Forces the order of valid roles upon sanitized roles in mask_for and sets the bitmaks default value to 0.

lib/role_model/class_methods.rb

@@ -19,15 +19,15 @@ module RoleModel
     end
 
     def mask_for(*roles)
-      (roles.map { |role|
+      sanitized_roles = roles.map { |role|
         role.respond_to?(:each) ? role.to_a : role
       }.flatten.map { |role|
         role.to_sym
-      } & valid_roles).map { |role|
-        2**valid_roles.index(role)
-      }.inject { |sum, bitvalue|
-        sum + bitvalue
-      } || 0
+      }
+
+      (valid_roles & sanitized_roles).inject(0) { |sum, role|
+        sum + 2**valid_roles.index(role)
+      }
     end
 
     protected