dynamically detect which model adapter to use given a class

lib/cancan/ability.rb

@@ -187,7 +187,8 @@ module CanCan
     end
 
     def model_adapter(model_class, action)
-      ModelAdapters::ActiveRecordAdapter.new(model_class, relevant_rules_for_query(action, model_class))
+      adapter_class = ModelAdapters::AbstractAdapter.adapter_class(model_class)
+      adapter_class.new(model_class, relevant_rules_for_query(action, model_class))
     end
 
     # See ControllerAdditions#authorize! for documentation.

lib/cancan/model_adapters/abstract_adapter.rb

@@ -1,6 +1,20 @@
 module CanCan
   module ModelAdapters
     class AbstractAdapter
+      def self.inherited(subclass)
+        @subclasses ||= []
+        @subclasses << subclass
+      end
+
+      def self.adapter_class(model_class)
+        @subclasses.detect { |subclass| subclass.for_class?(model_class) } || DefaultAdapter
+      end
+
+      # Used to determine if the given adapter should be used for the passed in class.
+      def self.for_class?(member_class)
+        false # override in subclass
+      end
+
       def initialize(model_class, rules)
         @model_class = model_class
         @rules = rules

lib/cancan/model_adapters/active_record_adapter.rb

@@ -1,6 +1,10 @@
 module CanCan
   module ModelAdapters
     class ActiveRecordAdapter < AbstractAdapter
+      def self.for_class?(model_class)
+        model_class <= ActiveRecord::Base
+      end
+
       # Returns conditions intended to be used inside a database query. Normally you will not call this
       # method directly, but instead go through ActiveRecordAdditions#accessible_by.
       #

lib/cancan/model_adapters/default_adapter.rb

@@ -0,0 +1,7 @@
+module CanCan
+  module ModelAdapters
+    class DefaultAdapter < AbstractAdapter
+      # This adapter is used when no matching adapter is found
+    end
+  end
+end