adds #area method for all GeoJSON objects

README.md

@@ -23,7 +23,20 @@ Calculate the area inside of any [GeoJSON](https://github.com/geocrystal/geojson
 require "geojson_area"
 ```
 
-`GeoJSON::Area.area()` accept any `GeoJSON` object, and returns contained area as square meters.
+This adds `area` method for all `GeoJSON` objects:
+
+```crystal
+polygon = GeoJSON::Polygon.new([
+  [[-10.0, -10.0], [10.0, -10.0], [10.0, 10.0], [-10.0,-10.0]],
+  [[-1.0, -2.0], [3.0, -2.0], [3.0, 2.0], [-1.0,-2.0]]
+])
+
+polygon.area
+# => 2366726096087.807
+```
+
+Also you can use `GeoJSON::Area.area()` directly.
+This method accept any `GeoJSON` object, and returns contained area as square meters.
 
 ```crystal
 polygon = GeoJSON::Polygon.new([

spec/geojson_area_spec.cr

@@ -58,4 +58,15 @@ describe GeoJSON::Area do
     area = GeoJSON::Area.area(polygon)
     area.should eq(2366726096087.807)
   end
+
+  describe GeoJSON::Object do
+    it "#area" do
+      polygon = GeoJSON::Polygon.new([
+        [[-10.0, -10.0], [10.0, -10.0], [10.0, 10.0], [-10.0, -10.0]],
+        [[-1.0, -2.0], [3.0, -2.0], [3.0, 2.0], [-1.0, -2.0]],
+      ])
+
+      polygon.area.should eq(2366726096087.807)
+    end
+  end
 end

src/geojson/object.cr

@@ -0,0 +1,7 @@
+module GeoJSON
+  class Object
+    def area : Float64
+      GeoJSON::Area.area(self)
+    end
+  end
+end

src/geojson_area.cr

@@ -1,5 +1,6 @@
 require "geojson"
 require "./geojson/area"
+require "./geojson/object"
 
 module GeoJSON::Area
   VERSION = {{ `shards version #{__DIR__}`.chomp.stringify }}