support different serializations in ArraySerializer

ArraySerializer can serialize arrays of Hash, ActiveModel::Serializer,
or any PORO that responds to :as_json

Each item in the array should not include its type as a root element,
since normal arrays do not do this. If you want "typed" collections,
don't use an Array.

lib/active_model/serializer.rb

@@ -52,7 +52,15 @@ module ActiveModel
       @options[:hash] = hash = {}
       @options[:unique_values] = {}
 
-      array = serializable_array.map(&:serializable_hash)
+      array = serializable_array.map do |item|
+        if item.is_a?(Hash)
+          item
+        elsif item.respond_to?(:serializable_hash)
+          item.serializable_hash
+        else
+          item.as_json
+        end
+      end
 
       if root = @options[:root]
         hash.merge!(root => array)

test/serializer_test.rb

@@ -375,17 +375,18 @@ class SerializerTest < ActiveModel::TestCase
     }, serializer.as_json)
   end
 
+  # serialize different typed objects
   def test_array_serializer
     model    = Model.new
     user     = User.new
     comments = Comment.new(:title => "Comment1", :id => 1)
 
     array = [model, user, comments]
-    serializer = array.active_model_serializer.new(array, {:scope => true})
+    serializer = array.active_model_serializer.new(array, :scope => {:scope => true})
     assert_equal([
       { :model => "Model" },
-      { :user => { :last_name=> "Valim", :ok => true, :first_name => "Jose", :scope => true } },
-      { :comment => { :title => "Comment1" } }
+      { :last_name => "Valim", :ok => true, :first_name => "Jose", :scope => true },
+      { :title => "Comment1" }
     ], serializer.as_json)
   end
 
@@ -403,6 +404,13 @@ class SerializerTest < ActiveModel::TestCase
     ]}, serializer.as_json)
   end
 
+  def test_array_serializer_with_hash
+    hash = {:value => "something"}
+    array = [hash]
+    serializer = array.active_model_serializer.new(array, :root => :items)
+    assert_equal({ :items => [ hash ]}, serializer.as_json)
+  end
+
   class CustomBlog < Blog
     attr_accessor :public_posts, :public_user
   end