we can define callbacks without a builder instance

activerecord/lib/active_record/associations/builder/association.rb

@@ -32,7 +32,7 @@ def self.build(model, name, scope, options, &block)
       builder = new(name, scope, options, &block)
       reflection = builder.build(model)
       builder.define_accessors model, reflection
-      builder.define_callbacks model, reflection
+      define_callbacks model, reflection
       builder.define_extensions model
       reflection
     end
@@ -68,8 +68,8 @@ def validate_options
     def define_extensions(model)
     end
 
-    def define_callbacks(model, reflection)
-      self.class.add_before_destroy_callbacks(model, reflection) if reflection.options[:dependent]
+    def self.define_callbacks(model, reflection)
+      add_before_destroy_callbacks(model, reflection) if reflection.options[:dependent]
       Association.extensions.each do |extension|
         extension.build model, reflection
       end

activerecord/lib/active_record/associations/builder/belongs_to.rb

@@ -12,10 +12,10 @@ def self.valid_dependent_options
       [:destroy, :delete]
     end
 
-    def define_callbacks(model, reflection)
+    def self.define_callbacks(model, reflection)
       super
-      self.class.add_counter_cache_callbacks(model, reflection) if reflection.options[:counter_cache]
-      self.class.add_touch_callbacks(model, reflection)         if reflection.options[:touch]
+      add_counter_cache_callbacks(model, reflection) if reflection.options[:counter_cache]
+      add_touch_callbacks(model, reflection)         if reflection.options[:touch]
     end
 
     def define_accessors(mixin, reflection)

activerecord/lib/active_record/associations/builder/collection_association.rb

@@ -23,12 +23,12 @@ def initialize(name, scope, options)
       end
     end
 
-    def define_callbacks(model, reflection)
+    def self.define_callbacks(model, reflection)
       super
       name    = reflection.name
       options = reflection.options
       CALLBACKS.each { |callback_name|
-        self.class.define_callback(model, callback_name, name, options)
+        define_callback(model, callback_name, name, options)
       }
     end
 

activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb

@@ -8,7 +8,7 @@ def valid_options
       super + [:join_table, :association_foreign_key]
     end
 
-    def define_callbacks(model, reflection)
+    def self.define_callbacks(model, reflection)
       super
       name = reflection.name
       model.send(:include, Module.new {