diff --git a/actionmailer/lib/action_mailer.rb b/actionmailer/lib/action_mailer.rb
index 7f5bcad922776..43d73e71b9b62 100644
--- a/actionmailer/lib/action_mailer.rb
+++ b/actionmailer/lib/action_mailer.rb
@@ -34,6 +34,7 @@
 require 'active_support/core_ext/module/attr_internal'
 require 'active_support/core_ext/module/delegation'
 require 'active_support/core_ext/string/inflections'
+require 'active_support/lazy_load_hooks'
 
 module ActionMailer
   extend ::ActiveSupport::Autoload
diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index 48d6bbc8d9754..246816e9531c1 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -291,6 +291,8 @@ class Base < AbstractController::Base
       :parts_order  => [ "text/plain", "text/enriched", "text/html" ]
     }.freeze
 
+    ActionMailer.run_base_hooks(self)
+
     class << self
 
       def mailer_name
diff --git a/actionmailer/lib/action_mailer/railtie.rb b/actionmailer/lib/action_mailer/railtie.rb
index c5f18c7911c3a..0182e48425f64 100644
--- a/actionmailer/lib/action_mailer/railtie.rb
+++ b/actionmailer/lib/action_mailer/railtie.rb
@@ -6,19 +6,21 @@ class Railtie < Rails::Railtie
     railtie_name :action_mailer
 
     initializer "action_mailer.url_for", :before => :load_environment_config do |app|
-      ActionMailer::Base.send(:include, app.routes.url_helpers)
+      ActionMailer.base_hook { include app.routes.url_helpers }
     end
 
     require "action_mailer/railties/log_subscriber"
     log_subscriber ActionMailer::Railties::LogSubscriber.new
 
     initializer "action_mailer.logger" do
-      ActionMailer::Base.logger ||= Rails.logger
+      ActionMailer.base_hook { self.logger ||= Rails.logger }
     end
 
     initializer "action_mailer.set_configs" do |app|
-      app.config.action_mailer.each do |k,v|
-        ActionMailer::Base.send "#{k}=", v
+      ActionMailer.base_hook do
+        app.config.action_mailer.each do |k,v|
+          send "#{k}=", v
+        end
       end
     end
   end
diff --git a/actionpack/lib/action_controller/base.rb b/actionpack/lib/action_controller/base.rb
index 78871154c3438..d00afa6d4e9c4 100644
--- a/actionpack/lib/action_controller/base.rb
+++ b/actionpack/lib/action_controller/base.rb
@@ -58,6 +58,8 @@ def self.filter_parameter_logging(*args, &block)
       filter
     end
 
+    ActionController.run_base_hooks(self)
+
   end
 end
 
diff --git a/actionpack/lib/action_controller/railtie.rb b/actionpack/lib/action_controller/railtie.rb
index e9edf80451a88..ca03fc62da771 100644
--- a/actionpack/lib/action_controller/railtie.rb
+++ b/actionpack/lib/action_controller/railtie.rb
@@ -40,7 +40,7 @@ class Railtie < Rails::Railtie
     log_subscriber ActionController::Railties::LogSubscriber.new
 
     initializer "action_controller.logger" do
-      ActionController::Base.logger ||= Rails.logger
+      ActionController.base_hook { self.logger ||= Rails.logger }
     end
 
     initializer "action_controller.set_configs" do |app|
@@ -51,19 +51,23 @@ class Railtie < Rails::Railtie
       ac.stylesheets_dir = paths.public.stylesheets.to_a.first
       ac.secret = app.config.cookie_secret
 
-      ActionController::Base.config.replace(ac)
+      ActionController.base_hook { self.config.replace(ac) }
     end
 
     initializer "action_controller.initialize_framework_caches" do
-      ActionController::Base.cache_store ||= RAILS_CACHE
+      ActionController.base_hook { self.cache_store ||= RAILS_CACHE }
     end
 
     initializer "action_controller.set_helpers_path" do |app|
-      ActionController::Base.helpers_path = app.config.paths.app.helpers.to_a
+      ActionController.base_hook do
+        self.helpers_path = app.config.paths.app.helpers.to_a
+      end
     end
 
     initializer "action_controller.url_helpers" do |app|
-      ActionController::Base.extend ::ActionController::Railtie::UrlHelpers.with(app.routes)
+      ActionController.base_hook do
+        extend ::ActionController::Railtie::UrlHelpers.with(app.routes)
+      end
 
       message = "ActionController::Routing::Routes is deprecated. " \
                 "Instead, use Rails.application.routes"
diff --git a/actionpack/lib/action_dispatch/middleware/params_parser.rb b/actionpack/lib/action_dispatch/middleware/params_parser.rb
index 522982e2024f9..f4c4324fb0f38 100644
--- a/actionpack/lib/action_dispatch/middleware/params_parser.rb
+++ b/actionpack/lib/action_dispatch/middleware/params_parser.rb
@@ -1,4 +1,3 @@
-require 'active_support/json'
 require 'action_dispatch/http/request'
 
 module ActionDispatch
diff --git a/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb b/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
index db64711052c81..22da82479e3df 100644
--- a/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
+++ b/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
@@ -1,5 +1,4 @@
 require 'active_support/core_ext/hash/keys'
-require 'rack/request'
 
 module ActionDispatch
   module Session
diff --git a/actionpack/lib/action_dispatch/middleware/stack.rb b/actionpack/lib/action_dispatch/middleware/stack.rb
index 18a2922fa79e8..c52c8c0e6a6cd 100644
--- a/actionpack/lib/action_dispatch/middleware/stack.rb
+++ b/actionpack/lib/action_dispatch/middleware/stack.rb
@@ -58,7 +58,7 @@ def ==(middleware)
           if lazy_compare?(@klass) && lazy_compare?(middleware)
             normalize(@klass) == normalize(middleware)
           else
-            klass == ActiveSupport::Inflector.constantize(middleware.to_s)
+            klass.name == middleware.to_s
           end
         end
       end
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index 52e7b0e77df80..52a8df4273c95 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -1,3 +1,5 @@
+require "active_support/core_ext/hash/except"
+
 module ActionDispatch
   module Routing
     class Mapper
@@ -85,7 +87,7 @@ def conditions
           end
 
           def requirements
-            @requirements ||= returning(@options[:constraints] || {}) do |requirements|
+            @requirements ||= (@options[:constraints] || {}).tap do |requirements|
               requirements.reverse_merge!(@scope[:constraints]) if @scope[:constraints]
               @options.each { |k, v| requirements[k] = v if v.is_a?(Regexp) }
             end
diff --git a/actionpack/lib/action_view.rb b/actionpack/lib/action_view.rb
index f5035fe45a2ff..33bf0b8debede 100644
--- a/actionpack/lib/action_view.rb
+++ b/actionpack/lib/action_view.rb
@@ -41,6 +41,7 @@ module ActionView
       autoload :Rendering
     end
 
+    autoload :Base
     autoload :MissingTemplate,   'action_view/base'
     autoload :Resolver,          'action_view/template/resolver'
     autoload :PathResolver,      'action_view/template/resolver'
@@ -56,6 +57,5 @@ module ActionView
 end
 
 require 'active_support/core_ext/string/output_safety'
-require 'action_view/base'
 
 I18n.load_path << "#{File.dirname(__FILE__)}/action_view/locale/en.yml"
diff --git a/actionpack/lib/action_view/base.rb b/actionpack/lib/action_view/base.rb
index 76f9eb2b0d72d..e88ccc645e281 100644
--- a/actionpack/lib/action_view/base.rb
+++ b/actionpack/lib/action_view/base.rb
@@ -177,6 +177,8 @@ module Subclasses
 
     extend ActiveSupport::Memoizable
 
+    ActionView.run_base_hooks(self)
+
     attr_accessor :base_path, :assigns, :template_extension
     attr_internal :captures
 
diff --git a/actionpack/lib/action_view/helpers/active_model_helper.rb b/actionpack/lib/action_view/helpers/active_model_helper.rb
index ed83b8a8b2e22..4e12cdab5463e 100644
--- a/actionpack/lib/action_view/helpers/active_model_helper.rb
+++ b/actionpack/lib/action_view/helpers/active_model_helper.rb
@@ -5,9 +5,11 @@
 require 'active_support/core_ext/kernel/reporting'
 
 module ActionView
-  class Base
-    @@field_error_proc = Proc.new{ |html_tag, instance| "<div class=\"fieldWithErrors\">#{html_tag}</div>".html_safe }
-    cattr_accessor :field_error_proc
+  ActionView.base_hook do
+    class ActionView::Base
+      @@field_error_proc = Proc.new{ |html_tag, instance| "<div class=\"fieldWithErrors\">#{html_tag}</div>".html_safe }
+      cattr_accessor :field_error_proc
+    end
   end
 
   module Helpers
diff --git a/actionpack/lib/action_view/helpers/form_helper.rb b/actionpack/lib/action_view/helpers/form_helper.rb
index ace3bcfde37f2..742e873a4953e 100644
--- a/actionpack/lib/action_view/helpers/form_helper.rb
+++ b/actionpack/lib/action_view/helpers/form_helper.rb
@@ -1211,8 +1211,10 @@ def nested_child_index(name)
     end
   end
 
-  class Base
-    cattr_accessor :default_form_builder
-    @@default_form_builder = ::ActionView::Helpers::FormBuilder
+  ActionView.base_hook do
+    class ActionView::Base
+      cattr_accessor :default_form_builder
+      @@default_form_builder = ::ActionView::Helpers::FormBuilder
+    end
   end
 end
diff --git a/actionpack/lib/action_view/railtie.rb b/actionpack/lib/action_view/railtie.rb
index 03f18ac172294..2e5d115630317 100644
--- a/actionpack/lib/action_view/railtie.rb
+++ b/actionpack/lib/action_view/railtie.rb
@@ -10,7 +10,9 @@ class Railtie < Rails::Railtie
 
     initializer "action_view.cache_asset_timestamps" do |app|
       unless app.config.cache_classes
-        ActionView::Helpers::AssetTagHelper.cache_asset_timestamps = false
+        ActionView.base_hook do
+          ActionView::Helpers::AssetTagHelper.cache_asset_timestamps = false
+        end
       end
     end
   end
diff --git a/actionpack/lib/action_view/test_case.rb b/actionpack/lib/action_view/test_case.rb
index 72dbead14be08..1578ac94794f4 100644
--- a/actionpack/lib/action_view/test_case.rb
+++ b/actionpack/lib/action_view/test_case.rb
@@ -1,4 +1,5 @@
 require 'action_controller/test_case'
+require 'action_view'
 
 module ActionView
   class Base
diff --git a/actionpack/test/abstract_unit.rb b/actionpack/test/abstract_unit.rb
index d103c4e485243..67aa412d3d085 100644
--- a/actionpack/test/abstract_unit.rb
+++ b/actionpack/test/abstract_unit.rb
@@ -16,7 +16,6 @@
 require 'abstract_controller'
 require 'action_controller'
 require 'action_view'
-require 'action_view/base'
 require 'action_dispatch'
 require 'fixture_template'
 require 'active_support/dependencies'
diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index b79da4565d858..5942640c855d7 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -30,7 +30,6 @@
 
 require 'active_support'
 require 'active_model'
-require 'arel'
 
 module ActiveRecord
   extend ActiveSupport::Autoload
@@ -38,8 +37,8 @@ module ActiveRecord
   eager_autoload do
     autoload :VERSION
 
-    autoload :ActiveRecordError, 'active_record/base'
-    autoload :ConnectionNotEstablished, 'active_record/base'
+    autoload :ActiveRecordError, 'active_record/errors'
+    autoload :ConnectionNotEstablished, 'active_record/errors'
 
     autoload :Aggregations
     autoload :AssociationPreload
@@ -106,12 +105,16 @@ module ConnectionAdapters
 
     eager_autoload do
       autoload :AbstractAdapter
+      autoload :ConnectionManagement, "active_record/connection_adapters/abstract/connection_pool"
     end
   end
 
   autoload :TestCase
   autoload :TestFixtures, 'active_record/fixtures'
+
+  base_hook do
+    Arel::Table.engine = Arel::Sql::Engine.new(self)
+  end
 end
 
-Arel::Table.engine = Arel::Sql::Engine.new(ActiveRecord::Base)
-I18n.load_path << File.dirname(__FILE__) + '/active_record/locale/en.yml'
+I18n.load_path << File.dirname(__FILE__) + '/active_record/locale/en.yml'
\ No newline at end of file
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 042a67b490e26..52587ef251326 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -13,172 +13,10 @@
 require 'active_support/core_ext/string/behavior'
 require 'active_support/core_ext/object/singleton_class'
 require 'active_support/core_ext/module/delegation'
+require 'arel'
+require 'active_record/errors'
 
 module ActiveRecord #:nodoc:
-  # Generic Active Record exception class.
-  class ActiveRecordError < StandardError
-  end
-
-  # Raised when the single-table inheritance mechanism fails to locate the subclass
-  # (for example due to improper usage of column that +inheritance_column+ points to).
-  class SubclassNotFound < ActiveRecordError #:nodoc:
-  end
-
-  # Raised when an object assigned to an association has an incorrect type.
-  #
-  #   class Ticket < ActiveRecord::Base
-  #     has_many :patches
-  #   end
-  #
-  #   class Patch < ActiveRecord::Base
-  #     belongs_to :ticket
-  #   end
-  #
-  #   # Comments are not patches, this assignment raises AssociationTypeMismatch.
-  #   @ticket.patches << Comment.new(:content => "Please attach tests to your patch.")
-  class AssociationTypeMismatch < ActiveRecordError
-  end
-
-  # Raised when unserialized object's type mismatches one specified for serializable field.
-  class SerializationTypeMismatch < ActiveRecordError
-  end
-
-  # Raised when adapter not specified on connection (or configuration file <tt>config/database.yml</tt> misses adapter field).
-  class AdapterNotSpecified < ActiveRecordError
-  end
-
-  # Raised when Active Record cannot find database adapter specified in <tt>config/database.yml</tt> or programmatically.
-  class AdapterNotFound < ActiveRecordError
-  end
-
-  # Raised when connection to the database could not been established (for example when <tt>connection=</tt> is given a nil object).
-  class ConnectionNotEstablished < ActiveRecordError
-  end
-
-  # Raised when Active Record cannot find record by given id or set of ids.
-  class RecordNotFound < ActiveRecordError
-  end
-
-  # Raised by ActiveRecord::Base.save! and ActiveRecord::Base.create! methods when record cannot be
-  # saved because record is invalid.
-  class RecordNotSaved < ActiveRecordError
-  end
-
-  # Raised when SQL statement cannot be executed by the database (for example, it's often the case for MySQL when Ruby driver used is too old).
-  class StatementInvalid < ActiveRecordError
-  end
-
-  # Raised when SQL statement is invalid and the application gets a blank result.
-  class ThrowResult < ActiveRecordError
-  end
-
-  # Parent class for all specific exceptions which wrap database driver exceptions
-  # provides access to the original exception also.
-  class WrappedDatabaseException < StatementInvalid
-    attr_reader :original_exception
-
-    def initialize(message, original_exception)
-      super(message)
-      @original_exception = original_exception
-    end
-  end
-
-  # Raised when a record cannot be inserted because it would violate a uniqueness constraint.
-  class RecordNotUnique < WrappedDatabaseException
-  end
-
-  # Raised when a record cannot be inserted or updated because it references a non-existent record.
-  class InvalidForeignKey < WrappedDatabaseException
-  end
-
-  # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
-  # does not match number of expected variables.
-  #
-  # For example, in
-  #
-  #   Location.find :all, :conditions => ["lat = ? AND lng = ?", 53.7362]
-  #
-  # two placeholders are given but only one variable to fill them.
-  class PreparedStatementInvalid < ActiveRecordError
-  end
-
-  # Raised on attempt to save stale record. Record is stale when it's being saved in another query after
-  # instantiation, for example, when two users edit the same wiki page and one starts editing and saves
-  # the page before the other.
-  #
-  # Read more about optimistic locking in ActiveRecord::Locking module RDoc.
-  class StaleObjectError < ActiveRecordError
-  end
-
-  # Raised when association is being configured improperly or
-  # user tries to use offset and limit together with has_many or has_and_belongs_to_many associations.
-  class ConfigurationError < ActiveRecordError
-  end
-
-  # Raised on attempt to update record that is instantiated as read only.
-  class ReadOnlyRecord < ActiveRecordError
-  end
-
-  # ActiveRecord::Transactions::ClassMethods.transaction uses this exception
-  # to distinguish a deliberate rollback from other exceptional situations.
-  # Normally, raising an exception will cause the +transaction+ method to rollback
-  # the database transaction *and* pass on the exception. But if you raise an
-  # ActiveRecord::Rollback exception, then the database transaction will be rolled back,
-  # without passing on the exception.
-  #
-  # For example, you could do this in your controller to rollback a transaction:
-  #
-  #   class BooksController < ActionController::Base
-  #     def create
-  #       Book.transaction do
-  #         book = Book.new(params[:book])
-  #         book.save!
-  #         if today_is_friday?
-  #           # The system must fail on Friday so that our support department
-  #           # won't be out of job. We silently rollback this transaction
-  #           # without telling the user.
-  #           raise ActiveRecord::Rollback, "Call tech support!"
-  #         end
-  #       end
-  #       # ActiveRecord::Rollback is the only exception that won't be passed on
-  #       # by ActiveRecord::Base.transaction, so this line will still be reached
-  #       # even on Friday.
-  #       redirect_to root_url
-  #     end
-  #   end
-  class Rollback < ActiveRecordError
-  end
-
-  # Raised when attribute has a name reserved by Active Record (when attribute has name of one of Active Record instance methods).
-  class DangerousAttributeError < ActiveRecordError
-  end
-
-  # Raised when unknown attributes are supplied via mass assignment.
-  class UnknownAttributeError < NoMethodError
-  end
-
-  # Raised when an error occurred while doing a mass assignment to an attribute through the
-  # <tt>attributes=</tt> method. The exception has an +attribute+ property that is the name of the
-  # offending attribute.
-  class AttributeAssignmentError < ActiveRecordError
-    attr_reader :exception, :attribute
-    def initialize(message, exception, attribute)
-      @exception = exception
-      @attribute = attribute
-      @message = message
-    end
-  end
-
-  # Raised when there are multiple errors while doing a mass assignment through the +attributes+
-  # method. The exception has an +errors+ property that contains an array of AttributeAssignmentError
-  # objects, each corresponding to the error while assigning to an attribute.
-  class MultiparameterAssignmentErrors < ActiveRecordError
-    attr_reader :errors
-    def initialize(errors)
-      @errors = errors
-    end
-  end
-
   # Active Record objects don't specify their attributes directly, but rather infer them from the table definition with
   # which they're linked. Adding, removing, and changing attributes and their type is done directly in the database. Any change
   # is instantly reflected in the Active Record objects. The mapping that binds a given Active Record class to a certain
@@ -551,7 +389,7 @@ def self.reset_subclasses #:nodoc:
     class << self # Class methods
       def colorize_logging(*args)
         ActiveSupport::Deprecation.warn "ActiveRecord::Base.colorize_logging and " <<
-          "config.active_record.colorize_logging are deprecated. Please use " << 
+          "config.active_record.colorize_logging are deprecated. Please use " <<
           "Rails::LogSubscriber.colorize_logging or config.colorize_logging instead", caller
       end
       alias :colorize_logging= :colorize_logging
@@ -2401,8 +2239,10 @@ def object_from_yaml(string)
 
     include Aggregations, Transactions, Reflection, Serialization
 
+    NilClass.add_whiner(self) if NilClass.respond_to?(:add_whiner)
   end
 end
 
 # TODO: Remove this and make it work with LAZY flag
 require 'active_record/connection_adapters/abstract_adapter'
+ActiveRecord.run_base_hooks(ActiveRecord::Base)
\ No newline at end of file
diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
new file mode 100644
index 0000000000000..cf5ddca2ba981
--- /dev/null
+++ b/activerecord/lib/active_record/errors.rb
@@ -0,0 +1,165 @@
+module ActiveRecord
+  # Generic Active Record exception class.
+  class ActiveRecordError < StandardError
+  end
+
+  # Raised when the single-table inheritance mechanism fails to locate the subclass
+  # (for example due to improper usage of column that +inheritance_column+ points to).
+  class SubclassNotFound < ActiveRecordError #:nodoc:
+  end
+
+  # Raised when an object assigned to an association has an incorrect type.
+  #
+  #   class Ticket < ActiveRecord::Base
+  #     has_many :patches
+  #   end
+  #
+  #   class Patch < ActiveRecord::Base
+  #     belongs_to :ticket
+  #   end
+  #
+  #   # Comments are not patches, this assignment raises AssociationTypeMismatch.
+  #   @ticket.patches << Comment.new(:content => "Please attach tests to your patch.")
+  class AssociationTypeMismatch < ActiveRecordError
+  end
+
+  # Raised when unserialized object's type mismatches one specified for serializable field.
+  class SerializationTypeMismatch < ActiveRecordError
+  end
+
+  # Raised when adapter not specified on connection (or configuration file <tt>config/database.yml</tt> misses adapter field).
+  class AdapterNotSpecified < ActiveRecordError
+  end
+
+  # Raised when Active Record cannot find database adapter specified in <tt>config/database.yml</tt> or programmatically.
+  class AdapterNotFound < ActiveRecordError
+  end
+
+  # Raised when connection to the database could not been established (for example when <tt>connection=</tt> is given a nil object).
+  class ConnectionNotEstablished < ActiveRecordError
+  end
+
+  # Raised when Active Record cannot find record by given id or set of ids.
+  class RecordNotFound < ActiveRecordError
+  end
+
+  # Raised by ActiveRecord::Base.save! and ActiveRecord::Base.create! methods when record cannot be
+  # saved because record is invalid.
+  class RecordNotSaved < ActiveRecordError
+  end
+
+  # Raised when SQL statement cannot be executed by the database (for example, it's often the case for MySQL when Ruby driver used is too old).
+  class StatementInvalid < ActiveRecordError
+  end
+
+  # Raised when SQL statement is invalid and the application gets a blank result.
+  class ThrowResult < ActiveRecordError
+  end
+
+  # Parent class for all specific exceptions which wrap database driver exceptions
+  # provides access to the original exception also.
+  class WrappedDatabaseException < StatementInvalid
+    attr_reader :original_exception
+
+    def initialize(message, original_exception)
+      super(message)
+      @original_exception = original_exception
+    end
+  end
+
+  # Raised when a record cannot be inserted because it would violate a uniqueness constraint.
+  class RecordNotUnique < WrappedDatabaseException
+  end
+
+  # Raised when a record cannot be inserted or updated because it references a non-existent record.
+  class InvalidForeignKey < WrappedDatabaseException
+  end
+
+  # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
+  # does not match number of expected variables.
+  #
+  # For example, in
+  #
+  #   Location.find :all, :conditions => ["lat = ? AND lng = ?", 53.7362]
+  #
+  # two placeholders are given but only one variable to fill them.
+  class PreparedStatementInvalid < ActiveRecordError
+  end
+
+  # Raised on attempt to save stale record. Record is stale when it's being saved in another query after
+  # instantiation, for example, when two users edit the same wiki page and one starts editing and saves
+  # the page before the other.
+  #
+  # Read more about optimistic locking in ActiveRecord::Locking module RDoc.
+  class StaleObjectError < ActiveRecordError
+  end
+
+  # Raised when association is being configured improperly or
+  # user tries to use offset and limit together with has_many or has_and_belongs_to_many associations.
+  class ConfigurationError < ActiveRecordError
+  end
+
+  # Raised on attempt to update record that is instantiated as read only.
+  class ReadOnlyRecord < ActiveRecordError
+  end
+
+  # ActiveRecord::Transactions::ClassMethods.transaction uses this exception
+  # to distinguish a deliberate rollback from other exceptional situations.
+  # Normally, raising an exception will cause the +transaction+ method to rollback
+  # the database transaction *and* pass on the exception. But if you raise an
+  # ActiveRecord::Rollback exception, then the database transaction will be rolled back,
+  # without passing on the exception.
+  #
+  # For example, you could do this in your controller to rollback a transaction:
+  #
+  #   class BooksController < ActionController::Base
+  #     def create
+  #       Book.transaction do
+  #         book = Book.new(params[:book])
+  #         book.save!
+  #         if today_is_friday?
+  #           # The system must fail on Friday so that our support department
+  #           # won't be out of job. We silently rollback this transaction
+  #           # without telling the user.
+  #           raise ActiveRecord::Rollback, "Call tech support!"
+  #         end
+  #       end
+  #       # ActiveRecord::Rollback is the only exception that won't be passed on
+  #       # by ActiveRecord::Base.transaction, so this line will still be reached
+  #       # even on Friday.
+  #       redirect_to root_url
+  #     end
+  #   end
+  class Rollback < ActiveRecordError
+  end
+
+  # Raised when attribute has a name reserved by Active Record (when attribute has name of one of Active Record instance methods).
+  class DangerousAttributeError < ActiveRecordError
+  end
+
+  # Raised when unknown attributes are supplied via mass assignment.
+  class UnknownAttributeError < NoMethodError
+  end
+
+  # Raised when an error occurred while doing a mass assignment to an attribute through the
+  # <tt>attributes=</tt> method. The exception has an +attribute+ property that is the name of the
+  # offending attribute.
+  class AttributeAssignmentError < ActiveRecordError
+    attr_reader :exception, :attribute
+    def initialize(message, exception, attribute)
+      @exception = exception
+      @attribute = attribute
+      @message = message
+    end
+  end
+
+  # Raised when there are multiple errors while doing a mass assignment through the +attributes+
+  # method. The exception has an +errors+ property that contains an array of AttributeAssignmentError
+  # objects, each corresponding to the error while assigning to an attribute.
+  class MultiparameterAssignmentErrors < ActiveRecordError
+    attr_reader :errors
+    def initialize(errors)
+      @errors = errors
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index b38bd9a6445ae..60addd46c6220 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -24,31 +24,39 @@ class Railtie < Rails::Railtie
     log_subscriber ActiveRecord::Railties::LogSubscriber.new
 
     initializer "active_record.initialize_timezone" do
-      ActiveRecord::Base.time_zone_aware_attributes = true
-      ActiveRecord::Base.default_timezone = :utc
+      ActiveRecord.base_hook do
+        self.time_zone_aware_attributes = true
+        self.default_timezone = :utc
+      end
     end
 
     initializer "active_record.logger" do
-      ActiveRecord::Base.logger ||= ::Rails.logger
+      ActiveRecord.base_hook { self.logger ||= ::Rails.logger }
     end
 
     initializer "active_record.set_configs" do |app|
-      app.config.active_record.each do |k,v|
-        ActiveRecord::Base.send "#{k}=", v
+      ActiveRecord.base_hook do
+        app.config.active_record.each do |k,v|
+          send "#{k}=", v
+        end
       end
     end
 
     # This sets the database configuration from Configuration#database_configuration
     # and then establishes the connection.
     initializer "active_record.initialize_database" do |app|
-      ActiveRecord::Base.configurations = app.config.database_configuration
-      ActiveRecord::Base.establish_connection
+      ActiveRecord.base_hook do
+        self.configurations = app.config.database_configuration
+        establish_connection
+      end
     end
 
     # Expose database runtime to controller for logging.
     initializer "active_record.log_runtime" do |app|
       require "active_record/railties/controller_runtime"
-      ActionController::Base.send :include, ActiveRecord::Railties::ControllerRuntime
+      ActionController.base_hook do
+        include ActiveRecord::Railties::ControllerRuntime
+      end
     end
 
     # Setup database middleware after initializers have run
@@ -64,18 +72,22 @@ class Railtie < Rails::Railtie
     end
 
     initializer "active_record.load_observers" do
-      ActiveRecord::Base.instantiate_observers
+      ActiveRecord.base_hook { instantiate_observers }
 
-      ActionDispatch::Callbacks.to_prepare(:activerecord_instantiate_observers) do
-        ActiveRecord::Base.instantiate_observers
+      ActiveRecord.base_hook do
+        ActionDispatch::Callbacks.to_prepare(:activerecord_instantiate_observers) do
+          ActiveRecord::Base.instantiate_observers
+        end
       end
     end
 
     initializer "active_record.set_dispatch_hooks", :before => :set_clear_dependencies_hook do |app|
-      unless app.config.cache_classes
-        ActionDispatch::Callbacks.after do
-          ActiveRecord::Base.reset_subclasses
-          ActiveRecord::Base.clear_reloadable_connections!
+      ActiveRecord.base_hook do
+        unless app.config.cache_classes
+          ActionDispatch::Callbacks.after do
+            ActiveRecord::Base.reset_subclasses
+            ActiveRecord::Base.clear_reloadable_connections!
+          end
         end
       end
     end
diff --git a/activerecord/test/cases/helper.rb b/activerecord/test/cases/helper.rb
index f77dc801dcf30..e831ebf36c489 100644
--- a/activerecord/test/cases/helper.rb
+++ b/activerecord/test/cases/helper.rb
@@ -9,6 +9,7 @@
 require 'stringio'
 
 require 'active_record'
+require 'active_support/dependencies'
 require 'connection'
 
 begin
diff --git a/activesupport/lib/active_support.rb b/activesupport/lib/active_support.rb
index ae31d191c0874..e34e46b4cfd04 100644
--- a/activesupport/lib/active_support.rb
+++ b/activesupport/lib/active_support.rb
@@ -53,6 +53,7 @@ module ActiveSupport
     autoload :Deprecation
     autoload :Gzip
     autoload :Inflector
+    autoload :JSON
     autoload :Memoizable
     autoload :MessageEncryptor
     autoload :MessageVerifier
@@ -70,3 +71,5 @@ module ActiveSupport
   autoload :SafeBuffer, "active_support/core_ext/string/output_safety"
   autoload :TestCase
 end
+
+autoload :I18n, "active_support/i18n"
diff --git a/activesupport/lib/active_support/all.rb b/activesupport/lib/active_support/all.rb
index 64600575d9059..f537818300bd4 100644
--- a/activesupport/lib/active_support/all.rb
+++ b/activesupport/lib/active_support/all.rb
@@ -1,4 +1,3 @@
 require 'active_support'
-require 'active_support/i18n'
 require 'active_support/time'
 require 'active_support/core_ext'
diff --git a/activesupport/lib/active_support/core_ext/array/conversions.rb b/activesupport/lib/active_support/core_ext/array/conversions.rb
index 814567a5a6b1c..2119322bfe5c1 100644
--- a/activesupport/lib/active_support/core_ext/array/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/array/conversions.rb
@@ -1,7 +1,6 @@
 require 'active_support/core_ext/hash/keys'
 require 'active_support/core_ext/hash/reverse_merge'
 require 'active_support/inflector'
-require 'active_support/i18n'
 
 class Array
   # Converts the array to a comma-separated sentence where the last element is joined by the connector word. Options:
diff --git a/activesupport/lib/active_support/core_ext/string/interpolation.rb b/activesupport/lib/active_support/core_ext/string/interpolation.rb
index 06d3505c60f41..932117cc106cb 100644
--- a/activesupport/lib/active_support/core_ext/string/interpolation.rb
+++ b/activesupport/lib/active_support/core_ext/string/interpolation.rb
@@ -1,91 +1 @@
-=begin
-  heavily based on Masao Mutoh's gettext String interpolation extension
-  http://github.com/mutoh/gettext/blob/f6566738b981fe0952548c421042ad1e0cdfb31e/lib/gettext/core_ext/string.rb
-  Copyright (C) 2005-2010 Masao Mutoh
-  You may redistribute it and/or modify it under the same license terms as Ruby.
-=end
-
-if RUBY_VERSION < '1.9' && !"".respond_to?(:interpolate_without_ruby_19_syntax)
-
-  # KeyError is raised by String#% when the string contains a named placeholder
-  # that is not contained in the given arguments hash. Ruby 1.9 includes and
-  # raises this exception natively. We define it to mimic Ruby 1.9's behaviour
-  # in Ruby 1.8.x
-
-  class KeyError < IndexError
-    def initialize(message = nil)
-      super(message || "key not found")
-    end
-  end unless defined?(KeyError)
-
-  # Extension for String class. This feature is included in Ruby 1.9 or later but not occur TypeError.
-  #
-  # String#% method which accept "named argument". The translator can know
-  # the meaning of the msgids using "named argument" instead of %s/%d style.
-
-  class String
-    alias :interpolate_without_ruby_19_syntax :% # :nodoc:
-
-    INTERPOLATION_PATTERN = Regexp.union(
-      /%%/,
-      /%\{(\w+)\}/,                               # matches placeholders like "%{foo}"
-      /%<(\w+)>(.*?\d*\.?\d*[bBdiouxXeEfgGcps])/  # matches placeholders like "%<foo>.d"
-    )
-
-    # % uses self (i.e. the String) as a format specification and returns the
-    # result of applying it to the given arguments. In other words it interpolates
-    # the given arguments to the string according to the formats the string
-    # defines.
-    #
-    # There are three ways to use it:
-    #
-    # * Using a single argument or Array of arguments.
-    #
-    #   This is the default behaviour of the String class. See Kernel#sprintf for
-    #   more details about the format string.
-    #
-    #   Example:
-    #
-    #     "%d %s" % [1, "message"]
-    #     # => "1 message"
-    #
-    # * Using a Hash as an argument and unformatted, named placeholders.
-    #
-    #   When you pass a Hash as an argument and specify placeholders with %{foo}
-    #   it will interpret the hash values as named arguments.
-    #
-    #   Example:
-    #
-    #     "%{firstname}, %{lastname}" % {:firstname => "Masao", :lastname => "Mutoh"}
-    #     # => "Masao Mutoh"
-    #
-    # * Using a Hash as an argument and formatted, named placeholders.
-    #
-    #   When you pass a Hash as an argument and specify placeholders with %<foo>d
-    #   it will interpret the hash values as named arguments and format the value
-    #   according to the formatting instruction appended to the closing >.
-    #
-    #   Example:
-    #
-    #     "%<integer>d, %<float>.1f" % { :integer => 10, :float => 43.4 }
-    #     # => "10, 43.3"
-    def %(args)
-      if args.kind_of?(Hash)
-        dup.gsub(INTERPOLATION_PATTERN) do |match|
-          if match == '%%'
-            '%'
-          else
-            key = ($1 || $2).to_sym
-            raise KeyError unless args.has_key?(key)
-            $3 ? sprintf("%#{$3}", args[key]) : args[key]
-          end
-        end
-      elsif self =~ INTERPOLATION_PATTERN
-        raise ArgumentError.new('one hash required')
-      else
-        result = gsub(/%([{<])/, '%%\1')
-        result.send :'interpolate_without_ruby_19_syntax', args
-      end
-    end
-  end
-end
+require 'i18n/core_ext/string/interpolate'
diff --git a/activesupport/lib/active_support/dependencies/autoload.rb b/activesupport/lib/active_support/dependencies/autoload.rb
index 44edb89ad58f9..f669f4a77e4b5 100644
--- a/activesupport/lib/active_support/dependencies/autoload.rb
+++ b/activesupport/lib/active_support/dependencies/autoload.rb
@@ -1,7 +1,12 @@
 require "active_support/inflector/methods"
+require "active_support/lazy_load_hooks"
 
 module ActiveSupport
   module Autoload
+    def self.extended(base)
+      base.extend(LazyLoadHooks)
+    end
+
     @@autoloads = {}
     @@under_path = nil
     @@at_path = nil
diff --git a/activesupport/lib/active_support/i18n.rb b/activesupport/lib/active_support/i18n.rb
index 854c60eec1de3..034d7d8ddce48 100644
--- a/activesupport/lib/active_support/i18n.rb
+++ b/activesupport/lib/active_support/i18n.rb
@@ -1,2 +1,3 @@
 require 'i18n'
-I18n.load_path << "#{File.dirname(__FILE__)}/locale/en.yml"
\ No newline at end of file
+I18n.load_path << "#{File.dirname(__FILE__)}/locale/en.yml"
+ActiveSupport.run_base_hooks(:i18n)
\ No newline at end of file
diff --git a/activesupport/lib/active_support/lazy_load_hooks.rb b/activesupport/lib/active_support/lazy_load_hooks.rb
new file mode 100644
index 0000000000000..36acfda52498a
--- /dev/null
+++ b/activesupport/lib/active_support/lazy_load_hooks.rb
@@ -0,0 +1,25 @@
+module ActiveSupport
+  module LazyLoadHooks
+    def _setup_base_hooks
+      @base_hooks ||= Hash.new {|h,k| h[k] = [] }
+      @base ||= {}
+    end
+
+    def base_hook(name = nil, &block)
+      _setup_base_hooks
+
+      if base = @base[name]
+        base.instance_eval(&block)
+      else
+        @base_hooks[name] << block
+      end
+    end
+
+    def run_base_hooks(base, name = nil)
+      _setup_base_hooks
+
+      @base_hooks[name].each { |hook| base.instance_eval(&hook) } if @base_hooks
+      @base[name] = base
+    end
+  end
+end
\ No newline at end of file
diff --git a/activesupport/lib/active_support/railtie.rb b/activesupport/lib/active_support/railtie.rb
index 58d11585bac98..d2c13e030da3d 100644
--- a/activesupport/lib/active_support/railtie.rb
+++ b/activesupport/lib/active_support/railtie.rb
@@ -37,10 +37,12 @@ class Railtie < Rails::Railtie
     config.i18n.load_path = []
 
     initializer "i18n.initialize" do
-      require 'active_support/i18n'
-
-      ActionDispatch::Callbacks.to_prepare do
+      ActiveSupport.base_hook(:i18n) do
         I18n.reload!
+
+        ActionDispatch::Callbacks.to_prepare do
+          I18n.reload!
+        end
       end
     end
 
diff --git a/activesupport/lib/active_support/whiny_nil.rb b/activesupport/lib/active_support/whiny_nil.rb
index 0b68e936f60d7..91ddef26197f3 100644
--- a/activesupport/lib/active_support/whiny_nil.rb
+++ b/activesupport/lib/active_support/whiny_nil.rb
@@ -25,17 +25,16 @@
 # By default it is on in development and test modes, and it is off in production
 # mode.
 class NilClass
-  WHINERS = [::Array]
-  WHINERS << ::ActiveRecord::Base if defined? ::ActiveRecord::Base
-
   METHOD_CLASS_MAP = Hash.new
 
-  WHINERS.each do |klass|
+  def self.add_whiner(klass)
     methods = klass.public_instance_methods - public_instance_methods
     class_name = klass.name
     methods.each { |method| METHOD_CLASS_MAP[method.to_sym] = class_name }
   end
 
+  add_whiner ::Array
+
   # Raises a RuntimeError when you attempt to call +id+ on +nil+.
   def id
     raise RuntimeError, "Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id", caller
diff --git a/activesupport/test/whiny_nil_test.rb b/activesupport/test/whiny_nil_test.rb
index 1e4f8d854a52a..4b9f06deada29 100644
--- a/activesupport/test/whiny_nil_test.rb
+++ b/activesupport/test/whiny_nil_test.rb
@@ -9,6 +9,8 @@ def save!
 require 'abstract_unit'
 require 'active_support/whiny_nil'
 
+NilClass.add_whiner ::ActiveRecord::Base
+
 class WhinyNilTest < Test::Unit::TestCase
   def test_unchanged
     nil.method_thats_not_in_whiners
diff --git a/railties/lib/rails/application/routes_reloader.rb b/railties/lib/rails/application/routes_reloader.rb
index fde6211c5daf0..a5154f4bbac2d 100644
--- a/railties/lib/rails/application/routes_reloader.rb
+++ b/railties/lib/rails/application/routes_reloader.rb
@@ -27,7 +27,7 @@ def reload!
 
         routes.clear!
         paths.each { |path| load(path) }
-        routes.finalize!
+        ActionController.base_hook { routes.finalize! }
 
         nil
       ensure
diff --git a/railties/lib/rails/console/helpers.rb b/railties/lib/rails/console/helpers.rb
index 039db667c40da..212fc6125a20d 100644
--- a/railties/lib/rails/console/helpers.rb
+++ b/railties/lib/rails/console/helpers.rb
@@ -2,4 +2,6 @@ def helper
   @helper ||= ApplicationController.helpers
 end
 
-@controller = ApplicationController.new
+def controller
+  @controller ||= ApplicationController.new
+end
diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index 8f5040ea13480..85b4ff84703bb 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -97,8 +97,8 @@ def load_tasks
 
     initializer :add_view_paths do
       views = paths.app.views.to_a
-      ActionController::Base.prepend_view_path(views) if defined?(ActionController::Base)
-      ActionMailer::Base.prepend_view_path(views) if defined?(ActionMailer::Base)
+      ActionController.base_hook { prepend_view_path(views) } if defined?(ActionController)
+      ActionMailer.base_hook { prepend_view_path(views) } if defined?(ActionMailer)
     end
 
     initializer :add_metals do |app|