- If a controller is in a namespace, serializer will be looked up in this namespace first.

- Serializers for associations will be looked up in a parent serializer's namespace first too.
- "Prefix" option for different versions of associations serializers. Example: has_many :users, as: :short -> ShortUserSerializer

TODO: tests, config option for enabling namespace lookup

lib/active_model/array_serializer.rb

@@ -21,6 +21,7 @@ module ActiveModel
       @resource_name   = options[:resource_name]
       @only            = options[:only] ? Array(options[:only]) : nil
       @except          = options[:except] ? Array(options[:except]) : nil
+      @namespace       = options[:namespace]
       @key_format      = options[:key_format] || options[:each_serializer].try(:key_format)
     end
     attr_accessor :object, :scope, :root, :meta_key, :meta, :key_format
@@ -32,7 +33,7 @@ module ActiveModel
     end
 
     def serializer_for(item)
-      serializer_class = @each_serializer || Serializer.serializer_for(item) || DefaultSerializer
+      serializer_class = @each_serializer || Serializer.serializer_for(item, namespace: @namespace) || DefaultSerializer
       serializer_class.new(item, scope: scope, key_format: key_format, only: @only, except: @except)
     end
 
@@ -58,6 +59,7 @@ module ActiveModel
     end
 
     private
+
     def instrumentation_keys
       [:object, :scope, :root, :meta_key, :meta, :each_serializer, :resource_name, :key_format]
     end