lib/physical/cuboid.rb in physical-0.4.3 vs lib/physical/cuboid.rb in physical-0.4.4

@@ -24,10 +24,11 @@
       return Measured::Density(0.0, :g_ml) if volume.value.infinite?
       Measured::Density(weight.convert_to(:g).value / volume.convert_to(:ml).value, :g_ml)
     end
 
     def ==(other)
-      id == other.id
+      other.is_a?(self.class) &&
+        id == other&.id
     end
 
     private
 
     NORMALIZED_METHOD_REGEX = /(\w+)\??$/