swap for Point_2 and Point_d

and make the implementations more similar, in case someone wants to
replace it with a macro at some point.

Cartesian_kernel/include/CGAL/Cartesian/Point_2.h

@@ -50,6 +50,15 @@ public:
   PointC2(const FT &hx, const FT &hy, const FT &hw)
     : base(hx, hy, hw) {}
 
+  friend void swap(Self& a, Self& b)
+#ifdef __cpp_lib_is_swappable
+    noexcept(std::is_nothrow_swappable_v<Vector_2_>)
+#endif
+  {
+    using std::swap;
+    swap(a.base, b.base);
+  }
+
   const FT& x() const
   {
       return base.x();

Cartesian_kernel/include/CGAL/Cartesian/Point_3.h

@@ -24,6 +24,7 @@ namespace CGAL {
 template < class R_ >
 class PointC3
 {
+  typedef PointC3<R_>                       Self;
   typedef typename R_::Vector_3             Vector_3;
   typedef typename R_::Point_3              Point_3;
   typedef typename R_::Aff_transformation_3 Aff_transformation_3;
@@ -47,7 +48,7 @@ public:
   PointC3(const FT &x, const FT &y, const FT &z, const FT &w)
     : base(x, y, z, w) {}
 
-  friend void swap(PointC3& a, PointC3& b)
+  friend void swap(Self& a, Self& b)
 #ifdef __cpp_lib_is_swappable
     noexcept(std::is_nothrow_swappable_v<Vector_3>)
 #endif

Cartesian_kernel/include/CGAL/Cartesian/Vector_2.h

@@ -27,6 +27,7 @@ namespace CGAL {
 template < class R_ >
 class VectorC2
 {
+  typedef VectorC2<R_>                      Self;
   typedef typename R_::FT                   FT;
   typedef typename R_::Point_2              Point_2;
   typedef typename R_::Vector_2             Vector_2;
@@ -55,6 +56,15 @@ public:
     : base( hw != FT(1) ? CGAL::make_array<FT>(hx/hw, hy/hw)
                         : CGAL::make_array(hx, hy) ) {}
 
+  friend void swap(Self& a, Self& b)
+#ifdef __cpp_lib_is_swappable
+    noexcept(std::is_nothrow_swappable_v<Base>)
+#endif
+  {
+    using std::swap;
+    swap(a.base, b.base);
+  }
+
   const FT & x() const
   {
       return CGAL::get_pointee_or_identity(base)[0];

Cartesian_kernel/include/CGAL/Cartesian/Vector_3.h

@@ -27,6 +27,7 @@ template < class R_ >
 class VectorC3
 {
 // https://doc.cgal.org/latest/Manual/devman_code_format.html#secprogramming_conventions
+  typedef VectorC3<R_>                      Self;
   typedef typename R_::FT                   FT_;
   typedef typename R_::Point_3              Point_3;
   typedef typename R_::Vector_3             Vector_3;
@@ -70,7 +71,7 @@ public:
     : base( w != FT_(1) ? CGAL::make_array<FT_>(x/w, y/w, z/w)
                        : CGAL::make_array(x, y, z) ) {}
 
-  friend void swap(VectorC3& a, VectorC3& b)
+  friend void swap(Self& a, Self& b)
 #ifdef __cpp_lib_is_swappable
     noexcept(std::is_nothrow_swappable_v<Base>)
 #endif

Kernel_23/include/CGAL/Point_2.h

@@ -48,12 +48,12 @@ public:
   typedef RPoint_2 Rep;
   typedef typename R_::Cartesian_const_iterator_2 Cartesian_const_iterator;
 
-  const Rep& rep() const
+  const Rep& rep() const noexcept
   {
     return *this;
   }
 
-  Rep& rep()
+  Rep& rep() noexcept
   {
     return *this;
   }
@@ -84,6 +84,15 @@ public:
     : RPoint_2(typename R::Construct_point_2()(Return_base_tag(), hx, hy, hw))
   {}
 
+  friend void swap(Self& a, Self& b)
+#ifdef __cpp_lib_is_swappable
+    noexcept(std::is_nothrow_swappable_v<Rep>)
+#endif
+  {
+    using std::swap;
+    swap(a.rep(), b.rep());
+  }
+
   typename cpp11::result_of<typename R::Compute_x_2(Point_2)>::type
   x() const
   {

Kernel_23/include/CGAL/Point_3.h

@@ -81,7 +81,7 @@ public:
     : Rep(typename R::Construct_point_3()(Return_base_tag(), hx, hy, hz, hw))
   {}
 
-  friend void swap(Point_3& a, Point_3& b)
+  friend void swap(Self& a, Self& b)
 #ifdef __cpp_lib_is_swappable
     noexcept(std::is_nothrow_swappable_v<Rep>)
 #endif

Kernel_23/include/CGAL/Vector_2.h

@@ -54,12 +54,12 @@ public:
   typedef RVector_2 Rep;
   typedef typename R_::Cartesian_const_iterator_2 Cartesian_const_iterator;
 
-  const Rep& rep() const
+  const Rep& rep() const noexcept
   {
     return *this;
   }
 
-  Rep& rep()
+  Rep& rep() noexcept
   {
     return *this;
   }
@@ -93,6 +93,15 @@ public:
   Vector_2(const RT &x, const RT &y, const RT &w)
       : RVector_2(typename R::Construct_vector_2()(Return_base_tag(), x,y,w)) {}
 
+  friend void swap(Self& a, Self& b)
+#ifdef __cpp_lib_is_swappable
+    noexcept(std::is_nothrow_swappable_v<Rep>)
+#endif
+  {
+    using std::swap;
+    swap(a.rep(), b.rep());
+  }
+
 
   typename cpp11::result_of<typename R::Compute_x_2(Vector_2)>::type
   x() const

Kernel_23/include/CGAL/Vector_3.h

@@ -93,7 +93,7 @@ public:
   Vector_3(const RT& x, const RT& y, const RT& z, const RT& w)
     : Rep(typename R::Construct_vector_3()(Return_base_tag(), x, y, z, w)) {}
 
-  friend void swap(Vector_3& a, Vector_3& b)
+  friend void swap(Self& a, Self& b)
 #ifdef __cpp_lib_is_swappable
     noexcept(std::is_nothrow_swappable_v<Rep>)
 #endif

NewKernel_d/include/CGAL/NewKernel_d/Wrapper/Point_d.h

@@ -51,12 +51,12 @@ public:
   typedef typename Get_type<Kbase, Point_tag>::type      Rep;
   //typedef typename CGAL::decay<typename boost::result_of<CPI(Rep,Begin_tag)>::type>::type Cartesian_const_iterator;
 
-  const Rep& rep() const
+  const Rep& rep() const noexcept
   {
     return *this;
   }
 
-  Rep& rep()
+  Rep& rep() noexcept
   {
     return *this;
   }
@@ -101,6 +101,14 @@ public:
   Point_d(Origin&& v)
     : Rep(CPBase()(std::move(v))) {}
 
+  friend void swap(Self& a, Self& b)
+#ifdef __cpp_lib_is_swappable
+    noexcept(std::is_nothrow_swappable_v<Rep>)
+#endif
+    {
+      using std::swap;
+      swap(a.rep(), b.rep());
+    }
 
   decltype(auto) cartesian(int i)const{
 	  return CCBase()(rep(),i);