rails--rails/activesupport/lib/active_support/inflector.rb

# The Inflector transforms words from singular to plural, class names to table names, modularized class names to ones without,
# and class names to foreign keys.
module Inflector 
  extend self

  def pluralize(word)
    result = word.to_s.dup
    plural_rules.each do |(rule, replacement)|
      break if result.gsub!(rule, replacement)
    end
    return result
  end

  def singularize(word)
    result = word.to_s.dup
    singular_rules.each do |(rule, replacement)|
      break if result.gsub!(rule, replacement)
    end
    return result
  end

  def camelize(lower_case_and_underscored_word)
    lower_case_and_underscored_word.to_s.gsub(/\/(.?)/) { "::" + $1.upcase }.gsub(/(^|_)(.)/) { $2.upcase }
  end
  
  def underscore(camel_cased_word)
    camel_cased_word.to_s.gsub(/::/, '/').gsub(/([A-Z]+)([A-Z])/,'\1_\2').gsub(/([a-z])([A-Z])/,'\1_\2').downcase
  end

  def humanize(lower_case_and_underscored_word)
    lower_case_and_underscored_word.to_s.gsub(/_/, " ").capitalize
  end

  def demodulize(class_name_in_module)
    class_name_in_module.to_s.gsub(/^.*::/, '')
  end

  def tableize(class_name)
    pluralize(underscore(class_name))
  end
  
  def classify(table_name)
    camelize(singularize(table_name))
  end

  def foreign_key(class_name, separate_class_name_and_id_with_underscore = true)
    Inflector.underscore(Inflector.demodulize(class_name)) + 
      (separate_class_name_and_id_with_underscore ? "_id" : "id")
  end

  def constantize(camel_cased_word)
    camel_cased_word.split("::").inject(Object) do |final_type, part| 
      final_type = final_type.const_get(part)
    end
  end

  private
    def plural_rules #:doc:
      [
        [/(fish)$/i, '\1\2'],                 # fish
        [/(x|ch|ss|sh)$/i, '\1es'],           # search, switch, fix, box, process, address
        [/(series)$/i, '\1\2'],
        [/([^aeiouy]|qu)ies$/i, '\1y'],
        [/([^aeiouy]|qu)y$/i, '\1ies'],       # query, ability, agency
        [/(?:([^f])fe|([lr])f)$/i, '\1\2ves'], # half, safe, wife
        [/sis$/i, 'ses'],                     # basis, diagnosis
        [/([ti])um$/i, '\1a'],                # datum, medium
        [/(p)erson$/i, '\1\2eople'],          # person, salesperson
        [/(m)an$/i, '\1\2en'],                # man, woman, spokesman
        [/(c)hild$/i, '\1\2hildren'],         # child
        [/s$/i, 's'],                         # no change (compatibility)
        [/$/, 's']
      ]
    end

    def singular_rules #:doc:
      [
        [/(f)ish$/i, '\1\2ish'],
        [/(x|ch|ss|sh)es$/i, '\1'],
        [/(m)ovies$/i, '\1\2ovie'],
        [/(s)eries$/i, '\1\2eries'],
        [/([^aeiouy]|qu)ies$/i, '\1y'],
        [/([lr])ves$/i, '\1f'],
        [/([^f])ves$/i, '\1fe'],
        [/((a)naly|(b)a|(d)iagno|(p)arenthe|(p)rogno|(s)ynop|(t)he)ses$/i, '\1\2sis'],
        [/([ti])a$/i, '\1um'],
        [/(p)eople$/i, '\1\2erson'],
        [/(m)en$/i, '\1\2an'],
        [/(s)tatus$/i, '\1\2tatus'],
        [/(c)hildren$/i, '\1\2hild'],
        [/(n)ews$/i, '\1\2ews'],
        [/s$/i, '']
      ]
    end
end