use setup block to config which classes to extend

lib/validates_timeliness.rb

@@ -14,6 +14,10 @@ require 'active_support/core_ext/date_time/zones'
 
 module ValidatesTimeliness
 
+  # Add validation helpers to these classes
+  mattr_accessor :extend_classes
+  @@extend_classes = []
+
   # Set the dummy date part for a time type values.
   mattr_accessor :dummy_date_for_time_type
   @@dummy_date_for_time_type = [ 2000, 1, 1 ]
@@ -21,6 +25,12 @@ module ValidatesTimeliness
   # Ignore errors when restriction options are evaluated
   mattr_accessor :ignore_restriction_errors
   @@ignore_restriction_errors = false
+
+  # Setup method for plugin configuration
+  def self.setup
+    yield self
+    extend_classes.each {|klass| klass.send(:include, ValidatesTimeliness::HelperMethods) }
+  end
 end
 
 require 'validates_timeliness/conversion'

lib/validates_timeliness/helper_methods.rb

@@ -1,19 +1,19 @@
 module ValidatesTimeliness
   module HelperMethods
-    def validates_date(*attr_names)
-      validates_with Validator, _merge_attributes(attr_names).merge(:type => :date)
-    end
+    extend ActiveSupport::Concern
 
-    def validates_time(*attr_names)
-      validates_with Validator, _merge_attributes(attr_names).merge(:type => :time)
-    end
+    module ClassMethods
+      def validates_date(*attr_names)
+        validates_with Validator, _merge_attributes(attr_names).merge(:type => :date)
+      end
 
-    def validates_datetime(*attr_names)
-      validates_with Validator, _merge_attributes(attr_names).merge(:type => :datetime)
+      def validates_time(*attr_names)
+        validates_with Validator, _merge_attributes(attr_names).merge(:type => :time)
+      end
+
+      def validates_datetime(*attr_names)
+        validates_with Validator, _merge_attributes(attr_names).merge(:type => :datetime)
+      end
     end
   end
 end
-
-module ActiveModel::Validations::HelperMethods
-  include ValidatesTimeliness::HelperMethods
-end