Can't get pluralize/singularize working with ActiveSupport::Inflector (in irb)

irb(main):001:0> require 'active_support'
=> true
irb(main):002:0> require 'active_support/inflector/inflections'
=> true
irb(main):003:0> ActiveSupport::Inflector.pluralize('test')
=> "test"
irb(main):004:0> ActiveSupport::Inflector.singularize('tests')
=> "tests"
irb(main):005:0> ActiveSupport::Inflector.titleize('hat simulator')
=> "Hat 开发者_运维技巧Simulator"
<ort::Inflector.tableize("america's number one hat simulator")
=> "america's number one hat simulator"

Well, basically, that's the question. It's confusing me that methods such as titleize seem to work fine, but tableize, pluralize and singularize don't.

Have I forgotten to require something?

(On a separate note, I notice this page provides examples like "post".pluralize, which when I tried, resulted in NoMethodError: undefined method 'pluralize' for "post":String. But maybe that's something to save for another question.)

Access to #pluralize without adding new methods to the String class:

require 'active_support/inflector'
ActiveSupport::Inflector.pluralize('test')
#=> "tests"

For String class:

require 'active_support/core_ext/string'
"test".pluralize
#=> "tests"

which actually calls ActiveSupport::Inflector.pluralize underneath:

def pluralize
  ActiveSupport::Inflector.pluralize(self)
end