From 88c79dc23713ac9525562e66a938de479f10d328 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mael=20Rouxel-Labb=C3=A9?=
 <mael.rouxel.labbe@geometryfactory.com>
Date: Mon, 9 Jan 2023 11:06:54 +0100
Subject: [PATCH] Remove pointless template from Zero_gradient

---
 .../Implicit_cartesian_grid_domain.h          |  2 +-
 .../Isosurfacing_3/Implicit_octree_domain.h   |  2 +-
 .../CGAL/Isosurfacing_3/Zero_gradient.h       | 25 ++++++-------------
 3 files changed, 9 insertions(+), 20 deletions(-)

diff --git a/Isosurfacing_3/include/CGAL/Isosurfacing_3/Implicit_cartesian_grid_domain.h b/Isosurfacing_3/include/CGAL/Isosurfacing_3/Implicit_cartesian_grid_domain.h
index c10c45a3bd2..ff06eccf050 100644
--- a/Isosurfacing_3/include/CGAL/Isosurfacing_3/Implicit_cartesian_grid_domain.h
+++ b/Isosurfacing_3/include/CGAL/Isosurfacing_3/Implicit_cartesian_grid_domain.h
@@ -74,7 +74,7 @@ using Implicit_cartesian_grid_domain =
  */
 template <typename GeomTraits,
           typename PointFunction,
-          typename Gradient_ = Zero_gradient<GeomTraits> >
+          typename Gradient_ = Zero_gradient>
 Implicit_cartesian_grid_domain<GeomTraits, PointFunction, Gradient_>
 create_implicit_cartesian_grid_domain(const Bbox_3& bbox,
                                       const typename GeomTraits::Vector_3& spacing,
diff --git a/Isosurfacing_3/include/CGAL/Isosurfacing_3/Implicit_octree_domain.h b/Isosurfacing_3/include/CGAL/Isosurfacing_3/Implicit_octree_domain.h
index 9412587006c..1dc9d8efe43 100644
--- a/Isosurfacing_3/include/CGAL/Isosurfacing_3/Implicit_octree_domain.h
+++ b/Isosurfacing_3/include/CGAL/Isosurfacing_3/Implicit_octree_domain.h
@@ -71,7 +71,7 @@ using Implicit_octree_domain =
  */
 template <typename GeomTraits,
           typename PointFunction,
-          typename Gradient_ = Zero_gradient<GeomTraits> >
+          typename Gradient_ = Zero_gradient>
 Implicit_octree_domain<GeomTraits, PointFunction, Gradient_>
 create_implicit_octree_domain(const std::shared_ptr<internal::Octree_wrapper<GeomTraits> > octree,
                               const PointFunction& point_function,
diff --git a/Isosurfacing_3/include/CGAL/Isosurfacing_3/Zero_gradient.h b/Isosurfacing_3/include/CGAL/Isosurfacing_3/Zero_gradient.h
index 3d4a7d57c65..10a3b3e82b8 100644
--- a/Isosurfacing_3/include/CGAL/Isosurfacing_3/Zero_gradient.h
+++ b/Isosurfacing_3/include/CGAL/Isosurfacing_3/Zero_gradient.h
@@ -14,6 +14,8 @@
 
 #include <CGAL/license/Isosurfacing_3.h>
 
+#include <CGAL/Origin.h>
+
 namespace CGAL {
 namespace Isosurfacing {
 
@@ -23,32 +25,19 @@ namespace Isosurfacing {
  * \brief Class template for a gradient that is always zero.
  *
  * \details This gradient function can be used for Marching Cubes, which does not require a gradient.
- *
- * \tparam GeomTraits the traits for this gradient.
  */
-template <typename GeomTraits>
-class Zero_gradient
+struct Zero_gradient
 {
-public:
-  using Geom_traits = GeomTraits;
-  using Point = typename Geom_traits::Point_3;
-  using Vector = typename Geom_traits::Vector_3;
-
-public:
   /**
    * \ingroup PkgIsosurfacing3Ref
    *
-   * \brief Evaluate the gradient at a point in space.
-   *
-   * \param point the point at which the gradient is computed
+   * \return the null vector
    */
-  Vector operator()(const Point& point) const
+  template <typename P>
+  Null_vector operator()(const P&) const
   {
-    return zero;
+    return NULL_VECTOR;
   }
-
-private:
-  const Vector zero = Vector(0, 0, 0);
 };
 
 } // namespace Isosurfacing