Added arithmetic operator overrides to Point

Force them to return Point objects instead of Vectors

lib/geometry/point.rb

@@ -55,5 +55,20 @@ def y
 	def z
 	    @elements[2]
 	end
+
+# @group Arithmetic
+#  Override the arithmetic operators to force them to return {Point}s instead
+#  of {Vector}s
+
+	def +(other)
+	    Point[super]
+	end
+
+	def -(other)
+	    Point[super]
+	end
+
+# @endgroup
+
     end
 end

test/geometry/point.rb

@@ -1,9 +1,9 @@
 require_relative '../helper'
 require_relative '../../lib/geometry/point'
 
-class PointTest < Test::Unit::TestCase
-    Point = Geometry::Point
+Point = Geometry::Point
 
+class PointTest < Test::Unit::TestCase
     must "create a Point object using list syntax" do
 	point = Geometry::Point[2,1]
 	assert_equal(2, point.size)
@@ -86,3 +86,18 @@ class PointTest < Test::Unit::TestCase
 	assert_equal('Point[10, 11]', point.to_s)
     end
 end
+
+class PointArithmeticTest < Test::Unit::TestCase
+    def setup
+	@left = Point[1,2]
+	@right = Point[3,4]
+    end
+
+    must "return a Point when adding two Points" do
+	assert_kind_of(Point, @left+@right)
+    end
+
+    must "return a Point when subtracting two Points" do
+	assert_kind_of(Point, @left-@right)
+    end
+end