diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index aa9822c6ab6d4..ec85a20f70bbe 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -268,13 +268,13 @@ class Base < AbstractController::Base
 
     private_class_method :new #:nodoc:
 
-    extlib_inheritable_accessor :default_params
+    class_attribute :default_params
     self.default_params = {
       :mime_version => "1.0",
       :charset      => "utf-8",
       :content_type => "text/plain",
       :parts_order  => [ "text/plain", "text/enriched", "text/html" ]
-    }
+    }.freeze
 
     class << self
 
@@ -284,9 +284,9 @@ def mailer_name
       attr_writer :mailer_name
       alias :controller_path :mailer_name
 
-      def default(value=nil)
-        self.default_params.merge!(value) if value
-        self.default_params
+      def default(value = nil)
+        self.default_params = default_params.merge(value).freeze if value
+        default_params
       end
 
       # Receives a raw email, parses it into an email object, decodes it,
diff --git a/actionmailer/lib/action_mailer/delivery_methods.rb b/actionmailer/lib/action_mailer/delivery_methods.rb
index 7e92aea8fd0ce..043794bb12daf 100644
--- a/actionmailer/lib/action_mailer/delivery_methods.rb
+++ b/actionmailer/lib/action_mailer/delivery_methods.rb
@@ -7,8 +7,7 @@ module DeliveryMethods
     extend ActiveSupport::Concern
 
     included do
-      extlib_inheritable_accessor :delivery_methods, :delivery_method,
-                                  :instance_writer => false
+      class_attribute :delivery_methods, :delivery_method
 
       # Do not make this inheritable, because we always want it to propagate
       cattr_accessor :raise_delivery_errors
@@ -17,7 +16,7 @@ module DeliveryMethods
       cattr_accessor :perform_deliveries
       self.perform_deliveries = true
 
-      self.delivery_methods = {}
+      self.delivery_methods = {}.freeze
       self.delivery_method  = :smtp
 
       add_delivery_method :smtp, Mail::SMTP,
@@ -53,12 +52,9 @@ module ClassMethods
       #     :arguments  => '-i -t'
       # 
       def add_delivery_method(symbol, klass, default_options={})
-        unless respond_to?(:"#{symbol}_settings")
-          extlib_inheritable_accessor(:"#{symbol}_settings", :instance_writer => false)
-        end
-
+        class_attribute(:"#{symbol}_settings") unless respond_to?(:"#{symbol}_settings")
         send(:"#{symbol}_settings=", default_options)
-        self.delivery_methods[symbol.to_sym] = klass
+        self.delivery_methods = delivery_methods.merge(symbol.to_sym => klass).freeze
       end
 
       def wrap_delivery_behavior(mail, method=nil) #:nodoc:
@@ -87,4 +83,4 @@ def wrap_delivery_behavior!(*args) #:nodoc:
       self.class.wrap_delivery_behavior(message, *args)
     end
   end
-end
\ No newline at end of file
+end
diff --git a/actionmailer/lib/action_mailer/deprecated_api.rb b/actionmailer/lib/action_mailer/deprecated_api.rb
index 54ad18f796f44..c08ab4164e644 100644
--- a/actionmailer/lib/action_mailer/deprecated_api.rb
+++ b/actionmailer/lib/action_mailer/deprecated_api.rb
@@ -47,7 +47,7 @@ def template_root
       end
 
       def template_root=(root)
-        ActiveSupport::Deprecation.warn "template_root= is deprecated, use view_paths.unshift instead", caller[0,2]
+        ActiveSupport::Deprecation.warn "template_root= is deprecated, use prepend_view_path instead", caller[0,2]
         self.view_paths = ActionView::Base.process_view_paths(root)
       end
 
diff --git a/actionmailer/test/base_test.rb b/actionmailer/test/base_test.rb
index 57bfe2375e625..20ecfdcbdbe41 100644
--- a/actionmailer/test/base_test.rb
+++ b/actionmailer/test/base_test.rb
@@ -254,7 +254,7 @@ def different_layout(layout_name='')
   end
 
   test "subject gets default from I18n" do
-    BaseMailer.default[:subject] = nil
+    BaseMailer.default :subject => nil
     email = BaseMailer.welcome(:subject => nil)
     assert_equal "Welcome", email.subject
 
@@ -331,22 +331,24 @@ def different_layout(layout_name='')
   end
 
   test "implicit multipart with several view paths uses the first one with template" do
+    old = BaseMailer.view_paths
     begin
-      BaseMailer.view_paths.unshift(File.join(FIXTURE_LOAD_PATH, "another.path"))
+      BaseMailer.view_paths = [File.join(FIXTURE_LOAD_PATH, "another.path")] + old.dup
       email = BaseMailer.welcome
       assert_equal("Welcome from another path", email.body.encoded)
     ensure
-      BaseMailer.view_paths.shift
+      BaseMailer.view_paths = old
     end
   end
 
   test "implicit multipart with inexistent templates uses the next view path" do
+    old = BaseMailer.view_paths
     begin
-      BaseMailer.view_paths.unshift(File.join(FIXTURE_LOAD_PATH, "unknown"))
+      BaseMailer.view_paths = [File.join(FIXTURE_LOAD_PATH, "unknown")] + old.dup
       email = BaseMailer.welcome
       assert_equal("Welcome", email.body.encoded)
     ensure
-      BaseMailer.view_paths.shift
+      BaseMailer.view_paths = old
     end
   end
 
@@ -503,16 +505,10 @@ def swap(klass, new_values)
     end
 
     def with_default(klass, new_values)
-      hash = klass.default
-      old_values = {}
-      new_values.each do |key, value|
-        old_values[key] = hash[key]
-        hash[key] = value
-      end
+      old = klass.default_params
+      klass.default(new_values)
       yield
     ensure
-      old_values.each do |key, value|
-        hash[key] = value
-      end
+      klass.default_params = old
     end
 end
diff --git a/actionmailer/test/delivery_methods_test.rb b/actionmailer/test/delivery_methods_test.rb
index 4907ca09035ef..22a7d19bc25bf 100644
--- a/actionmailer/test/delivery_methods_test.rb
+++ b/actionmailer/test/delivery_methods_test.rb
@@ -45,7 +45,9 @@ def setup
 
   def teardown
     ActionMailer::Base.delivery_method = @old_delivery_method
-    ActionMailer::Base.delivery_methods.delete(:custom)
+    new = ActionMailer::Base.delivery_methods.dup
+    new.delete(:custom)
+    ActionMailer::Base.delivery_methods = new
   end
 
   test "allow to add custom delivery method" do
@@ -167,4 +169,4 @@ def teardown
     assert_equal(0, DeliveryMailer.deliveries.length)
   end
   
-end
\ No newline at end of file
+end
diff --git a/actionpack/lib/abstract_controller/helpers.rb b/actionpack/lib/abstract_controller/helpers.rb
index eb621c08651f3..578b884a4d535 100644
--- a/actionpack/lib/abstract_controller/helpers.rb
+++ b/actionpack/lib/abstract_controller/helpers.rb
@@ -1,4 +1,6 @@
 require 'active_support/dependencies'
+require 'active_support/core_ext/class/attribute'
+require 'active_support/core_ext/module/delegation'
 
 module AbstractController
   module Helpers
@@ -12,10 +14,10 @@ def self.next_serial
     end
 
     included do
-      extlib_inheritable_accessor(:_helpers) { Module.new }
-      extlib_inheritable_accessor(:_helper_serial) do
-        AbstractController::Helpers.next_serial
-      end
+      class_attribute :_helpers, :_helper_serial
+      delegate :_helpers, :to => :'self.class'
+      self._helpers = Module.new
+      self._helper_serial = ::AbstractController::Helpers.next_serial
     end
 
     module ClassMethods
diff --git a/actionpack/lib/abstract_controller/layouts.rb b/actionpack/lib/abstract_controller/layouts.rb
index 56ddf9bf01a19..0d214396aaf1f 100644
--- a/actionpack/lib/abstract_controller/layouts.rb
+++ b/actionpack/lib/abstract_controller/layouts.rb
@@ -1,3 +1,6 @@
+require 'active_support/core_ext/class/attribute'
+require 'active_support/core_ext/module/delegation'
+
 module AbstractController
   # Layouts reverse the common pattern of including shared headers and footers in many templates to isolate changes in
   # repeated setups. The inclusion pattern has pages that look like this:
@@ -161,8 +164,9 @@ module Layouts
     include Rendering
 
     included do
-      extlib_inheritable_accessor(:_layout_conditions) { Hash.new }
-      extlib_inheritable_accessor(:_action_has_layout) { Hash.new }
+      class_attribute :_layout_conditions
+      delegate :_layout_conditions, :to => :'self.class'
+      self._layout_conditions = {}
       _write_layout_method
     end
 
diff --git a/actionpack/lib/abstract_controller/rendering.rb b/actionpack/lib/abstract_controller/rendering.rb
index ac407bda5e845..619a49571bcdd 100644
--- a/actionpack/lib/abstract_controller/rendering.rb
+++ b/actionpack/lib/abstract_controller/rendering.rb
@@ -1,4 +1,7 @@
 require "abstract_controller/base"
+require 'active_support/core_ext/class/attribute'
+require 'active_support/core_ext/module/delegation'
+require 'active_support/core_ext/array/wrap'
 
 module AbstractController
   class DoubleRenderError < Error
@@ -13,8 +16,9 @@ module Rendering
     extend ActiveSupport::Concern
 
     included do
-      extlib_inheritable_accessor :_view_paths
-      self._view_paths ||= ActionView::PathSet.new
+      class_attribute :_view_paths
+      delegate :_view_paths, :to => :'self.class'
+      self._view_paths = ActionView::PathSet.new
     end
 
     # An instance of a view class. The default view class is ActionView::Base
@@ -156,7 +160,6 @@ def _determine_template(options)
       elsif options.key?(:file)
         options[:_template_name] = options[:file]
       end
-
       name = (options[:_template_name] || options[:action] || action_name).to_s
       options[:_prefix] ||= _prefix if (options.keys & [:partial, :file, :template]).empty?
 
@@ -201,7 +204,7 @@ def clear_template_caches!
       # the default view path. You may also provide a custom view path
       # (see ActionView::ViewPathSet for more information)
       def append_view_path(path)
-        self.view_paths << path
+        self.view_paths = view_paths.dup + Array.wrap(path)
       end
 
       # Prepend a path to the list of view paths for this controller.
@@ -212,12 +215,12 @@ def append_view_path(path)
       # (see ActionView::ViewPathSet for more information)
       def prepend_view_path(path)
         clear_template_caches!
-        self.view_paths.unshift(path)
+        self.view_paths = Array.wrap(path) + view_paths.dup
       end
 
       # A list of all of the default view paths for this controller.
       def view_paths
-        self._view_paths
+        _view_paths
       end
 
       # Set the view paths.
@@ -228,7 +231,8 @@ def view_paths
       def view_paths=(paths)
         clear_template_caches!
         self._view_paths = paths.is_a?(ActionView::PathSet) ? paths : ActionView::Base.process_view_paths(paths)
+        _view_paths.freeze
       end
     end
   end
-end
\ No newline at end of file
+end
diff --git a/actionpack/lib/action_controller/metal.rb b/actionpack/lib/action_controller/metal.rb
index 57627a6f0b8e9..2b35e111ec75f 100644
--- a/actionpack/lib/action_controller/metal.rb
+++ b/actionpack/lib/action_controller/metal.rb
@@ -1,4 +1,4 @@
-require 'active_support/core_ext/class/inheritable_attributes'
+require 'active_support/core_ext/class/attribute'
 
 module ActionController
   # ActionController::Metal provides a way to get a valid Rack application from a controller.
@@ -90,7 +90,12 @@ def call(env)
       end
     end
 
-    extlib_inheritable_accessor(:middleware_stack) { ActionDispatch::MiddlewareStack.new }
+    class_attribute :middleware_stack
+    self.middleware_stack = ActionDispatch::MiddlewareStack.new
+
+    def self.inherited(base)
+      self.middleware_stack = base.middleware_stack.dup
+    end
 
     def self.use(*args)
       middleware_stack.use(*args)
diff --git a/actionpack/lib/action_controller/metal/helpers.rb b/actionpack/lib/action_controller/metal/helpers.rb
index 05843a061b926..1b5a4c308016e 100644
--- a/actionpack/lib/action_controller/metal/helpers.rb
+++ b/actionpack/lib/action_controller/metal/helpers.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/class/attribute'
+
 module ActionController
   # The Rails framework provides a large number of helpers for working with +assets+, +dates+, +forms+,
   # +numbers+ and model objects, to name a few. These helpers are available to all templates
@@ -50,7 +52,7 @@ module Helpers
     include AbstractController::Helpers
 
     included do
-      extlib_inheritable_accessor(:helpers_path)
+      class_attribute :helpers_path
       self.helpers_path = []
     end
 
diff --git a/actionpack/lib/action_controller/metal/hide_actions.rb b/actionpack/lib/action_controller/metal/hide_actions.rb
index cdacdc40a606a..e893acffdf65c 100644
--- a/actionpack/lib/action_controller/metal/hide_actions.rb
+++ b/actionpack/lib/action_controller/metal/hide_actions.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/class/attribute'
+
 module ActionController
   # ActionController::HideActions adds the ability to prevent public methods on a controller
   # to be called as actions.
@@ -5,7 +7,8 @@ module HideActions
     extend ActiveSupport::Concern
 
     included do
-      extlib_inheritable_accessor(:hidden_actions) { Set.new }
+      class_attribute :hidden_actions
+      self.hidden_actions = Set.new
     end
 
   private
@@ -14,7 +17,7 @@ module HideActions
     # action name is in the list of hidden actions.
     def action_method?(action_name)
       self.class.visible_action?(action_name) do
-        !hidden_actions.include?(action_name) && super
+        !self.class.hidden_actions.include?(action_name) && super
       end
     end
 
@@ -24,7 +27,7 @@ module ClassMethods
       # ==== Parameters
       # *args<#to_s>:: A list of actions
       def hide_action(*args)
-        hidden_actions.merge(args.map! {|a| a.to_s })
+        self.hidden_actions = hidden_actions.dup.merge(args.map(&:to_s))
       end
 
       def inherited(klass)
diff --git a/actionpack/lib/action_controller/metal/mime_responds.rb b/actionpack/lib/action_controller/metal/mime_responds.rb
index 08599d660eb50..e70a20b2be7be 100644
--- a/actionpack/lib/action_controller/metal/mime_responds.rb
+++ b/actionpack/lib/action_controller/metal/mime_responds.rb
@@ -1,11 +1,12 @@
 require 'abstract_controller/collector'
+require 'active_support/core_ext/class/attribute'
 
 module ActionController #:nodoc:
   module MimeResponds #:nodoc:
     extend ActiveSupport::Concern
 
     included do
-      extlib_inheritable_accessor :responder, :mimes_for_respond_to, :instance_writer => false
+      class_attribute :responder, :mimes_for_respond_to
       self.responder = ActionController::Responder
       clear_respond_to
     end
@@ -38,18 +39,20 @@ def respond_to(*mimes)
         only_actions   = Array(options.delete(:only))
         except_actions = Array(options.delete(:except))
 
+        new = mimes_for_respond_to.dup
         mimes.each do |mime|
           mime = mime.to_sym
-          mimes_for_respond_to[mime]          = {}
-          mimes_for_respond_to[mime][:only]   = only_actions   unless only_actions.empty?
-          mimes_for_respond_to[mime][:except] = except_actions unless except_actions.empty?
+          new[mime]          = {}
+          new[mime][:only]   = only_actions   unless only_actions.empty?
+          new[mime][:except] = except_actions unless except_actions.empty?
         end
+        self.mimes_for_respond_to = new.freeze
       end
 
       # Clear all mimes in respond_to.
       #
       def clear_respond_to
-        self.mimes_for_respond_to = ActiveSupport::OrderedHash.new
+        self.mimes_for_respond_to = ActiveSupport::OrderedHash.new.freeze
       end
     end
 
@@ -218,12 +221,12 @@ def respond_to(*mimes, &block)
     #
     def respond_with(*resources, &block)
       raise "In order to use respond_with, first you need to declare the formats your " <<
-            "controller responds to in the class level" if mimes_for_respond_to.empty?
+            "controller responds to in the class level" if self.class.mimes_for_respond_to.empty?
 
       if response = retrieve_response_from_mimes(&block)
         options = resources.extract_options!
         options.merge!(:default_response => response)
-        (options.delete(:responder) || responder).call(self, resources, options)
+        (options.delete(:responder) || self.class.responder).call(self, resources, options)
       end
     end
 
@@ -235,8 +238,8 @@ def respond_with(*resources, &block)
     def collect_mimes_from_class_level #:nodoc:
       action = action_name.to_sym
 
-      mimes_for_respond_to.keys.select do |mime|
-        config = mimes_for_respond_to[mime]
+      self.class.mimes_for_respond_to.keys.select do |mime|
+        config = self.class.mimes_for_respond_to[mime]
 
         if config[:except]
           !config[:except].include?(action)
diff --git a/actionpack/lib/action_controller/metal/renderers.rb b/actionpack/lib/action_controller/metal/renderers.rb
index c1ba47927a837..639b508746769 100644
--- a/actionpack/lib/action_controller/metal/renderers.rb
+++ b/actionpack/lib/action_controller/metal/renderers.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/class/attribute'
+
 module ActionController
   def self.add_renderer(key, &block)
     Renderers.add(key, &block)
@@ -7,8 +9,8 @@ module Renderers
     extend ActiveSupport::Concern
 
     included do
-      extlib_inheritable_accessor :_renderers
-      self._renderers = {}
+      class_attribute :_renderers
+      self._renderers = {}.freeze
     end
 
     module ClassMethods
@@ -30,9 +32,11 @@ def _handle_render_options(options)
       end
 
       def use_renderers(*args)
+        new = _renderers.dup
         args.each do |key|
-          _renderers[key] = RENDERERS[key]
+          new[key] = RENDERERS[key]
         end
+        self._renderers = new.freeze
         _write_render_options
       end
       alias use_renderer use_renderers
diff --git a/actionpack/lib/action_controller/metal/request_forgery_protection.rb b/actionpack/lib/action_controller/metal/request_forgery_protection.rb
index f1fb4d7ce5396..276c70330738e 100644
--- a/actionpack/lib/action_controller/metal/request_forgery_protection.rb
+++ b/actionpack/lib/action_controller/metal/request_forgery_protection.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/class/attribute'
+
 module ActionController #:nodoc:
   class InvalidAuthenticityToken < ActionControllerError #:nodoc:
   end
@@ -13,7 +15,7 @@ module RequestForgeryProtection
       cattr_accessor :request_forgery_protection_token
 
       # Controls whether request forgergy protection is turned on or not. Turned off by default only in test mode.
-      extlib_inheritable_accessor :allow_forgery_protection
+      class_attribute :allow_forgery_protection
       self.allow_forgery_protection = true
 
       helper_method :form_authenticity_token
@@ -107,7 +109,7 @@ def form_authenticity_param
       end
 
       def protect_against_forgery?
-        allow_forgery_protection
+        self.class.allow_forgery_protection
       end
   end
 end
diff --git a/actionpack/lib/action_controller/metal/url_for.rb b/actionpack/lib/action_controller/metal/url_for.rb
index 387e6a554b9e7..51702368c1a23 100644
--- a/actionpack/lib/action_controller/metal/url_for.rb
+++ b/actionpack/lib/action_controller/metal/url_for.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/class/attribute'
+
 module ActionController
   # In <b>routes.rb</b> one defines URL-to-controller mappings, but the reverse
   # is also possible: an URL can be generated from one of your routing definitions.
@@ -85,9 +87,8 @@ module UrlFor
 
     included do
       ActionController::Routing::Routes.install_helpers(self)
-      extlib_inheritable_accessor :default_url_options,
-                                  :instance_writer => false, :instance_reader => false
-      self.default_url_options ||= {}
+      class_attribute :default_url_options
+      self.default_url_options = {}
     end
 
     # Overwrite to implement a number of default options that all url_for-based methods will use. The default options should come in
diff --git a/actionpack/lib/action_view/base.rb b/actionpack/lib/action_view/base.rb
index 148d507f1c9ec..4096c296c3576 100644
--- a/actionpack/lib/action_view/base.rb
+++ b/actionpack/lib/action_view/base.rb
@@ -1,5 +1,6 @@
 require 'active_support/core_ext/module/attr_internal'
 require 'active_support/core_ext/module/delegation'
+require 'active_support/core_ext/class/attribute'
 
 module ActionView #:nodoc:
   class ActionViewError < StandardError #:nodoc:
@@ -244,7 +245,7 @@ def self.process_view_paths(value)
       ActionView::PathSet.new(Array(value))
     end
 
-    extlib_inheritable_accessor :helpers
+    class_attribute :helpers
     attr_reader :helpers
 
     def self.for_controller(controller)
diff --git a/actionpack/lib/action_view/template/handler.rb b/actionpack/lib/action_view/template/handler.rb
index 221d1bd5c5677..8ecc9115194d0 100644
--- a/actionpack/lib/action_view/template/handler.rb
+++ b/actionpack/lib/action_view/template/handler.rb
@@ -1,5 +1,5 @@
-require "active_support/core_ext/class/inheritable_attributes"
 require "action_dispatch/http/mime_type"
+require 'active_support/core_ext/class/attribute'
 
 # Legacy TemplateHandler stub
 module ActionView
@@ -23,7 +23,7 @@ def compile(template)
     end
 
     class Template::Handler
-      extlib_inheritable_accessor :default_format
+      class_attribute :default_format
       self.default_format = Mime::HTML
 
       def self.call(template)
diff --git a/actionpack/lib/action_view/template/resolver.rb b/actionpack/lib/action_view/template/resolver.rb
index af5d6f6d181c9..6878067f7c92b 100644
--- a/actionpack/lib/action_view/template/resolver.rb
+++ b/actionpack/lib/action_view/template/resolver.rb
@@ -1,5 +1,6 @@
 require "pathname"
 require "active_support/core_ext/class"
+require "active_support/core_ext/array/wrap"
 require "action_view/template"
 
 module ActionView
@@ -11,7 +12,7 @@ class Resolver
 
     def self.register_detail(name, options = {})
       registered_details[name] = lambda do |val|
-        val ||= yield
+        val = Array.wrap(val || yield)
         val |= [nil] unless options[:allow_nil] == false
         val
       end
diff --git a/actionpack/test/controller/view_paths_test.rb b/actionpack/test/controller/view_paths_test.rb
index 05d2c8407c850..56821332c51fb 100644
--- a/actionpack/test/controller/view_paths_test.rb
+++ b/actionpack/test/controller/view_paths_test.rb
@@ -142,9 +142,9 @@ class C < ActionController::Base; end
     assert_paths A, "a/path"
     assert_paths A, *B.view_paths
     assert_paths C, *original_load_paths
-    
+
     C.view_paths = []
-    assert_nothing_raised { C.view_paths << 'c/path' }
+    assert_nothing_raised { C.append_view_path 'c/path' }
     assert_paths C, "c/path"
   end
 end
diff --git a/activerecord/lib/active_record/observer.rb b/activerecord/lib/active_record/observer.rb
index 4e05b819b52f0..0fbb1f0261dda 100644
--- a/activerecord/lib/active_record/observer.rb
+++ b/activerecord/lib/active_record/observer.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/class/attribute'
+
 module ActiveRecord
   # Observer classes respond to lifecycle callbacks to implement trigger-like
   # behavior outside the original class. This is a great way to reduce the
@@ -85,7 +87,8 @@ module ActiveRecord
   # singletons and that call instantiates and registers them.
   #
   class Observer < ActiveModel::Observer
-    extlib_inheritable_accessor(:observed_methods){ [] }
+    class_attribute :observed_methods
+    self.observed_methods = []
 
     def initialize
       super
@@ -93,7 +96,7 @@ def initialize
     end
 
     def self.method_added(method)
-      observed_methods << method if ActiveRecord::Callbacks::CALLBACKS.include?(method.to_sym)
+      self.observed_methods += [method] if ActiveRecord::Callbacks::CALLBACKS.include?(method.to_sym)
     end
 
     protected
@@ -106,7 +109,7 @@ def add_observer!(klass)
 
         # Check if a notifier callback was already added to the given class. If
         # it was not, add it.
-        self.observed_methods.each do |method|
+        self.class.observed_methods.each do |method|
           callback = :"_notify_observers_for_#{method}"
           if (klass.instance_methods & [callback, callback.to_s]).empty?
             klass.class_eval "def #{callback}; notify_observers(:#{method}); end"
diff --git a/activesupport/lib/active_support/rescuable.rb b/activesupport/lib/active_support/rescuable.rb
index 6e660f86478a3..e4c1651acf10b 100644
--- a/activesupport/lib/active_support/rescuable.rb
+++ b/activesupport/lib/active_support/rescuable.rb
@@ -1,4 +1,4 @@
-require 'active_support/core_ext/class/inheritable_attributes'
+require 'active_support/core_ext/class/attribute'
 require 'active_support/core_ext/proc'
 require 'active_support/core_ext/string/inflections'
 require 'active_support/core_ext/array/extract_options'
@@ -9,7 +9,7 @@ module Rescuable
     extend Concern
 
     included do
-      class_inheritable_accessor :rescue_handlers
+      class_attribute :rescue_handlers
       self.rescue_handlers = []
     end
 
@@ -67,7 +67,7 @@ def rescue_from(*klasses, &block)
           end
 
           # put the new handler at the end because the list is read in reverse
-          rescue_handlers << [key, options[:with]]
+          self.rescue_handlers += [[key, options[:with]]]
         end
       end
     end
@@ -83,7 +83,7 @@ def rescue_with_handler(exception)
     def handler_for_rescue(exception)
       # We go from right to left because pairs are pushed onto rescue_handlers
       # as rescue_from declarations are found.
-      _, rescuer = rescue_handlers.reverse.detect do |klass_name, handler|
+      _, rescuer = self.class.rescue_handlers.reverse.detect do |klass_name, handler|
         # The purpose of allowing strings in rescue_from is to support the
         # declaration of handler associations for exception classes whose
         # definition is yet unknown.
diff --git a/railties/lib/rails/generators/test_case.rb b/railties/lib/rails/generators/test_case.rb
index 38a3cbb0356f9..6b97c69d8d9c1 100644
--- a/railties/lib/rails/generators/test_case.rb
+++ b/railties/lib/rails/generators/test_case.rb
@@ -1,4 +1,5 @@
-require 'active_support/core_ext/class/inheritable_attributes'
+require 'active_support/core_ext/class/attribute'
+require 'active_support/core_ext/module/delegation'
 require 'active_support/core_ext/hash/reverse_merge'
 require 'rails/generators'
 require 'fileutils'
@@ -28,8 +29,8 @@ module Generators
     class TestCase < ActiveSupport::TestCase
       include FileUtils
 
-      extlib_inheritable_accessor :destination_root, :current_path, :generator_class,
-                                  :default_arguments, :instance_writer => false
+      class_attribute :destination_root, :current_path, :generator_class, :default_arguments
+      delegate :destination_root, :current_path, :generator_class, :default_arguments, :to => :'self.class'
 
       # Generators frequently change the current path using +FileUtils.cd+.
       # So we need to store the path at file load and revert back to it after each test.