# 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, you’ll need to correct it yourself (explained below).

### Public Instance Methods

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

By default, `camelize` converts strings to UpperCamelCase. If the argument to `camelize` is set to `:lower` then `camelize` produces lowerCamelCase.

`camelize` will also convert ‘/’ to ‘::’ which is useful for converting paths to namespaces.

Examples:

    "active_model".camelize                # => "ActiveModel"
    "active_model".camelize(:lower)        # => "activeModel"
    "active_model/errors".camelize         # => "ActiveModel::Errors"
    "active_model/errors".camelize(:lower) # => "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:

    "SSLError".underscore.camelize # => "SslError"

    # File lib/active_support/inflector/methods.rb, line 54
    def camelize(term, uppercase_first_letter = true)
      string = term.to_s
      if uppercase_first_letter
        string = string.sub(%r^[a-z\d]*/) { inflections.acronyms[$&] || $&.capitalize }
      else
        string = string.sub(%r^(?:#{inflections.acronym_regex}(?=\b|[A-Z_])|\w)/) { $&.downcase }
      end
      string.gsub(%r(?:_|(\/))([a-z\d]*)/) { "#{$1}#{inflections.acronyms[$2] || $2.capitalize}" }.gsub('/', '::')
    end

classify(table_name) click to toggle source

Create 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`.)

Examples:

    "egg_and_hams".classify # => "EggAndHam"
    "posts".classify        # => "Post"

Singular names are not handled correctly:

    "business".classify     # => "Busines"

    # File lib/active_support/inflector/methods.rb, line 139
    def classify(table_name)
      # strip out any leading schema name
      camelize(singularize(table_name.to_s.sub(%r.*\./, '')))
    end

constantize(camel_cased_word) click to toggle source

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

    "Module".constantize     # => Module
    "Test::Unit".constantize # => Test::Unit

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'
      "C".constantize # => '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 212
    def constantize(camel_cased_word)
      names = camel_cased_word.split('::')
      names.shift if names.empty? || names.first.empty?

      constant = Object
      names.each do |name|
        constant = constant.const_defined?(name) ? constant.const_get(name) : constant.const_missing(name)
      end
      constant
    end

dasherize(underscored_word) click to toggle source

Replaces underscores with dashes in the string.

Example:

    "puni_puni" # => "puni-puni"

    # File lib/active_support/inflector/methods.rb, line 148
    def dasherize(underscored_word)
      underscored_word.gsub(%r_/, '-')
    end

deconstantize(path) click to toggle source

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

    "Net::HTTP".deconstantize   # => "Net"
    "::Net::HTTP".deconstantize # => "::Net"
    "String".deconstantize      # => ""
    "::String".deconstantize    # => ""
    "".deconstantize            # => ""

See also `demodulize`.

    # File lib/active_support/inflector/methods.rb, line 176
    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:

    "ActiveRecord::CoreExtensions::String::Inflections".demodulize # => "Inflections"
    "Inflections".demodulize                                       # => "Inflections"

See also `deconstantize`.

    # File lib/active_support/inflector/methods.rb, line 158
    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’.

Examples:

    "Message".foreign_key        # => "message_id"
    "Message".foreign_key(false) # => "messageid"
    "Admin::Post".foreign_key    # => "post_id"

    # File lib/active_support/inflector/methods.rb, line 188
    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) click to toggle source

Capitalizes the first word and turns underscores into spaces and strips a trailing “_id”, if any. Like `titleize`, this is meant for creating pretty output.

Examples:

    "employee_salary" # => "Employee salary"
    "author_id"       # => "Author"

    # File lib/active_support/inflector/methods.rb, line 93
    def humanize(lower_case_and_underscored_word)
      result = lower_case_and_underscored_word.to_s.dup
      inflections.humans.each { |(rule, replacement)| break if result.gsub!(rule, replacement) }
      result.gsub!(%r_id$/, "")
      result.gsub!(%r_/, ' ')
      result.gsub(%r([a-z\d]*)/) { |match|
        "#{inflections.acronyms[match] || match.downcase}"
      }.gsub(%r^\w/) { $&.upcase }
    end

inflections() { |instance| ... } click to toggle source

Yields a singleton instance of Inflector::Inflections so you can specify additional inflector rules.

Example:

    ActiveSupport::Inflector.inflections do |inflect|
      inflect.uncountable "rails"
    end

    # File lib/active_support/inflector/inflections.rb, line 164
    def inflections
      if block_given?
        yield Inflections.instance
      else
        Inflections.instance
      end
    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.

Examples:

    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 278
    def ordinalize(number)
      if (11..13).include?(number.to_i.abs % 100)
        "#{number}th"
      else
        case number.to_i.abs % 10
          when 1; "#{number}st"
          when 2; "#{number}nd"
          when 3; "#{number}rd"
          else    "#{number}th"
        end
      end
    end

parameterize(string, sep = '-') click to toggle source

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

#### Examples

    class Person
      def to_param
        "#{id}-#{name.parameterize}"
      end
    end

    @person = Person.find(1)
    # => #<Person id: 1, name: "Donald E. Knuth">

    <%= link_to(@person.name, person_path(@person)) %>
    # => <a href="/person/1-donald-e-knuth">Donald E. Knuth</a>

    # File lib/active_support/inflector/transliterate.rb, line 81
    def parameterize(string, sep = '-')
      # replace accented chars with their ascii equivalents
      parameterized_string = transliterate(string)
      # Turn unwanted chars into the separator
      parameterized_string.gsub!(%r[^a-z0-9\-_]+/, sep)
      unless sep.nil? || sep.empty?
        re_sep = Regexp.escape(sep)
        # No more than one of the separator in a row.
        parameterized_string.gsub!(%r#{re_sep}{2,}/, sep)
        # Remove leading/trailing separator.
        parameterized_string.gsub!(%r^#{re_sep}|#{re_sep}$/, '')
      end
      parameterized_string.downcase
    end

pluralize(word) click to toggle source

Returns the plural form of the word in the string.

Examples:

    "post".pluralize             # => "posts"
    "octopus".pluralize          # => "octopi"
    "sheep".pluralize            # => "sheep"
    "words".pluralize            # => "words"
    "CamelOctopus".pluralize     # => "CamelOctopi"

    # File lib/active_support/inflector/methods.rb, line 23
    def pluralize(word)
      apply_inflections(word, inflections.plurals)
    end

safe_constantize(camel_cased_word) click to toggle source

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

    "Module".safe_constantize     # => Module
    "Test::Unit".safe_constantize # => Test::Unit

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'
      "C".safe_constantize # => 'outside', same as ::C
    end

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

    "blargle".safe_constantize  # => nil
    "UnknownModule".safe_constantize  # => nil
    "UnknownModule::Foo::Bar".safe_constantize  # => nil

    # File lib/active_support/inflector/methods.rb, line 257
    def safe_constantize(camel_cased_word)
      begin
        constantize(camel_cased_word)
      rescue NameError => e
        raise unless e.message =~ %r(uninitialized constant|wrong constant name) #{const_regexp(camel_cased_word)}$/ ||
          e.name.to_s == camel_cased_word.to_s
      rescue ArgumentError => e
        raise unless e.message =~ %rnot missing constant #{const_regexp(camel_cased_word)}\!$/
      end
    end

singularize(word) click to toggle source

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

Examples:

    "posts".singularize            # => "post"
    "octopi".singularize           # => "octopus"
    "sheep".singularize            # => "sheep"
    "word".singularize             # => "word"
    "CamelOctopi".singularize      # => "CamelOctopus"

    # File lib/active_support/inflector/methods.rb, line 35
    def singularize(word)
      apply_inflections(word, inflections.singulars)
    end

tableize(class_name) click to toggle source

Create 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.

Examples

    "RawScaledScorer".tableize # => "raw_scaled_scorers"
    "egg_and_ham".tableize     # => "egg_and_hams"
    "fancyCategory".tableize   # => "fancy_categories"

    # File lib/active_support/inflector/methods.rb, line 125
    def tableize(class_name)
      pluralize(underscore(class_name))
    end

titleize(word) 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.

`titleize` is also aliased as as `titlecase`.

Examples:

    "man from the boondocks".titleize   # => "Man From The Boondocks"
    "x-men: the last stand".titleize    # => "X Men: The Last Stand"
    "TheManWithoutAPast".titleize       # => "The Man Without A Past"
    "raiders_of_the_lost_ark".titleize  # => "Raiders Of The Lost Ark"

    # File lib/active_support/inflector/methods.rb, line 114
    def titleize(word)
      humanize(underscore(word)).gsub(%r\b('?[a-z])/) { $1.capitalize }
    end

transliterate(string, replacement = "?") 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 => lambda {|string| MyTransliterator.transliterate(string)}
      }
    })

Now you can have different transliterations for each locale:

    I18n.locale = :en
    transliterate("Jürgen")
    # => "Jurgen"

    I18n.locale = :de
    transliterate("Jürgen")
    # => "Juergen"

    # File lib/active_support/inflector/transliterate.rb, line 60
    def transliterate(string, replacement = "?")
      I18n.transliterate(ActiveSupport::Multibyte::Unicode.normalize(
        ActiveSupport::Multibyte::Unicode.tidy_bytes(string), :c),
          :replacement => replacement)
    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.

Examples:

    "ActiveModel".underscore         # => "active_model"
    "ActiveModel::Errors".underscore # => "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:

    "SSLError".underscore.camelize # => "SslError"

    # File lib/active_support/inflector/methods.rb, line 76
    def underscore(camel_cased_word)
      word = camel_cased_word.to_s.dup
      word.gsub!(%r::/, '/')
      word.gsub!(%r(?:([A-Za-z\d])|^)(#{inflections.acronym_regex})(?=\b|[^a-z])/) { "#{$1}#{$1 && '_'}#{$2.downcase}" }
      word.gsub!(%r([A-Z\d]+)([A-Z][a-z])/,'\1_\2')
      word.gsub!(%r([a-z\d])([A-Z])/,'\1_\2')
      word.tr!("-", "_")
      word.downcase!
      word
    end