module ActiveSupport::Inflector

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. The default inflections for pluralization, singularization, and uncountable words are kept in inflections.rb.

The Rails core team has stated patches for the inflections library will not be accepted in order to avoid breaking legacy applications which may be relying on errant inflections. If you discover an incorrect inflection and require it for your application or wish to define rules for languages other than English, please correct or add them yourself (explained below).

Constants

ALLOWED_ENCODINGS_FOR_TRANSLITERATE

Public Instance Methods

camelize(term, uppercase_first_letter = true) click to toggle source

Converts strings to UpperCamelCase. If the uppercase_first_letter parameter is set to false, then produces lowerCamelCase.

Also converts '/' to '::' which is useful for converting paths to namespaces.

camelize('active_model')                # => "ActiveModel"
camelize('active_model', false)         # => "activeModel"
camelize('active_model/errors')         # => "ActiveModel::Errors"
camelize('active_model/errors', false)  # => "activeModel::Errors"

As a rule of thumb you can think of camelize as the inverse of underscore, though there are cases where that does not hold:

camelize(underscore('SSLError'))        # => "SslError"
# File lib/active_support/inflector/methods.rb, line 69
def camelize(term, uppercase_first_letter = true)
  string = term.to_s
  # String#camelize takes a symbol (:upper or :lower), so here we also support :lower to keep the methods consistent.
  if !uppercase_first_letter || uppercase_first_letter == :lower
    string = string.sub(inflections.acronyms_camelize_regex) { |match| match.downcase! || match }
  else
    string = string.sub(/^[a-z\d]*/) { |match| inflections.acronyms[match] || match.capitalize! || match }
  end
  string.gsub!(/(?:_|(\/))([a-z\d]*)/i) do
    word = $2
    substituted = inflections.acronyms[word] || word.capitalize! || word
    $1 ? "::#{substituted}" : substituted
  end
  string
end
classify(table_name) click to toggle source

Creates a class name from a plural table name like Rails does for table names to models. Note that this returns a string and not a Class. (To convert to an actual class follow classify with constantize.)

classify('ham_and_eggs') # => "HamAndEgg"
classify('posts')        # => "Post"

Singular names are not handled correctly:

classify('calculus')     # => "Calculu"
# File lib/active_support/inflector/methods.rb, line 206
def classify(table_name)
  # strip out any leading schema name
  camelize(singularize(table_name.to_s.sub(/.*\./, "")))
end
constantize(camel_cased_word) click to toggle source

Tries to find a constant with the name specified in the argument string.

constantize('Module')   # => Module
constantize('Foo::Bar') # => Foo::Bar

The name is assumed to be the one of a top-level constant, no matter whether it starts with “::” or not. No lexical context is taken into account:

C = 'outside'
module M
  C = 'inside'
  C                # => 'inside'
  constantize('C') # => 'outside', same as ::C
end

NameError is raised when the name is not in CamelCase or the constant is unknown.

# File lib/active_support/inflector/methods.rb, line 277
def constantize(camel_cased_word)
  Object.const_get(camel_cased_word)
end
dasherize(underscored_word) click to toggle source

Replaces underscores with dashes in the string.

dasherize('puni_puni') # => "puni-puni"
# File lib/active_support/inflector/methods.rb, line 214
def dasherize(underscored_word)
  underscored_word.tr("_", "-")
end
deconstantize(path) click to toggle source

Removes the rightmost segment from the constant expression in the string.

deconstantize('Net::HTTP')   # => "Net"
deconstantize('::Net::HTTP') # => "::Net"
deconstantize('String')      # => ""
deconstantize('::String')    # => ""
deconstantize('')            # => ""

See also demodulize.

# File lib/active_support/inflector/methods.rb, line 244
def deconstantize(path)
  path.to_s[0, path.rindex("::") || 0] # implementation based on the one in facets' Module#spacename
end
demodulize(path) click to toggle source

Removes the module part from the expression in the string.

demodulize('ActiveSupport::Inflector::Inflections') # => "Inflections"
demodulize('Inflections')                           # => "Inflections"
demodulize('::Inflections')                         # => "Inflections"
demodulize('')                                      # => ""

See also deconstantize.

# File lib/active_support/inflector/methods.rb, line 226
def demodulize(path)
  path = path.to_s
  if i = path.rindex("::")
    path[(i + 2)..-1]
  else
    path
  end
end
foreign_key(class_name, separate_class_name_and_id_with_underscore = true) click to toggle source

Creates a foreign key name from a class name. separate_class_name_and_id_with_underscore sets whether the method should put '_' between the name and 'id'.

foreign_key('Message')        # => "message_id"
foreign_key('Message', false) # => "messageid"
foreign_key('Admin::Post')    # => "post_id"
# File lib/active_support/inflector/methods.rb, line 255
def foreign_key(class_name, separate_class_name_and_id_with_underscore = true)
  underscore(demodulize(class_name)) + (separate_class_name_and_id_with_underscore ? "_id" : "id")
end
humanize(lower_case_and_underscored_word, capitalize: true, keep_id_suffix: false) click to toggle source

Tweaks an attribute name for display to end users.

Specifically, performs these transformations:

  • Applies human inflection rules to the argument.

  • Deletes leading underscores, if any.

  • Removes an “_id” suffix if present.

  • Replaces underscores with spaces, if any.

  • Downcases all words except acronyms.

  • Capitalizes the first word.

The capitalization of the first word can be turned off by setting the :capitalize option to false (default is true).

The trailing '_id' can be kept and capitalized by setting the optional parameter keep_id_suffix to true (default is false).

humanize('employee_salary')                  # => "Employee salary"
humanize('author_id')                        # => "Author"
humanize('author_id', capitalize: false)     # => "author"
humanize('_id')                              # => "Id"
humanize('author_id', keep_id_suffix: true)  # => "Author id"

If “SSL” was defined to be an acronym:

humanize('ssl_error') # => "SSL error"
# File lib/active_support/inflector/methods.rb, line 132
def humanize(lower_case_and_underscored_word, capitalize: true, keep_id_suffix: false)
  result = lower_case_and_underscored_word.to_s.dup

  inflections.humans.each { |(rule, replacement)| break if result.sub!(rule, replacement) }

  result.tr!("_", " ")
  result.lstrip!
  if !keep_id_suffix && lower_case_and_underscored_word&.end_with?("_id")
    result.delete_suffix!(" id")
  end

  result.gsub!(/([a-z\d]+)/i) do |match|
    match.downcase!
    inflections.acronyms[match] || match
  end

  if capitalize
    result.sub!(/\A\w/) do |match|
      match.upcase!
      match
    end
  end

  result
end
inflections(locale = :en) { |instance| ... } click to toggle source

Yields a singleton instance of Inflector::Inflections so you can specify additional inflector rules. If passed an optional locale, rules for other languages can be specified. If not specified, defaults to :en. Only rules for English are provided.

ActiveSupport::Inflector.inflections(:en) do |inflect|
  inflect.uncountable 'rails'
end
# File lib/active_support/inflector/inflections.rb, line 263
def inflections(locale = :en)
  if block_given?
    yield Inflections.instance(locale)
  else
    Inflections.instance_or_fallback(locale)
  end
end
ordinal(number) click to toggle source

Returns the suffix that should be added to a number to denote the position in an ordered sequence such as 1st, 2nd, 3rd, 4th.

ordinal(1)     # => "st"
ordinal(2)     # => "nd"
ordinal(1002)  # => "nd"
ordinal(1003)  # => "rd"
ordinal(-11)   # => "th"
ordinal(-1021) # => "st"
# File lib/active_support/inflector/methods.rb, line 322
def ordinal(number)
  I18n.translate("number.nth.ordinals", number: number)
end
ordinalize(number) click to toggle source

Turns a number into an ordinal string used to denote the position in an ordered sequence such as 1st, 2nd, 3rd, 4th.

ordinalize(1)     # => "1st"
ordinalize(2)     # => "2nd"
ordinalize(1002)  # => "1002nd"
ordinalize(1003)  # => "1003rd"
ordinalize(-11)   # => "-11th"
ordinalize(-1021) # => "-1021st"
# File lib/active_support/inflector/methods.rb, line 335
def ordinalize(number)
  I18n.translate("number.nth.ordinalized", number: number)
end
parameterize(string, separator: "-", preserve_case: false, locale: nil) click to toggle source

Replaces special characters in a string so that it may be used as part of a 'pretty' URL.

parameterize("Donald E. Knuth") # => "donald-e-knuth"
parameterize("^très|Jolie-- ")  # => "tres-jolie"

To use a custom separator, override the separator argument.

parameterize("Donald E. Knuth", separator: '_') # => "donald_e_knuth"
parameterize("^très|Jolie__ ", separator: '_')  # => "tres_jolie"

To preserve the case of the characters in a string, use the preserve_case argument.

parameterize("Donald E. Knuth", preserve_case: true) # => "Donald-E-Knuth"
parameterize("^très|Jolie-- ", preserve_case: true) # => "tres-Jolie"

It preserves dashes and underscores unless they are used as separators:

parameterize("^très|Jolie__ ")                 # => "tres-jolie__"
parameterize("^très|Jolie-- ", separator: "_") # => "tres_jolie--"
parameterize("^très_Jolie-- ", separator: ".") # => "tres_jolie--"

If the optional parameter locale is specified, the word will be parameterized as a word of that language. By default, this parameter is set to nil and it will use the configured I18n.locale.

# File lib/active_support/inflector/transliterate.rb, line 121
def parameterize(string, separator: "-", preserve_case: false, locale: nil)
  # Replace accented chars with their ASCII equivalents.
  parameterized_string = transliterate(string, locale: locale)

  # Turn unwanted chars into the separator.
  parameterized_string.gsub!(/[^a-z0-9\-_]+/i, separator)

  unless separator.nil? || separator.empty?
    if separator == "-"
      re_duplicate_separator        = /-{2,}/
      re_leading_trailing_separator = /^-|-$/i
    else
      re_sep = Regexp.escape(separator)
      re_duplicate_separator        = /#{re_sep}{2,}/
      re_leading_trailing_separator = /^#{re_sep}|#{re_sep}$/i
    end
    # No more than one of the separator in a row.
    parameterized_string.gsub!(re_duplicate_separator, separator)
    # Remove leading/trailing separator.
    parameterized_string.gsub!(re_leading_trailing_separator, "")
  end

  parameterized_string.downcase! unless preserve_case
  parameterized_string
end
pluralize(word, locale = :en) click to toggle source

Returns the plural form of the word in the string.

If passed an optional locale parameter, the word will be pluralized using rules defined for that language. By default, this parameter is set to :en.

pluralize('post')             # => "posts"
pluralize('octopus')          # => "octopi"
pluralize('sheep')            # => "sheep"
pluralize('words')            # => "words"
pluralize('CamelOctopus')     # => "CamelOctopi"
pluralize('ley', :es)         # => "leyes"
# File lib/active_support/inflector/methods.rb, line 32
def pluralize(word, locale = :en)
  apply_inflections(word, inflections(locale).plurals, locale)
end
safe_constantize(camel_cased_word) click to toggle source

Tries to find a constant with the name specified in the argument string.

safe_constantize('Module')   # => Module
safe_constantize('Foo::Bar') # => Foo::Bar

The name is assumed to be the one of a top-level constant, no matter whether it starts with “::” or not. No lexical context is taken into account:

C = 'outside'
module M
  C = 'inside'
  C                     # => 'inside'
  safe_constantize('C') # => 'outside', same as ::C
end

nil is returned when the name is not in CamelCase or the constant (or part of it) is unknown.

safe_constantize('blargle')                  # => nil
safe_constantize('UnknownModule')            # => nil
safe_constantize('UnknownModule::Foo::Bar')  # => nil
# File lib/active_support/inflector/methods.rb, line 303
def safe_constantize(camel_cased_word)
  constantize(camel_cased_word)
rescue NameError => e
  raise if e.name && !(camel_cased_word.to_s.split("::").include?(e.name.to_s) ||
    e.name.to_s == camel_cased_word.to_s)
rescue LoadError => e
  message = e.respond_to?(:original_message) ? e.original_message : e.message
  raise unless /Unable to autoload constant #{const_regexp(camel_cased_word)}/.match?(message)
end
singularize(word, locale = :en) click to toggle source

The reverse of pluralize, returns the singular form of a word in a string.

If passed an optional locale parameter, the word will be singularized using rules defined for that language. By default, this parameter is set to :en.

singularize('posts')            # => "post"
singularize('octopi')           # => "octopus"
singularize('sheep')            # => "sheep"
singularize('word')             # => "word"
singularize('CamelOctopi')      # => "CamelOctopus"
singularize('leyes', :es)       # => "ley"
# File lib/active_support/inflector/methods.rb, line 49
def singularize(word, locale = :en)
  apply_inflections(word, inflections(locale).singulars, locale)
end
tableize(class_name) click to toggle source

Creates the name of a table like Rails does for models to table names. This method uses the pluralize method on the last word in the string.

tableize('RawScaledScorer') # => "raw_scaled_scorers"
tableize('ham_and_egg')     # => "ham_and_eggs"
tableize('fancyCategory')   # => "fancy_categories"
# File lib/active_support/inflector/methods.rb, line 192
def tableize(class_name)
  pluralize(underscore(class_name))
end
titleize(word, keep_id_suffix: false) click to toggle source

Capitalizes all the words and replaces some characters in the string to create a nicer looking title. titleize is meant for creating pretty output. It is not used in the Rails internals.

The trailing '_id','Id'.. can be kept and capitalized by setting the optional parameter keep_id_suffix to true. By default, this parameter is false.

titleize('man from the boondocks')                       # => "Man From The Boondocks"
titleize('x-men: the last stand')                        # => "X Men: The Last Stand"
titleize('TheManWithoutAPast')                           # => "The Man Without A Past"
titleize('raiders_of_the_lost_ark')                      # => "Raiders Of The Lost Ark"
titleize('string_ending_with_id', keep_id_suffix: true)  # => "String Ending With Id"
# File lib/active_support/inflector/methods.rb, line 180
def titleize(word, keep_id_suffix: false)
  humanize(underscore(word), keep_id_suffix: keep_id_suffix).gsub(/\b(?<!\w['’`()])[a-z]/) do |match|
    match.capitalize
  end
end
transliterate(string, replacement = "?", locale: nil) click to toggle source

Replaces non-ASCII characters with an ASCII approximation, or if none exists, a replacement character which defaults to “?”.

transliterate('Ærøskøbing')
# => "AEroskobing"

Default approximations are provided for Western/Latin characters, e.g, “ø”, “ñ”, “é”, “ß”, etc.

This method is I18n aware, so you can set up custom approximations for a locale. This can be useful, for example, to transliterate German's “ü” and “ö” to “ue” and “oe”, or to add support for transliterating Russian to ASCII.

In order to make your custom transliterations available, you must set them as the i18n.transliterate.rule i18n key:

# Store the transliterations in locales/de.yml
i18n:
  transliterate:
    rule:
      ü: "ue"
      ö: "oe"

# Or set them using Ruby
I18n.backend.store_translations(:de, i18n: {
  transliterate: {
    rule: {
      'ü' => 'ue',
      'ö' => 'oe'
    }
  }
})

The value for i18n.transliterate.rule can be a simple Hash that maps characters to ASCII approximations as shown above, or, for more complex requirements, a Proc:

I18n.backend.store_translations(:de, i18n: {
  transliterate: {
    rule: ->(string) { MyTransliterator.transliterate(string) }
  }
})

Now you can have different transliterations for each locale:

transliterate('Jürgen', locale: :en)
# => "Jurgen"

transliterate('Jürgen', locale: :de)
# => "Juergen"

Transliteration is restricted to UTF-8, US-ASCII, and GB18030 strings. Other encodings will raise an ArgumentError.

# File lib/active_support/inflector/transliterate.rb, line 64
def transliterate(string, replacement = "?", locale: nil)
  string = string.dup if string.frozen?
  raise ArgumentError, "Can only transliterate strings. Received #{string.class.name}" unless string.is_a?(String)
  raise ArgumentError, "Cannot transliterate strings with #{string.encoding} encoding" unless ALLOWED_ENCODINGS_FOR_TRANSLITERATE.include?(string.encoding)

  input_encoding = string.encoding

  # US-ASCII is a subset of UTF-8 so we'll force encoding as UTF-8 if
  # US-ASCII is given. This way we can let tidy_bytes handle the string
  # in the same way as we do for UTF-8
  string.force_encoding(Encoding::UTF_8) if string.encoding == Encoding::US_ASCII

  # GB18030 is Unicode compatible but is not a direct mapping so needs to be
  # transcoded. Using invalid/undef :replace will result in loss of data in
  # the event of invalid characters, but since tidy_bytes will replace
  # invalid/undef with a "?" we're safe to do the same beforehand
  string.encode!(Encoding::UTF_8, invalid: :replace, undef: :replace) if string.encoding == Encoding::GB18030

  transliterated = I18n.transliterate(
    ActiveSupport::Multibyte::Unicode.tidy_bytes(string).unicode_normalize(:nfc),
    replacement: replacement,
    locale: locale
  )

  # Restore the string encoding of the input if it was not UTF-8.
  # Apply invalid/undef :replace as tidy_bytes does
  transliterated.encode!(input_encoding, invalid: :replace, undef: :replace) if input_encoding != transliterated.encoding

  transliterated
end
underscore(camel_cased_word) click to toggle source

Makes an underscored, lowercase form from the expression in the string.

Changes '::' to '/' to convert namespaces to paths.

underscore('ActiveModel')         # => "active_model"
underscore('ActiveModel::Errors') # => "active_model/errors"

As a rule of thumb you can think of underscore as the inverse of camelize, though there are cases where that does not hold:

camelize(underscore('SSLError'))  # => "SslError"
# File lib/active_support/inflector/methods.rb, line 96
def underscore(camel_cased_word)
  return camel_cased_word.to_s unless /[A-Z-]|::/.match?(camel_cased_word)
  word = camel_cased_word.to_s.gsub("::", "/")
  word.gsub!(inflections.acronyms_underscore_regex) { "#{$1 && '_' }#{$2.downcase}" }
  word.gsub!(/([A-Z])(?=[A-Z][a-z])|([a-z\d])(?=[A-Z])/) { ($1 || $2) << "_" }
  word.tr!("-", "_")
  word.downcase!
  word
end
upcase_first(string) click to toggle source

Converts just the first character to uppercase.

upcase_first('what a Lovely Day') # => "What a Lovely Day"
upcase_first('w')                 # => "W"
upcase_first('')                  # => ""
# File lib/active_support/inflector/methods.rb, line 163
def upcase_first(string)
  string.length > 0 ? string[0].upcase.concat(string[1..-1]) : ""
end

Private Instance Methods

apply_inflections(word, rules, locale = :en) click to toggle source

Applies inflection rules for singularize and pluralize.

If passed an optional locale parameter, the uncountables will be found for that locale.

apply_inflections('post', inflections.plurals, :en)    # => "posts"
apply_inflections('posts', inflections.singulars, :en) # => "post"
# File lib/active_support/inflector/methods.rb, line 364
def apply_inflections(word, rules, locale = :en)
  result = word.to_s.dup

  if word.empty? || inflections(locale).uncountables.uncountable?(result)
    result
  else
    rules.each { |(rule, replacement)| break if result.sub!(rule, replacement) }
    result
  end
end
const_regexp(camel_cased_word) click to toggle source

Mounts a regular expression, returned as a string to ease interpolation, that will match part by part the given constant.

const_regexp("Foo::Bar::Baz") # => "Foo(::Bar(::Baz)?)?"
const_regexp("::")            # => "::"
# File lib/active_support/inflector/methods.rb, line 345
def const_regexp(camel_cased_word)
  parts = camel_cased_word.split("::")

  return Regexp.escape(camel_cased_word) if parts.blank?

  last = parts.pop

  parts.reverse!.inject(last) do |acc, part|
    part.empty? ? acc : "#{part}(::#{acc})?"
  end
end