circular kernel 2 result_of to decltype

Circular_kernel_2/include/CGAL/Circular_arc_2.h

@@ -22,7 +22,6 @@
 
 
 #include <CGAL/config.h>
-#include <CGAL/result_of.h>
 #include <CGAL/Bbox_2.h>
 #include <CGAL/enum.h>
 namespace CGAL {
@@ -107,25 +106,25 @@ public:
   {}
 
 
-  typename cpp11::result_of<typename R::Construct_circular_source_vertex_2(Circular_arc_2)>::type
+  decltype(auto)
   source() const
   {
     return typename R::Construct_circular_source_vertex_2()(*this);
   }
 
-  typename cpp11::result_of<typename R::Construct_circular_target_vertex_2(Circular_arc_2)>::type
+  decltype(auto)
   target() const
   {
     return typename R::Construct_circular_target_vertex_2()(*this);
   }
 
-  typename cpp11::result_of<typename R::Construct_circular_min_vertex_2(Circular_arc_2)>::type
+  decltype(auto)
   left() const
   {
     return typename R::Construct_circular_min_vertex_2()(*this);
   }
 
-  typename cpp11::result_of<typename R::Construct_circular_max_vertex_2(Circular_arc_2)>::type
+  decltype(auto)
   right() const
   {
     return typename R::Construct_circular_max_vertex_2()(*this);
@@ -141,19 +140,19 @@ public:
     return typename R::Is_y_monotone_2()(*this);
   }
 
-  typename cpp11::result_of<typename R::Construct_circle_2(Circular_arc_2)>::type
+  decltype(auto)
   supporting_circle() const
   {
     return typename R::Construct_circle_2()(*this);
   }
 
-  typename cpp11::result_of<typename R::Construct_center_2(Circular_arc_2)>::type
+  decltype(auto)
   center() const
   {
     return typename R::Construct_center_2()(*this);
   }
 
-  typename cpp11::result_of<typename R::Compute_squared_radius_2( Circular_arc_2)>::type
+  decltype(auto)
   squared_radius() const
   {
     return typename R::Compute_squared_radius_2()(*this);

Circular_kernel_2/include/CGAL/Circular_arc_point_2.h

@@ -21,7 +21,6 @@
 #include <CGAL/license/Circular_kernel_2.h>
 
 
-#include <CGAL/result_of.h>
 #include <CGAL/Bbox_2.h>
 #include <CGAL/enum.h>
 
@@ -72,15 +71,13 @@ public:
     : RCircular_arc_point_2(typename R::Construct_circular_arc_point_2()(p))
   {}
 
-  typename
-  cpp11::result_of<typename R::Compute_circular_x_2(Circular_arc_point_2)>::type
+  decltype(auto)
   x() const
   {
     return typename R::Compute_circular_x_2()(*this);
   }
 
-  typename
-  cpp11::result_of<typename R::Compute_circular_y_2(Circular_arc_point_2)>::type
+  decltype(auto)
   y() const
   {
     return typename R::Compute_circular_y_2()(*this);

Circular_kernel_2/include/CGAL/Circular_kernel_2/Circular_arc_2.h

@@ -639,13 +639,13 @@ public:
        return _support;
     }
 
-    typename cpp11::result_of<typename CK::Construct_center_2(Circle_2)>::type
+    decltype(auto)
     center() const
     {
        return supporting_circle().center();
     }
 
-    typename cpp11::result_of<typename CK::Compute_squared_radius_2(Circle_2)>::type
+    decltype(auto)
     squared_radius() const
     {
        return supporting_circle().squared_radius();

Circular_kernel_2/include/CGAL/Circular_kernel_2/function_objects_polynomial_circular.h

@@ -1307,7 +1307,7 @@ namespace CircularFunctors {
       typedef typename cpp11::result_of<LK_Compute_squared_radius_2(Circle_2)>::type type;
     };
 
-    typename cpp11::result_of<LK_Compute_squared_radius_2(Circle_2)>::type
+    decltype(auto)
     operator()( const Circle_2& c) const
     { return LK_Compute_squared_radius_2()(c); }
 
@@ -1320,7 +1320,7 @@ namespace CircularFunctors {
     FT operator()( const Point_2& p, const Point_2& q, const Point_2& r) const
     { return LK_Compute_squared_radius_2()(p, q, r); }
 
-    typename cpp11::result_of<LK_Compute_squared_radius_2(Circle_2)>::type
+    decltype(auto)
     operator()(const Circular_arc_2& c) const
     { return c.rep().squared_radius(); }
 

Circular_kernel_2/include/CGAL/Line_arc_2.h

@@ -21,7 +21,6 @@
 #include <CGAL/license/Circular_kernel_2.h>
 
 
-#include <CGAL/result_of.h>
 #include <CGAL/Bbox_2.h>
 
 namespace CGAL {
@@ -91,25 +90,25 @@ public:
      : RLine_arc_2(a)
    {}
 
-  typename cpp11::result_of< typename R::Construct_circular_source_vertex_2(Line_arc_2)>::type
+  decltype(auto)
     source() const
   {
         return typename R::Construct_circular_source_vertex_2()(*this);
   }
 
-  typename cpp11::result_of< typename R::Construct_circular_target_vertex_2(Line_arc_2)>::type
+  decltype(auto)
     target() const
   {
         return typename R::Construct_circular_target_vertex_2()(*this);
   }
 
-  typename cpp11::result_of< typename R::Construct_circular_min_vertex_2(Line_arc_2)>::type
+  decltype(auto)
   left() const
   {
         return typename R::Construct_circular_min_vertex_2()(*this);
   }
 
-  typename cpp11::result_of< typename R::Construct_circular_max_vertex_2(Line_arc_2)>::type
+  decltype(auto)
   right() const
   {
         return typename R::Construct_circular_max_vertex_2()(*this);