as_json works on child object

Gemfile

@@ -8,3 +8,7 @@ group :test do
   gem 'spork'
   gem 'autotest'
 end
+
+group :development do
+  gem 'pry'
+end

lib/serializable_decorator.rb

@@ -44,7 +44,17 @@ def instance_variable_get(name)
     __getobj__.instance_variable_get(name) || super
   end
 
+  def as_json
+    if __getobj__.respond_to?(:as_json) then
+      delegator_instance_vars = Delegator.instance_method(:instance_variables).bind(self).call
+      json_hash = Hash[delegator_instance_vars.map { | name | [name.to_s[1..-1], instance_variable_get(name) ] } ]
+      json_hash.merge!(__getobj__.as_json)
+    else
+      instance_values
+    end
+  end
+
   def to_json
-    instance_values.to_json
+    as_json.to_json
   end
 end

lib/serializable_decorator/version.rb

@@ -1,5 +1,5 @@
 module Delegators
   module SerializableDecorator
-    VERSION = "0.0.2"
+    VERSION = "0.0.3"
   end
 end

spec/serializable_decorator_spec.rb

@@ -4,13 +4,21 @@ class Test
   attr_accessor :foo
 end
 
+class TestJson < Test
+  attr_accessor :quux
+  def as_json
+    { extra: "baz", foo: @foo }
+  end
+end
+
 class TestDecorator < SerializableDecorator
   attr_accessor :bar
 end
 
 describe SerializableDecorator do
   before(:each) do
     @td = TestDecorator.new(Test.new)
+    @tdj = TestDecorator.new(TestJson.new)
   end
 
   it "Original attributes are still available" do
@@ -75,4 +83,12 @@ class TestDecorator < SerializableDecorator
   it "Should not include any extraneous entries in the JSON output" do
     @td.to_json.should == "{}"
   end
+
+  it "Should use the decorated object's as_json if it exists" do
+    @tdj.foo = 12
+    @tdj.bar = 13
+    @tdj.to_json.should include('"foo":12')
+    @tdj.to_json.should include('"bar":13')
+    @tdj.to_json.should include('"extra":"baz"')
+  end
 end