rename empty_featureset => invalid_featureset to avoid ambiguity + add helper is_valid method

include/mapnik/featureset.hpp

@@ -41,21 +41,25 @@ struct MAPNIK_DECL Featureset : private util::noncopyable
     virtual ~Featureset() {}
 };
 
-
+struct MAPNIK_DECL invalid_featureset final : Featureset
-struct MAPNIK_DECL empty_featureset final : Featureset
 {
     feature_ptr next()
     {
         return feature_ptr();
     }
-    ~empty_featureset() {}
+    ~invalid_featureset() {}
 };
 
 using featureset_ptr = std::shared_ptr<Featureset>;
 
-inline featureset_ptr make_empty_featureset()
+inline featureset_ptr make_invalid_featureset()
 {
-    return std::make_shared<empty_featureset>();
+    return std::make_shared<invalid_featureset>();
+}
+
+inline bool is_valid(featureset_ptr const& ptr)
+{
+    return (dynamic_cast<invalid_featureset*>(ptr.get()) == nullptr) ? false : true;
 }
 
 }

plugins/input/csv/csv_datasource.cpp

@@ -431,7 +431,7 @@ mapnik::featureset_ptr csv_datasource::features(mapnik::query const& q) const
             return std::make_shared<csv_index_featureset>(filename_, filter, locator_, separator_, quote_, headers_, ctx_);
         }
     }
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 mapnik::featureset_ptr csv_datasource::features_at_point(mapnik::coord2d const& pt, double tol) const

plugins/input/geojson/geojson_datasource.cpp

@@ -588,7 +588,7 @@ mapnik::featureset_ptr geojson_datasource::features(mapnik::query const& q) cons
 
     }
     // otherwise return an empty featureset
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 mapnik::featureset_ptr geojson_datasource::features_at_point(mapnik::coord2d const& pt, double tol) const

plugins/input/ogr/ogr_datasource.cpp

@@ -560,7 +560,7 @@ featureset_ptr ogr_datasource::features(query const& q) const
         }
     }
 
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 featureset_ptr ogr_datasource::features_at_point(coord2d const& pt, double tol) const
@@ -603,5 +603,5 @@ featureset_ptr ogr_datasource::features_at_point(coord2d const& pt, double tol)
         }
     }
 
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }

plugins/input/pgraster/pgraster_datasource.cpp

@@ -998,7 +998,7 @@ featureset_ptr pgraster_datasource::features_with_context(query const& q,process
 
     }
 
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 
@@ -1011,7 +1011,7 @@ featureset_ptr pgraster_datasource::features_at_point(coord2d const& pt, double
     if (pool)
     {
         shared_ptr<Connection> conn = pool->borrowObject();
-        if (!conn) return mapnik::make_empty_featureset();
+        if (!conn) return mapnik::make_invalid_featureset();
 
         if (conn->isOK())
         {
@@ -1082,7 +1082,7 @@ featureset_ptr pgraster_datasource::features_at_point(coord2d const& pt, double
         }
     }
 
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 box2d<double> pgraster_datasource::envelope() const

plugins/input/postgis/postgis_datasource.cpp

@@ -942,7 +942,7 @@ featureset_ptr postgis_datasource::features_with_context(query const& q,processo
 
     }
 
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 
@@ -955,7 +955,7 @@ featureset_ptr postgis_datasource::features_at_point(coord2d const& pt, double t
     if (pool)
     {
         shared_ptr<Connection> conn = pool->borrowObject();
-        if (!conn) return mapnik::make_empty_featureset();
+        if (!conn) return mapnik::make_invalid_featureset();
 
         if (conn->isOK())
         {
@@ -1030,7 +1030,7 @@ featureset_ptr postgis_datasource::features_at_point(coord2d const& pt, double t
         }
     }
 
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 box2d<double> postgis_datasource::envelope() const

plugins/input/raster/raster_datasource.cpp

@@ -224,5 +224,5 @@ featureset_ptr raster_datasource::features_at_point(coord2d const&, double tol)
 {
     MAPNIK_LOG_WARN(raster) << "raster_datasource: feature_at_point not supported";
 
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }

plugins/input/sqlite/sqlite_datasource.cpp

@@ -551,7 +551,7 @@ featureset_ptr sqlite_datasource::features(query const& q) const
                                                      using_subquery_);
     }
 
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 featureset_ptr sqlite_datasource::features_at_point(coord2d const& pt, double tol) const
@@ -631,5 +631,5 @@ featureset_ptr sqlite_datasource::features_at_point(coord2d const& pt, double to
                                                      using_subquery_);
     }
 
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }

plugins/input/topojson/topojson_datasource.cpp

@@ -284,7 +284,7 @@ mapnik::featureset_ptr topojson_datasource::features(mapnik::query const& q) con
         }
     }
     // otherwise return an empty featureset pointer
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 mapnik::featureset_ptr topojson_datasource::features_at_point(mapnik::coord2d const& pt, double tol) const

src/map.cpp

@@ -746,7 +746,7 @@ featureset_ptr Map::query_point(unsigned index, double x, double y) const
         else s << " (map has no layers)";
         throw std::out_of_range(s.str());
     }
-    return mapnik::make_empty_featureset();
+    return mapnik::make_invalid_featureset();
 }
 
 featureset_ptr Map::query_map_point(unsigned index, double x, double y) const