Refactor: introduce lazy association

lib/active_model/serializer/lazy_association.rb

@@ -0,0 +1,22 @@
+module ActiveModel
+  class Serializer
+    class LazyAssociation < Field
+
+      def serializer
+        options[:serializer]
+      end
+
+      def include_data?
+        options[:include_data]
+      end
+
+      def virtual_value
+        options[:virtual_value]
+      end
+
+      def reflection
+        options[:reflection]
+      end
+    end
+  end
+end