diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_circular_line_arc_traits_2.h b/Arrangement_on_surface_2/include/CGAL/Arr_circular_line_arc_traits_2.h
index 4efc598b81d..c48fa96917c 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_circular_line_arc_traits_2.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_circular_line_arc_traits_2.h
@@ -339,7 +339,6 @@ namespace CGAL {
 
      template <class CircularKernel>
     class Variant_Construct_min_vertex_2
-      <const typename CircularKernel::Circular_arc_point_2&>
     {
       typedef typename CircularKernel::Circular_arc_point_2
                                                   Circular_arc_point_2;
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_trapezoid.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_trapezoid.h
index 44834852a2b..d8a775c4179 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_trapezoid.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_active_trapezoid.h
@@ -459,12 +459,12 @@ private:
 
     Td_map_item item (*this);
 
-    if (ptr()->rb.which() != 0)
+    if (ptr()->rb.index() != 0)
     {
       Self tr(std::get<Self>(rb()));
       tr.set_lb(item);
     }
-    if (ptr()->rt.which() != 0)
+    if (ptr()->rt.index() != 0)
     {
       Self tr(std::get<Self>(rt()));
       tr.set_lt(item);
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_traits.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_traits.h
index 59a3dd7f6b6..391fb264658 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_traits.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Td_traits.h
@@ -957,13 +957,13 @@ public:
   //returns true if the trapezoid is a curve
   bool is_empty_item(const Td_map_item& tr) const
   {
-    return (tr.which() == 0);
+    return (tr.index() == 0);
   }
 
   //returns true if the trapezoid is a point or a curve
   bool is_trapezoid(const Td_map_item& tr) const
   {
-    switch (tr.which())
+    switch (tr.index())
     {
     case TD_ACTIVE_TRAPEZOID:
     case TD_INACTIVE_TRAPEZOID:
@@ -976,7 +976,7 @@ public:
   //returns true if the map item is a vertex
   bool is_td_vertex(const Td_map_item& tr) const
   {
-    switch (tr.which())
+    switch (tr.index())
     {
     case TD_ACTIVE_VERTEX:
     case TD_ACTIVE_FICTITIOUS_VERTEX:
@@ -991,7 +991,7 @@ public:
   //returns true if the map item is an edge
   bool is_td_edge(const Td_map_item& tr) const
   {
-    switch (tr.which())
+    switch (tr.index())
     {
     case TD_ACTIVE_EDGE:
     case TD_INACTIVE_EDGE:
@@ -1004,7 +1004,7 @@ public:
   //returns true if the map item is an edge
   bool is_td_trapezoid(const Td_map_item& tr) const
   {
-    switch (tr.which())
+    switch (tr.index())
     {
     case TD_ACTIVE_TRAPEZOID:
     case TD_INACTIVE_TRAPEZOID:
@@ -1017,7 +1017,7 @@ public:
   //returns true if the trapezoid is a curve
   bool is_fictitious_vertex(const Td_map_item& tr) const
   {
-    switch (tr.which())
+    switch (tr.index())
     {
     case TD_ACTIVE_FICTITIOUS_VERTEX:
     case TD_INACTIVE_FICTITIOUS_VERTEX:
@@ -1030,7 +1030,7 @@ public:
   //returns true if the trapezoid is a curve
   bool is_active(const Td_map_item& tr) const
   {
-    switch (tr.which())
+    switch (tr.index())
     {
       case TD_ACTIVE_TRAPEZOID:
       case TD_ACTIVE_EDGE:
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Trapezoidal_decomposition_2.h b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Trapezoidal_decomposition_2.h
index be7d7ac72b3..3888b097bb8 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Trapezoidal_decomposition_2.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_point_location/Trapezoidal_decomposition_2.h
@@ -717,6 +717,7 @@ public:
   /*! A visitor to set the cw halfedge of a vertex node.
    */
   class set_cw_he_visitor
+  {
   public:
     set_cw_he_visitor(Halfedge_const_handle he) : m_cw_he(he) {}
 
@@ -735,6 +736,7 @@ public:
   /*! A visitor to reset the cw halfedge of a vertex node.
    */
   class reset_cw_he_visitor
+  {
   public:
     void operator()(Td_active_vertex& t) const { t.reset_cw_he(); }
 
diff --git a/Hyperbolic_triangulation_2/include/CGAL/Hyperbolic_triangulation_face_base_2.h b/Hyperbolic_triangulation_2/include/CGAL/Hyperbolic_triangulation_face_base_2.h
index 32d730aab7c..724f45794e6 100644
--- a/Hyperbolic_triangulation_2/include/CGAL/Hyperbolic_triangulation_face_base_2.h
+++ b/Hyperbolic_triangulation_2/include/CGAL/Hyperbolic_triangulation_face_base_2.h
@@ -23,7 +23,7 @@ namespace CGAL {
 
 class Hyperbolic_data
 {
-  typedef boost::int8_t Id;
+  typedef std::int8_t Id;
 
 private:
   // - 2 for infinite face
diff --git a/SMDS_3/include/CGAL/IO/output_to_vtu.h b/SMDS_3/include/CGAL/IO/output_to_vtu.h
index 37cd018570f..863bba2cebb 100644
--- a/SMDS_3/include/CGAL/IO/output_to_vtu.h
+++ b/SMDS_3/include/CGAL/IO/output_to_vtu.h
@@ -314,7 +314,7 @@ void output_to_vtu_with_attributes(std::ostream& os,
   os << "    <CellData Scalars=\""<<attributes.front().first<<"\">\n";
   for(std::size_t i = 0; i< attributes.size(); ++i)
   {
-    switch(attributes[i].second.which()){
+    switch(attributes[i].second.index()){
     case 0:
       write_attribute_tag(os,attributes[i].first, *std::get<const std::vector<double>* >(attributes[i].second), binary,offset);
       break;
@@ -334,7 +334,7 @@ void output_to_vtu_with_attributes(std::ostream& os,
     write_c3t3_points(os,tr,V); // fills V if the mode is BINARY
     write_cells(os,c3t3,V);
     for(std::size_t i = 0; i< attributes.size(); ++i)
-      switch(attributes[i].second.which()){
+      switch(attributes[i].second.index()){
       case 0:
         write_attributes(os, *std::get<const std::vector<double>* >(attributes[i].second));
         break;
diff --git a/SMDS_3/include/CGAL/SMDS_3/internal/Handle_IO_for_pair_of_int.h b/SMDS_3/include/CGAL/SMDS_3/internal/Handle_IO_for_pair_of_int.h
index 977909a463d..87d4e5863d5 100644
--- a/SMDS_3/include/CGAL/SMDS_3/internal/Handle_IO_for_pair_of_int.h
+++ b/SMDS_3/include/CGAL/SMDS_3/internal/Handle_IO_for_pair_of_int.h
@@ -61,7 +61,7 @@ class Output_rep<std::variant<int,
 public:
   Output_rep(const Variant& v) : v(v) {}
   std::ostream& operator()( std::ostream& out) const {
-    if(v.which() == 1) {
+    if(v.index() == 1) {
       out << IO::oformat(std::get<std::pair<int, int> >(v));
     } else {
       out << std::get<int>(v);