A singleton instance of this class is yielded by Inflector#inflections, which can then be used to specify additional inflection rules. Examples:

Inflector.inflections do |inflect|
  inflect.plural %r^(ox)$/, '\1\2en'
  inflect.singular %r^(ox)en/, '\1'

  inflect.irregular 'octopus', 'octopi'

  inflect.uncountable "equipment"
end

New rules are added at the top. So in the example above, the irregular rule for octopus will now be the first of the pluralization and singularization rules that is runs. This guarantees that your rules run before any of the rules that may already have been loaded.

Methods
C
I
N
P
S
U
Included Modules
Attributes
[R] plurals
[R] singulars
[R] uncountables
Class Public methods
new()

Source: show 

# File rails/activesupport/lib/active_support/inflector.rb, line 27
def initialize
  @plurals, @singulars, @uncountables = [], [], []
end
Instance Public methods
clear(scope = :all)

Clears the loaded inflections within a given scope (default is :all). Give the scope as a symbol of the inflection type, the options are: :plurals, :singulars, :uncountables

Examples:

clear :all
clear :plurals

Source: show 

# File rails/activesupport/lib/active_support/inflector.rb, line 70
def clear(scope = :all)
  case scope
    when :all
      @plurals, @singulars, @uncountables = [], [], []
    else
      instance_variable_set "@#{scope}", []
  end
end
irregular(singular, plural)

Specifies a new irregular that applies to both pluralization and singularization at the same time. This can only be used for strings, not regular expressions. You simply pass the irregular in singular and plural form.

Examples:

irregular 'octopus', 'octopi'
irregular 'person', 'people'

Source: show 

# File rails/activesupport/lib/active_support/inflector.rb, line 49
def irregular(singular, plural)
  plural(Regexp.new("(#{singular[0,1]})#{singular[1..-1]}$", "i"), '\1' + plural[1..-1])
  singular(Regexp.new("(#{plural[0,1]})#{plural[1..-1]}$", "i"), '\1' + singular[1..-1])
end
plural(rule, replacement)

Specifies a new pluralization rule and its replacement. The rule can either be a string or a regular expression. The replacement should always be a string that may include references to the matched data from the rule.

Source: show 

# File rails/activesupport/lib/active_support/inflector.rb, line 33
def plural(rule, replacement)
  @plurals.insert(0, [rule, replacement])
end
singular(rule, replacement)

Specifies a new singularization rule and its replacement. The rule can either be a string or a regular expression. The replacement should always be a string that may include references to the matched data from the rule.

Source: show 

# File rails/activesupport/lib/active_support/inflector.rb, line 39
def singular(rule, replacement)
  @singulars.insert(0, [rule, replacement])
end
uncountable(*words)

Add uncountable words that shouldn’t be attempted inflected.

Examples:

uncountable "money"
uncountable "money", "information"
uncountable %w( money information rice )

Source: show 

# File rails/activesupport/lib/active_support/inflector.rb, line 60
def uncountable(*words)
  (@uncountables << words).flatten!
end