cache.rb requires active_support/core_ext/string/inflections because it uses camelize

activesupport/lib/active_support/cache.rb

@@ -4,6 +4,7 @@
 require 'active_support/core_ext/exception'
 require 'active_support/core_ext/class/attribute_accessors'
 require 'active_support/core_ext/object/to_param'
+require 'active_support/core_ext/string/inflections'
 
 module ActiveSupport
   # See ActiveSupport::Cache::Store for documentation.