[strategies][comparable distance (result)] implement comparable distance

result variant support as in all other algorithms

include/boost/geometry/strategies/comparable_distance_result.hpp

@@ -10,10 +10,20 @@
 #ifndef BOOST_GEOMETRY_STRATEGIES_COMPARABLE_DISTANCE_RESULT_HPP
 #define BOOST_GEOMETRY_STRATEGIES_COMPARABLE_DISTANCE_RESULT_HPP
 
-#include <boost/geometry/strategies/default_comparable_strategy.hpp>
+#include <boost/mpl/always.hpp>
+#include <boost/mpl/bool.hpp>
+#include <boost/mpl/vector.hpp>
+
+#include <boost/variant/variant_fwd.hpp>
+
+#include <boost/geometry/core/point_type.hpp>
+
 #include <boost/geometry/strategies/default_strategy.hpp>
 #include <boost/geometry/strategies/distance.hpp>
-#include <boost/geometry/strategies/distance_result.hpp>
+
+#include <boost/geometry/util/compress_variant.hpp>
+#include <boost/geometry/util/transform_variant.hpp>
+#include <boost/geometry/util/combine_if.hpp>
 
 #include <boost/geometry/algorithms/detail/distance/default_strategies.hpp>
 
@@ -21,6 +31,141 @@
 namespace boost { namespace geometry
 {
 
+namespace resolve_strategy
+{
+
+template <typename Geometry1, typename Geometry2, typename Strategy>
+struct comparable_distance_result
+    : strategy::distance::services::return_type
+        <
+            typename strategy::distance::services::comparable_type
+                <
+                    Strategy
+                >::type,
+            typename point_type<Geometry1>::type,
+            typename point_type<Geometry2>::type
+        >
+{};
+
+template <typename Geometry1, typename Geometry2>
+struct comparable_distance_result<Geometry1, Geometry2, default_strategy>
+    : comparable_distance_result
+        <
+            Geometry1,
+            Geometry2,
+            typename detail::distance::default_strategy
+                <
+                    Geometry1, Geometry2
+                >::type
+        >
+{};
+
+} // namespace resolve_strategy
+
+
+namespace resolve_variant
+{
+
+template <typename Geometry1, typename Geometry2, typename Strategy>
+struct comparable_distance_result
+    : resolve_strategy::comparable_distance_result
+        <
+            Geometry1,
+            Geometry2,
+            Strategy
+        >
+{};
+
+
+template
+<
+    typename Geometry1,
+    BOOST_VARIANT_ENUM_PARAMS(typename T),
+    typename Strategy
+>
+struct comparable_distance_result
+    <
+        Geometry1, boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>, Strategy
+    >
+{
+    // A set of all variant type combinations that are compatible and
+    // implemented
+    typedef typename util::combine_if<
+        typename mpl::vector1<Geometry1>,
+        typename boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>::types,
+        mpl::always<mpl::true_>
+    >::type possible_input_types;
+
+    // The (possibly variant) result type resulting from these combinations
+    typedef typename compress_variant<
+        typename transform_variant<
+            possible_input_types,
+            resolve_strategy::comparable_distance_result<
+                mpl::first<mpl::_>,
+                mpl::second<mpl::_>,
+                Strategy
+            >,
+            mpl::back_inserter<mpl::vector0<> >
+        >::type
+    >::type type;
+};
+
+
+// Distance arguments are commutative
+template
+<
+    BOOST_VARIANT_ENUM_PARAMS(typename T),
+    typename Geometry2,
+    typename Strategy
+>
+struct comparable_distance_result
+    <
+        boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>,
+        Geometry2,
+        Strategy
+    > : public comparable_distance_result
+        <
+            Geometry2, boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>, Strategy
+        >
+{};
+
+
+template <BOOST_VARIANT_ENUM_PARAMS(typename T), typename Strategy>
+struct comparable_distance_result
+    <
+        boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>,
+        boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>,
+        Strategy
+    >
+{
+    // A set of all variant type combinations that are compatible and
+    // implemented
+    typedef typename util::combine_if
+        <
+            typename boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>::types,
+            typename boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>::types,
+            mpl::always<mpl::true_>
+        >::type possible_input_types;
+
+    // The (possibly variant) result type resulting from these combinations
+    typedef typename compress_variant<
+        typename transform_variant<
+            possible_input_types,
+            resolve_strategy::comparable_distance_result<
+                mpl::first<mpl::_>,
+                mpl::second<mpl::_>,
+                Strategy
+            >,
+            mpl::back_inserter<mpl::vector0<> >
+        >::type
+    >::type type;
+};
+
+} // namespace resolve_variant
+
+
+
+
 
 /*!
 \brief Meta-function defining return type of comparable_distance function
@@ -33,32 +178,15 @@ template
     typename Strategy = void
 >
 struct comparable_distance_result
-    : distance_result
+    : resolve_variant::comparable_distance_result
         <
-            Geometry1,
-            Geometry2,
-            typename strategy::distance::services::comparable_type
-                <
-                    Strategy
-                >::type
+            Geometry1, Geometry2, Strategy
         >
 {};
 
-template <typename Geometry1, typename Geometry2>
-struct comparable_distance_result<Geometry1, Geometry2, default_strategy>
-    : distance_result<Geometry1, Geometry2, default_comparable_strategy>
-{};
-
-template <typename Geometry1, typename Geometry2>
-struct comparable_distance_result
-    <
-        Geometry1, Geometry2, default_comparable_strategy
-    > : distance_result<Geometry1, Geometry2, default_comparable_strategy>
-{};
-
 template <typename Geometry1, typename Geometry2>
 struct comparable_distance_result<Geometry1, Geometry2, void>
-    : distance_result<Geometry1, Geometry2, default_comparable_strategy>
+    : comparable_distance_result<Geometry1, Geometry2, default_strategy>
 {};