geom/traits: add initial shape_traits trait

CMakeLists.txt

@@ -363,6 +363,7 @@ list (
     geom/segment.hpp
     geom/sphere.cpp
     geom/sphere.hpp
+    geom/traits.hpp
     geom/tri.cpp
     geom/tri.hpp
     hash.hpp

geom/traits.hpp

@@ -0,0 +1,30 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * Copyright 2019 Danny Robson <danny@nerdcruft.net>
+ */
+
+#pragma once
+
+#include "fwd.hpp"
+
+#include "../point.hpp"
+
+#include <cstddef>
+
+
+namespace cruft::geom {
+    template <typename ShapeT>
+    struct shape_traits { };
+
+
+    template <std::size_t S, typename T>
+    struct shape_traits <::cruft::region<S,T>> {
+        static constexpr auto elements = S;
+        using value_type = T;
+
+        using point_type = cruft::point<S,T>;
+    };
+}