Refactoring: Assert readable by respond_to?

Belongs to #61

lib/unread/reader.rb

@@ -2,24 +2,13 @@ module Unread
   module Reader
     module ClassMethods
       def assert_readable(readable)
-        assert_readable_class
-
-        unless ReadMark.readable_classes.include?(readable.class) or is_single_table_inheritance?(readable.class)
-          raise ArgumentError, "Class #{readable.class.name} is not registered by acts_as_readable."
+        unless readable.respond_to?(:mark_as_read!)
+          raise ArgumentError, "Class #{readable.class} is not registered by acts_as_readable."
         end
-        raise ArgumentError, "The given #{readable.class.name} has no id." unless readable.id
-      end
 
-      def assert_readable_class
-        raise RuntimeError, 'There is no class using acts_as_readable.' unless ReadMark.readable_classes.try(:any?)
-      end
-
-      def is_single_table_inheritance?(readable)
-        readable.ancestors.each do |ancestor|
-          return true if ReadMark.readable_classes.include?(ancestor) and ancestor.table_name == readable.table_name
+        unless readable.id
+          raise ArgumentError, "The given #{readable.class} has no id."
         end
-
-        false
       end
     end