Add DynamicGeometry adaptation for std::variant.

include/boost/geometry/geometries/adapted/std_variant.hpp

@@ -0,0 +1,80 @@
+// Boost.Geometry
+
+// Copyright (c) 2021, Oracle and/or its affiliates.
+
+// Contributed and/or modified by Adam Wulkiewicz, on behalf of Oracle
+
+// Licensed under the Boost Software License version 1.0.
+// http://www.boost.org/users/license.html
+
+#ifndef BOOST_GEOMETRY_GEOMETRIES_ADAPTED_STD_VARIANT_HPP
+#define BOOST_GEOMETRY_GEOMETRIES_ADAPTED_STD_VARIANT_HPP
+
+
+#include <boost/config.hpp>
+
+#ifndef BOOST_NO_CXX17_HDR_VARIANT
+
+
+#include <utility>
+#include <variant>
+
+#include <boost/geometry/core/geometry_types.hpp>
+#include <boost/geometry/core/tag.hpp>
+#include <boost/geometry/core/tags.hpp>
+#include <boost/geometry/core/visit.hpp>
+#include <boost/geometry/util/sequence.hpp>
+
+
+namespace boost { namespace geometry
+{
+
+namespace traits
+{
+
+template <typename ...Ts>
+struct tag<std::variant<Ts...>>
+{
+    typedef dynamic_geometry_tag type;
+};
+
+template <typename ...Ts>
+struct visit<std::variant<Ts...>>
+{
+    template <typename Function, typename Variant>
+    static void apply(Function && function, Variant && variant)
+    {
+        std::visit(std::forward<Function>(function),
+                   std::forward<Variant>(variant));
+    }
+};
+
+template <typename ...Ts, typename ...Us>
+struct visit<std::variant<Ts...>, std::variant<Us...>>
+{
+    template <typename Function, typename Variant1, typename Variant2>
+    static void apply(Function && function, Variant1 && variant1, Variant2 && variant2)
+    {
+        std::visit(std::forward<Function>(function),
+                   std::forward<Variant1>(variant1),
+                   std::forward<Variant2>(variant2));
+    }
+};
+
+template <typename ...Ts>
+struct geometry_types<std::variant<Ts...>>
+{
+    typedef util::type_sequence<Ts...> type;
+};
+
+
+} // namespace traits
+
+
+}} // namespace boost::geometry
+
+
+#endif // BOOST_NO_CXX17_HDR_VARIANT
+
+
+#endif // BOOST_GEOMETRY_GEOMETRIES_ADAPTED_STD_VARIANT_HPP

test/algorithms/detail/visit.cpp

@@ -15,6 +15,7 @@
 #include <boost/geometry/geometries/adapted/boost_any.hpp>
 #include <boost/geometry/geometries/adapted/boost_variant.hpp>
 #include <boost/geometry/geometries/adapted/boost_variant2.hpp>
+#include <boost/geometry/geometries/adapted/std_variant.hpp>
 #include <boost/geometry/geometries/geometries.hpp>
 #include <boost/geometry/util/type_traits.hpp>
 
@@ -199,5 +200,9 @@ int test_main(int, char* [])
     test_all<boost::variant<point_t, linestring_t, polygon_t>>();
     test_all<boost::variant2::variant<point_t, linestring_t, polygon_t>>();
 
+#ifndef BOOST_NO_CXX17_HDR_VARIANT
+    test_all<std::variant<point_t, linestring_t, polygon_t>>();
+#endif
+
     return 0;
 }