Create DefaultSerializer so that as_json uses same interface.

This is to ensure that PORO's as_json is called if no serializer
is specified.

Original behaviour was that serializable_hash was being called,
overriding the as_json method.

active_model_serializers.gemspec

@@ -20,5 +20,6 @@ Gem::Specification.new do |gem|
   gem.add_dependency 'activemodel', '>= 3.0'
   gem.add_development_dependency "rails", ">= 3.0"
   gem.add_development_dependency "pry"
+  gem.add_development_dependency "pry-nav"
   gem.add_development_dependency "simplecov"
 end

lib/active_model/array_serializer.rb

@@ -1,6 +1,15 @@
 require "active_support/core_ext/class/attribute"
 
 module ActiveModel
+  class DefaultSerializer
+    attr_reader :object
+    def initialize(object)
+      @object = object
+    end
+    def serializable_hash
+      @object.as_json
+    end
+  end
   # Active Model Array Serializer
   #
   # It serializes an Array, checking if each element that implements
@@ -30,7 +39,7 @@ module ActiveModel
         if serializer
           serializer.new(item, @options)
         else
-          item
+          DefaultSerializer.new(item)
         end
       end
     end

test/array_serializer_test.rb

@@ -12,7 +12,7 @@ class ArraySerializerTest < ActiveModel::TestCase
     serializer = array.active_model_serializer.new(array, :scope => {:scope => true})
     assert_equal([
       { :model => "Model" },
-      { :last_name => "Valim", :ok => true, :first_name => "Jose", :scope => true },
+      { :first_name => "Jose", :last_name => "Valim", :ok => true, :scope => true },
       { :title => "Comment1" }
     ], serializer.as_json)
   end
@@ -51,5 +51,4 @@ class ArraySerializerTest < ActiveModel::TestCase
       { :title => "Post2" }
     ], serializer.as_json)
   end
-
 end

test/test_fakes.rb

@@ -68,7 +68,7 @@ class MyUserSerializer < ActiveModel::Serializer
   end
 end
 
-class CommentSerializer
+class CommentSerializer < ActiveModel::Serializer
   def initialize(comment, options={})
     @object = comment
   end