Include Enumerable to ArraySerializer

lib/active_model/serializer/adapter/json_api_adapter.rb

@@ -8,9 +8,7 @@ module ActiveModel
           associations = serializer.associations(only: [:id]).each_with_object({}) do |(attr, value), h|
             h[attr] = case value
                        when ActiveModel::Serializer::ArraySerializer
-                         value.attributes(options).map do |item|
-                           item.id
-                         end.to_a
+                         value.map(&:id)
                        when ActiveModel::Serializer
                          # process belongs_to association
                        else

lib/active_model/serializer/array_serializer.rb

@@ -1,12 +1,11 @@
 module ActiveModel
   class Serializer
     class ArraySerializer < Serializer
-      def initialize(object)
-        @object = object
-      end
+      include Enumerable
+      delegate :each, to: :object
 
-      def attributes(options = {})
-        object.map do |item|
+      def initialize(object)
+        @object = object.map do |item|
           serializer_class = ActiveModel::Serializer.serializer_for(item)
           serializer_class.new(item)
         end