Move collection_radio to its own place.

lib/simple_form.rb

@@ -1,2 +1,5 @@
+require 'simple_form/builder_extensions'
 require 'simple_form/form_helper'
 require 'simple_form/form_builder'
+
+ActionView::Helpers::FormBuilder.send :include, SimpleForm::BuilderExtensions

lib/simple_form/builder_extensions.rb

@@ -0,0 +1,15 @@
+module SimpleForm
+  # A collection of methods required by simple_form but added to rails default form.
+  # This means that you can use such methods outside simple_form context.
+  module BuilderExtensions
+    def collection_radio(attribute, collection, value_method, text_method, html_options={})
+      collection.inject('') do |result, item|
+        value = item.send value_method
+        text  = item.send text_method
+
+        result << radio_button(attribute, value, html_options) <<
+                  label("#{attribute}_#{value}", text, :class => "radio")
+      end
+    end
+  end
+end

lib/simple_form/input.rb

@@ -53,15 +53,5 @@ module SimpleForm
         end
       end
 
-      def collection_radio(attribute, collection, value_method, text_method, html_options={})
-        collection.inject('') do |result, item|
-          value = item.send value_method
-          text  = item.send text_method
-
-          result << radio_button(attribute, value, html_options) <<
-                    label("#{attribute}_#{value}", text, :class => "radio")
-        end
-      end
-
   end
 end