Chars enables you to work transparently with UTF-8 encoding in the Ruby String class without having extensive knowledge about the encoding. A Chars object accepts a string upon initialization and proxies String methods in an encoding safe manner. All the normal String methods are also implemented on the proxy.

String methods are proxied through the Chars object, and can be accessed through the mb_chars method. Methods which would normally return a String object now return a Chars object so methods can be chained.

"The Perfect String  ".mb_chars.downcase.strip.normalize # => "the perfect string"

Chars objects are perfectly interchangeable with String objects as long as no explicit class checks are made. If certain methods do explicitly check the class, call to_s before you pass chars objects to them.

bad.explicit_checking_method "T".mb_chars.downcase.to_s

The default Chars implementation assumes that the encoding of the string is UTF-8, if you want to handle different encodings you can write your own multibyte string handler and configure it through ActiveSupport::Multibyte.proxy_class.

class CharsForUTF32
  def size
    @wrapped_string.size / 4
  end

  def self.accepts?(string)
    string.length % 4 == 0
  end
end

ActiveSupport::Multibyte.proxy_class = CharsForUTF32
Methods
#
A
C
D
G
I
L
M
N
O
R
S
T
U
W
Included Modules
Attributes
[R] to_s
[R] to_str
[R] wrapped_string
Class Public methods
consumes?(string)

Returns true when the proxy class can handle the string. Returns false otherwise.

# File activesupport/lib/active_support/multibyte/chars.rb, line 75
def self.consumes?(string)
  # Unpack is a little bit faster than regular expressions.
  string.unpack('U*')
  true
rescue ArgumentError
  false
end
new(string)

Creates a new Chars instance by wrapping string.

# File activesupport/lib/active_support/multibyte/chars.rb, line 42
def initialize(string)
  @wrapped_string = string
  @wrapped_string.force_encoding(Encoding::UTF_8) unless @wrapped_string.frozen?
end
wants?(string)

Returns true if the Chars class can and should act as a proxy for the string string. Returns false otherwise.

# File activesupport/lib/active_support/multibyte/chars.rb, line 99
def self.wants?(string)
  $KCODE == 'UTF8' && consumes?(string)
end
Instance Public methods
+(other)

Returns a new Chars object containing the other object concatenated to the string.

Example:

('Café'.mb_chars + ' périferôl').to_s # => "Café périferôl"
# File activesupport/lib/active_support/multibyte/chars.rb, line 107
def +(other)
  chars(@wrapped_string + other)
end
<=>(other)

Returns -1, 0, or 1, depending on whether the Chars object is to be sorted before, equal or after the object on the right side of the operation. It accepts any object that implements to_s:

'é'.mb_chars <=> 'ü'.mb_chars # => -1

See String#<=> for more details.

# File activesupport/lib/active_support/multibyte/chars.rb, line 92
def <=>(other)
  @wrapped_string <=> other.to_s
end
=~(other)

Like String#=~ only it returns the character offset (in codepoints) instead of the byte offset.

Example:

'Café périferôl'.mb_chars =~ %rô/ # => 12
# File activesupport/lib/active_support/multibyte/chars.rb, line 115
def =~(other)
  translate_offset(@wrapped_string =~ other)
end
[](*args)
[]=(*args)

Like String#[]=, except instead of byte offsets you specify character offsets.

Example:

s = "Müller"
s.mb_chars[2] = "e" # Replace character with offset 2
s
# => "Müeler"

s = "Müller"
s.mb_chars[1, 2] = "ö" # Replace 2 characters at character offset 1
s
# => "Möler"
# File activesupport/lib/active_support/multibyte/chars.rb, line 265
def []=(*args)
  replace_by = args.pop
  # Indexed replace with regular expressions already works
  if args.first.is_a?(Regexp)
    @wrapped_string[*args] = replace_by
  else
    result = Unicode.u_unpack(@wrapped_string)
    case args.first
    when Fixnum
      raise IndexError, "index #{args[0]} out of string" if args[0] >= result.length
      min = args[0]
      max = args[1].nil? ? min : (min + args[1] - 1)
      range = Range.new(min, max)
      replace_by = [replace_by].pack('U') if replace_by.is_a?(Fixnum)
    when Range
      raise RangeError, "#{args[0]} out of range" if args[0].min >= result.length
      range = args[0]
    else
      needle = args[0].to_s
      min = index(needle)
      max = min + Unicode.u_unpack(needle).length - 1
      range = Range.new(min, max)
    end
    result[range] = Unicode.u_unpack(replace_by)
    @wrapped_string.replace(result.pack('U*'))
  end
end
acts_like_string?()

Enable more predictable duck-typing on String-like classes. See Object#acts_like?.

# File activesupport/lib/active_support/multibyte/chars.rb, line 70
def acts_like_string?
  true
end
capitalize()

Converts the first character to uppercase and the remainder to lowercase.

Example:

'über'.mb_chars.capitalize.to_s # => "Über"
# File activesupport/lib/active_support/multibyte/chars.rb, line 358
def capitalize
  (slice(0) || chars('')).upcase + (slice(1..-1) || chars('')).downcase
end
center(integer, padstr=' ')

Works just like String#center, only integer specifies characters instead of bytes.

Example:

"¾ cup".mb_chars.center(8).to_s
# => " ¾ cup  "

"¾ cup".mb_chars.center(8, " ").to_s # Use non-breaking whitespace
# => " ¾ cup  "
# File activesupport/lib/active_support/multibyte/chars.rb, line 233
def center(integer, padstr=' ')
  justify(integer, :center, padstr)
end
compose()

Performs composition on all the characters.

Example:

'é'.length                       # => 3
'é'.mb_chars.compose.to_s.length # => 2
# File activesupport/lib/active_support/multibyte/chars.rb, line 396
def compose
  chars(Unicode.compose_codepoints(Unicode.u_unpack(@wrapped_string)).pack('U*'))
end
decompose()

Performs canonical decomposition on all the characters.

Example:

'é'.length                         # => 2
'é'.mb_chars.decompose.to_s.length # => 3
# File activesupport/lib/active_support/multibyte/chars.rb, line 387
def decompose
  chars(Unicode.decompose_codepoints(:canonical, Unicode.u_unpack(@wrapped_string)).pack('U*'))
end
downcase()

Convert characters in the string to lowercase.

Example:

'VĚDA A VÝZKUM'.mb_chars.downcase.to_s # => "věda a výzkum"
# File activesupport/lib/active_support/multibyte/chars.rb, line 350
def downcase
  chars(Unicode.apply_mapping @wrapped_string, :lowercase_mapping)
end
g_length()

Returns the number of grapheme clusters in the string.

Example:

'क्षि'.mb_chars.length   # => 4
'क्षि'.mb_chars.g_length # => 3
# File activesupport/lib/active_support/multibyte/chars.rb, line 405
def g_length
  Unicode.g_unpack(@wrapped_string).length
end
include?(other)

Returns true if contained string contains other. Returns false otherwise.

Example:

'Café'.mb_chars.include?('é') # => true
# File activesupport/lib/active_support/multibyte/chars.rb, line 139
def include?(other)
  # We have to redefine this method because Enumerable defines it.
  @wrapped_string.include?(other)
end
index(needle, offset=0)

Returns the position needle in the string, counting in codepoints. Returns nil if needle isn’t found.

Example:

'Café périferôl'.mb_chars.index('ô')   # => 12
'Café périferôl'.mb_chars.index(%r\w/) # => 0
# File activesupport/lib/active_support/multibyte/chars.rb, line 149
def index(needle, offset=0)
  wrapped_offset = first(offset).wrapped_string.length
  index = @wrapped_string.index(needle, wrapped_offset)
  index ? (Unicode.u_unpack(@wrapped_string.slice(0...index)).size) : nil
end
insert(offset, fragment)

Inserts the passed string at specified codepoint offsets.

Example:

'Café'.mb_chars.insert(4, ' périferôl').to_s # => "Café périferôl"
# File activesupport/lib/active_support/multibyte/chars.rb, line 123
def insert(offset, fragment)
  unpacked = Unicode.u_unpack(@wrapped_string)
  unless offset > unpacked.length
    @wrapped_string.replace(
      Unicode.u_unpack(@wrapped_string).insert(offset, *Unicode.u_unpack(fragment)).pack('U*')
    )
  else
    raise IndexError, "index #{offset} out of string"
  end
  self
end
limit(limit)

Limit the byte size of the string to a number of bytes without breaking characters. Usable when the storage for a string is limited for some reason.

Example:

'こんにちは'.mb_chars.limit(7).to_s # => "こん"
# File activesupport/lib/active_support/multibyte/chars.rb, line 334
def limit(limit)
  slice(0...translate_offset(limit))
end
ljust(integer, padstr=' ')

Works just like String#ljust, only integer specifies characters instead of bytes.

Example:

"¾ cup".mb_chars.rjust(8).to_s
# => "¾ cup   "

"¾ cup".mb_chars.rjust(8, " ").to_s # Use non-breaking whitespace
# => "¾ cup   "
# File activesupport/lib/active_support/multibyte/chars.rb, line 220
def ljust(integer, padstr=' ')
  justify(integer, :left, padstr)
end
lstrip()

Strips entire range of Unicode whitespace from the left of the string.

# File activesupport/lib/active_support/multibyte/chars.rb, line 181
def lstrip
  chars(@wrapped_string.gsub(Unicode::LEADERS_PAT, ''))
end
method_missing(method, *args, &block)

Forward all undefined methods to the wrapped string.

# File activesupport/lib/active_support/multibyte/chars.rb, line 53
def method_missing(method, *args, &block)
  if method.to_s =~ %r!$/
    @wrapped_string.__send__(method, *args, &block)
    self
  else
    result = @wrapped_string.__send__(method, *args, &block)
    result.kind_of?(String) ? chars(result) : result
  end
end
normalize(form = nil)

Returns the KC normalization of the string by default. NFKC is considered the best normalization form for passing strings to databases and validations.

# File activesupport/lib/active_support/multibyte/chars.rb, line 378
def normalize(form = nil)
  chars(Unicode.normalize(@wrapped_string, form))
end
ord()

Returns the codepoint of the first character in the string.

Example:

'こんにちは'.mb_chars.ord # => 12371
# File activesupport/lib/active_support/multibyte/chars.rb, line 194
def ord
  Unicode.u_unpack(@wrapped_string)[0]
end
respond_to?(method, include_private=false)

Returns true if obj responds to the given method. Private methods are included in the search only if the optional second parameter evaluates to true.

# File activesupport/lib/active_support/multibyte/chars.rb, line 65
def respond_to?(method, include_private=false)
  super || @wrapped_string.respond_to?(method, include_private)
end
reverse()

Reverses all characters in the string.

Example:

'Café'.mb_chars.reverse.to_s # => 'éfaC'
# File activesupport/lib/active_support/multibyte/chars.rb, line 297
def reverse
  chars(Unicode.g_unpack(@wrapped_string).reverse.flatten.pack('U*'))
end
rindex(needle, offset=nil)

Returns the position needle in the string, counting in codepoints, searching backward from offset or the end of the string. Returns nil if needle isn’t found.

Example:

'Café périferôl'.mb_chars.rindex('é')   # => 6
'Café périferôl'.mb_chars.rindex(%r\w/) # => 13
# File activesupport/lib/active_support/multibyte/chars.rb, line 162
def rindex(needle, offset=nil)
  offset ||= length
  wrapped_offset = first(offset).wrapped_string.length
  index = @wrapped_string.rindex(needle, wrapped_offset)
  index ? (Unicode.u_unpack(@wrapped_string.slice(0...index)).size) : nil
end
rjust(integer, padstr=' ')

Works just like String#rjust, only integer specifies characters instead of bytes.

Example:

"¾ cup".mb_chars.rjust(8).to_s
# => "   ¾ cup"

"¾ cup".mb_chars.rjust(8, " ").to_s # Use non-breaking whitespace
# => "   ¾ cup"
# File activesupport/lib/active_support/multibyte/chars.rb, line 207
def rjust(integer, padstr=' ')
  justify(integer, :right, padstr)
end
rstrip()

Strips entire range of Unicode whitespace from the right of the string.

# File activesupport/lib/active_support/multibyte/chars.rb, line 176
def rstrip
  chars(@wrapped_string.gsub(Unicode::TRAILERS_PAT, ''))
end
size()

Returns the number of codepoints in the string

# File activesupport/lib/active_support/multibyte/chars.rb, line 170
def size
  Unicode.u_unpack(@wrapped_string).size
end
slice(*args)

Implements Unicode-aware slice with codepoints. Slicing on one point returns the codepoints for that character.

Example:

'こんにちは'.mb_chars.slice(2..3).to_s # => "にち"
Also aliased as: []
# File activesupport/lib/active_support/multibyte/chars.rb, line 306
def slice(*args)
  if args.size > 2
    raise ArgumentError, "wrong number of arguments (#{args.size} for 1)" # Do as if we were native
  elsif (args.size == 2 && !(args.first.is_a?(Numeric) || args.first.is_a?(Regexp)))
    raise TypeError, "cannot convert #{args.first.class} into Integer" # Do as if we were native
  elsif (args.size == 2 && !args[1].is_a?(Numeric))
    raise TypeError, "cannot convert #{args[1].class} into Integer" # Do as if we were native
  elsif args[0].kind_of? Range
    cps = Unicode.u_unpack(@wrapped_string).slice(*args)
    result = cps.nil? ? nil : cps.pack('U*')
  elsif args[0].kind_of? Regexp
    result = @wrapped_string.slice(*args)
  elsif args.size == 1 && args[0].kind_of?(Numeric)
    character = Unicode.u_unpack(@wrapped_string)[args[0]]
    result = character && [character].pack('U')
  else
    cps = Unicode.u_unpack(@wrapped_string).slice(*args)
    result = cps && cps.pack('U*')
  end
  result && chars(result)
end
split(*args)

Works just like String#split, with the exception that the items in the resulting list are Chars instances instead of String. This makes chaining methods easier.

Example:

'Café périferôl'.mb_chars.split(%ré/).map { |part| part.upcase.to_s } # => ["CAF", " P", "RIFERÔL"]
# File activesupport/lib/active_support/multibyte/chars.rb, line 248
def split(*args)
  @wrapped_string.split(*args).map { |i| i.mb_chars }
end
strip()

Strips entire range of Unicode whitespace from the right and left of the string.

# File activesupport/lib/active_support/multibyte/chars.rb, line 186
def strip
  rstrip.lstrip
end
tidy_bytes(force = false)

Replaces all ISO-8859-1 or CP1252 characters by their UTF-8 equivalent resulting in a valid UTF-8 string.

Passing true will forcibly tidy all bytes, assuming that the string’s encoding is entirely CP1252 or ISO-8859-1.

# File activesupport/lib/active_support/multibyte/chars.rb, line 412
def tidy_bytes(force = false)
  chars(Unicode.tidy_bytes(@wrapped_string, force))
end
titlecase()
titleize()

Capitalizes the first letter of every word, when possible.

Example:

"ÉL QUE SE ENTERÓ".mb_chars.titleize    # => "Él Que Se Enteró"
"日本語".mb_chars.titleize                 # => "日本語"
Also aliased as: titlecase
# File activesupport/lib/active_support/multibyte/chars.rb, line 367
def titleize
  chars(downcase.to_s.gsub(%r\b('?[\S])/) { Unicode.apply_mapping $1, :uppercase_mapping })
end
upcase()

Convert characters in the string to uppercase.

Example:

'Laurent, où sont les tests ?'.mb_chars.upcase.to_s # => "LAURENT, OÙ SONT LES TESTS ?"
# File activesupport/lib/active_support/multibyte/chars.rb, line 342
def upcase
  chars(Unicode.apply_mapping @wrapped_string, :uppercase_mapping)
end