-        CGAL_no_time_stamp<Handle> >::type    Comparator;
-    return Comparator::less(h1, h2);
-  }
-};
-
 template <typename Polyhedron>
 void detect_features(Polyhedron& p,
                      typename Polyhedron::Traits::FT angle_in_deg)
@@ -68,9 +55,10 @@ public:
   typedef typename Polyhedron::Halfedge         Halfedge;
   typedef typename Polyhedron::Facet            Facet;
   typedef typename Facet::Patch_id              Patch_id;
+  typedef CGAL::Compare_handles_with_or_without_timestamps Compare_handles;
   
-  typedef std::set<Facet_handle, Detect_features_less> Facet_handle_set;
-  typedef std::set<Halfedge_handle, Detect_features_less> He_handle_set;
+  typedef std::set<Facet_handle, Compare_handles> Facet_handle_set;
+  typedef std::set<Halfedge_handle, Compare_handles> He_handle_set;
   
 public:
   Detect_features_in_polyhedra() : current_surface_index_(1) {}

Mesh_3/include/CGAL/Mesh_3/Detect_polylines_in_polyhedra.h

@@ -23,7 +23,7 @@
 #define CGAL_MESH_3_DETECT_POLYLINES_IN_POLYHEDRA_H
 
 #include <CGAL/Mesh_3/Detect_polylines_in_polyhedra_fwd.h>
-#include <CGAL/Has_timestamp.h>
+#include <CGAL/Compare_handles_with_or_without_timestamps.h>
 #include <CGAL/Default.h>
 
 #include <algorithm>
@@ -32,40 +32,6 @@
 
 namespace CGAL { namespace Mesh_3 {
 
-template <typename Handle>
-struct CGAL_with_time_stamp
-{
-public:
-  static bool less(Handle h1, Handle h2)
-  {
-    return h1->time_stamp() < h2->time_stamp();
-  }
-};
-
-template <typename Handle>
-struct CGAL_no_time_stamp
-{
-public:
-  static bool less(Handle h1, Handle h2)
-  {
-    return &*h1 < &*h2;
-  }
-};
-
-struct Detect_polyline_less
-{
-  template<typename Handle>
-  bool operator()(const Handle& h1, const Handle& h2) const
-  {
-    typedef typename std::iterator_traits<Handle>::value_type Type;
-    typedef typename boost::mpl::if_c<
-        CGAL::internal::Has_timestamp<Type>::value,
-        CGAL_with_time_stamp<Handle>,
-        CGAL_no_time_stamp<Handle> >::type    Comparator;
-    return Comparator::less(h1, h2);
-  }
-};
-
 template <typename Polyhedron>
 struct Detect_polylines {
   typedef typename Polyhedron::Traits Geom_traits;
@@ -75,13 +41,14 @@ struct Detect_polylines {
   typedef typename Polyhedron::Vertex_const_handle Vertex_const_handle;
   typedef typename Polyhedron::Vertex_handle Vertex_handle;
   typedef typename Polyhedron::size_type size_type;
+  typedef CGAL::Compare_handles_with_or_without_timestamps Compare_handles;
 
-  typedef std::set<Vertex_handle, Detect_polyline_less> Vertices_set;
+  typedef std::set<Vertex_handle, Compare_handles> Vertices_set;
   typedef std::map<Vertex_handle, 
                    size_type,                    
-                   Detect_polyline_less> Vertices_counter;
+                   Compare_handles> Vertices_counter;
 
-  typedef std::set<Halfedge_handle, Detect_polyline_less> Feature_edges_set;
+  typedef std::set<Halfedge_handle, Compare_handles> Feature_edges_set;
 
   Feature_edges_set edges_to_consider;
   Vertices_set corner_vertices;
@@ -143,7 +110,7 @@ struct Detect_polylines {
   static Halfedge_handle canonical(Halfedge_handle he)
   {
     const Halfedge_handle& op = he->opposite();
-    if(Detect_polyline_less()(he, op))
+    if(Compare_handles()(he, op))
       return he;
     else 
       return op;

STL_Extension/include/CGAL/Compare_handles_with_or_without_timestamps.h

@@ -0,0 +1,55 @@
+// Copyright (c) 2017 GeometryFactory Sarl (France)
+// All rights reserved.
+//
+// This file is part of CGAL (www.cgal.org); you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation; either version 3 of the License,
+// or (at your option) any later version.
+//
+// Licensees holding a valid commercial license may use this file in
+// accordance with the commercial license agreement provided with the software.
+//
+// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
+// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+//
+//
+//
+// Author(s)     : Laurent Rineau
+
+#ifndef CGAL_COMPARE_HANDLES_WITH_OR_WITHOUT_TIMESTAMPS_H
+#define CGAL_COMPARE_HANDLES_WITH_OR_WITHOUT_TIMESTAMPS_H
+
+#include <CGAL/Has_timestamp.h>
+#include <CGAL/tags.h>
+#include <iterator>
+
+namespace CGAL {
+
+struct Compare_handles_with_or_without_timestamps
+{
+  template<typename Handle>
+  bool operator()(const Handle h1, const Handle h2) const
+  {
+    typedef typename std::iterator_traits<Handle>::value_type Type;
+    return less(h1, h2,
+                Boolean_tag<CGAL::internal::Has_timestamp<Type>::value>());
+  }
+
+  template<typename Handle>
+  bool less(const Handle h1, const Handle h2, Tag_false) const
+  {
+    return &*h1 < &*h2;
+  }
+
+  template<typename Handle>
+  bool less(const Handle h1, const Handle h2, Tag_true) const
+  {
+    if(h1 == Handle())      return (h2 != Handle());
+    else if(h2 == Handle()) return false;
+    else                    return h1->time_stamp() < h2->time_stamp();
+  }
+};
+
+} // end namespace CGAL
+
+#endif // CGAL_COMPARE_HANDLES_WITH_OR_WITHOUT_TIMESTAMPS_H

STL_Extension/include/CGAL/Time_stamper.h

@@ -16,11 +16,11 @@
 //
 // Author(s)     : Jane Tournois
 
-#include <CGAL/Has_timestamp.h>
-
 #ifndef CGAL_TIME_STAMPER_H
 #define CGAL_TIME_STAMPER_H
 
+#include <CGAL/Has_timestamp.h>
+
 namespace CGAL {
 
 template <typename T>