# <!-- rdoc-file=string.c -->
# A String object has an arbitrary sequence of bytes, typically representing
# text or binary data. A String object may be created using String::new or as
# literals.
#
# String objects differ from Symbol objects in that Symbol objects are designed
# to be used as identifiers, instead of text or data.
#
# You can create a String object explicitly with:
#
# *   A [string literal](doc/syntax/literals_rdoc.html#label-String+Literals).
# *   A [heredoc
#     literal](doc/syntax/literals_rdoc.html#label-Here+Document+Literals).
#
#
# You can convert certain objects to Strings with:
#
# *   Method [String](Kernel.html#method-i-String).
#
#
# Some String methods modify `self`. Typically, a method whose name ends with
# `!` modifies `self` and returns `self`; often a similarly named method
# (without the `!`) returns a new string.
#
# In general, if there exist both bang and non-bang version of method, the bang!
# mutates and the non-bang! does not. However, a method without a bang can also
# mutate, such as String#replace.
#
# ## Substitution Methods
#
# These methods perform substitutions:
#
# *   String#sub: One substitution (or none); returns a new string.
# *   String#sub!: One substitution (or none); returns `self`.
# *   String#gsub: Zero or more substitutions; returns a new string.
# *   String#gsub!: Zero or more substitutions; returns `self`.
#
#
# Each of these methods takes:
#
# *   A first argument, `pattern` (string or regexp), that specifies the
#     substring(s) to be replaced.
#
# *   Either of these:
#
#     *   A second argument, `replacement` (string or hash), that determines the
#         replacing string.
#     *   A block that will determine the replacing string.
#
#
#
# The examples in this section mostly use methods String#sub and String#gsub;
# the principles illustrated apply to all four substitution methods.
#
# **Argument `pattern`**
#
# Argument `pattern` is commonly a regular expression:
#
#     s = 'hello'
#     s.sub(/[aeiou]/, '*')  # => "h*llo"
#     s.gsub(/[aeiou]/, '*') # => "h*ll*"
#     s.gsub(/[aeiou]/, '')  # => "hll"
#     s.sub(/ell/, 'al')     # => "halo"
#     s.gsub(/xyzzy/, '*')   # => "hello"
#     'THX1138'.gsub(/\d+/, '00') # => "THX00"
#
# When `pattern` is a string, all its characters are treated as ordinary
# characters (not as regexp special characters):
#
#     'THX1138'.gsub('\d+', '00') # => "THX1138"
#
# **\String `replacement`**
#
# If `replacement` is a string, that string will determine the replacing string
# that is to be substituted for the matched text.
#
# Each of the examples above uses a simple string as the replacing string.
#
# String `replacement` may contain back-references to the pattern's captures:
#
# *   `\n` (*n* a non-negative integer) refers to `$n`.
# *   `\k<name>` refers to the named capture `name`.
#
#
# See regexp.rdoc for details.
#
# Note that within the string `replacement`, a character combination such as
# `$&` is treated as ordinary text, and not as a special match variable.
# However, you may refer to some special match variables using these
# combinations:
#
# *   `\&` and `\0` correspond to `$&`, which contains the complete matched
#     text.
# *   `\'` corresponds to `$'`, which contains string after match.
# *   `\`` corresponds to `$``, which contains string before match.
# *   `+` corresponds to `$+`, which contains last capture group.
#
#
# See regexp.rdoc for details.
#
# Note that `\\\` is interpreted as an escape, i.e., a single backslash.
#
# Note also that a string literal consumes backslashes. See [String
# Literals](doc/syntax/literals_rdoc.html#label-String+Literals) for details
# about string literals.
#
# A back-reference is typically preceded by an additional backslash. For
# example, if you want to write a back-reference `\&` in `replacement` with a
# double-quoted string literal, you need to write `"..\\\\&.."`.
#
# If you want to write a non-back-reference string `\&` in `replacement`, you
# need first to escape the backslash to prevent this method from interpreting it
# as a back-reference, and then you need to escape the backslashes again to
# prevent a string literal from consuming them: `"..\\\\\\\\&.."`.
#
# You may want to use the block form to avoid a lot of backslashes.
#
# **\Hash `replacement`**
#
# If argument `replacement` is a hash, and `pattern` matches one of its keys,
# the replacing string is the value for that key:
#
#     h = {'foo' => 'bar', 'baz' => 'bat'}
#     'food'.sub('foo', h) # => "bard"
#
# Note that a symbol key does not match:
#
#     h = {foo: 'bar', baz: 'bat'}
#     'food'.sub('foo', h) # => "d"
#
# **Block**
#
# In the block form, the current match string is passed to the block; the
# block's return value becomes the replacing string:
#
#      s = '@'
#     '1234'.gsub(/\d/) {|match| s.succ! } # => "ABCD"
#
# Special match variables such as `$1`, `$2`, `$``, `$&`, and `$'` are set
# appropriately.
#
# ## What's Here
#
# First, what's elsewhere. Class String:
#
# *   Inherits from [class
#     Object](Object.html#class-Object-label-What-27s+Here).
# *   Includes [module
#     Comparable](Comparable.html#module-Comparable-label-What-27s+Here).
#
#
# Here, class String provides methods that are useful for:
#
# *   [Creating a String](#class-String-label-Methods+for+Creating+a+String)
# *   [Frozen/Unfrozen
#     Strings](#class-String-label-Methods+for+a+Frozen-2FUnfrozen+String)
# *   [Querying](#class-String-label-Methods+for+Querying)
# *   [Comparing](#class-String-label-Methods+for+Comparing)
# *   [Modifying a String](#class-String-label-Methods+for+Modifying+a+String)
# *   [Converting to New
#     String](#class-String-label-Methods+for+Converting+to+New+String)
# *   [Converting to
#     Non-String](#class-String-label-Methods+for+Converting+to+Non--5CString)
# *   [Iterating](#class-String-label-Methods+for+Iterating)
#
#
# ### Methods for Creating a String
#
#     ::new
# :       Returns a new string.
#
#     ::try_convert
# :       Returns a new string created from a given object.
#
#
#
# ### Methods for a Frozen/Unfrozen String
#
#     [#+string](#method-i-2B-40)
# :       Returns a string that is not frozen: `self`, if not frozen; `self.dup`
#         otherwise.
#
#     [#-string](#method-i-2D-40)
# :       Returns a string that is frozen: `self`, if already frozen;
#         `self.freeze` otherwise.
#
#     #freeze
# :       Freezes `self`, if not already frozen; returns `self`.
#
#
#
# ### Methods for Querying
#
# *Counts*
#
#     #length, #size
# :       Returns the count of characters (not bytes).
#
#     #empty?
# :       Returns `true` if `self.length` is zero; `false` otherwise.
#
#     #bytesize
# :       Returns the count of bytes.
#
#     #count
# :       Returns the count of substrings matching given strings.
#
#
#
# *Substrings*
#
#     [#=~](#method-i-3D~)
# :       Returns the index of the first substring that matches a given Regexp
#         or other object; returns `nil` if no match is found.
#
#     #index
# :       Returns the index of the *first* occurrence of a given substring;
#         returns `nil` if none found.
#
#     #rindex
# :       Returns the index of the *last* occurrence of a given substring;
#         returns `nil` if none found.
#
#     #include?
# :       Returns `true` if the string contains a given substring; `false`
#         otherwise.
#
#     #match
# :       Returns a MatchData object if the string matches a given Regexp; `nil`
#         otherwise.
#
#     #match?
# :       Returns `true` if the string matches a given Regexp; `false`
#         otherwise.
#
#     #start_with?
# :       Returns `true` if the string begins with any of the given substrings.
#
#     #end_with?
# :       Returns `true` if the string ends with any of the given substrings.
#
#
#
# *Encodings*
#
#     #encoding
# :       Returns the Encoding object that represents the encoding of the
#         string.
#
#     #unicode_normalized?
# :       Returns `true` if the string is in Unicode normalized form; `false`
#         otherwise.
#
#     #valid_encoding?
# :       Returns `true` if the string contains only characters that are valid
#         for its encoding.
#
#     #ascii_only?
# :       Returns `true` if the string has only ASCII characters; `false`
#         otherwise.
#
#
#
# *Other*
#
#     #sum
# :       Returns a basic checksum for the string: the sum of each byte.
#
#     #hash
# :       Returns the integer hash code.
#
#
#
# ### Methods for Comparing
#
#     [#==, #===](#method-i-3D-3D)
# :       Returns `true` if a given other string has the same content as `self`.
#
#     #eql?
# :       Returns `true` if the content is the same as the given other string.
#
#     [#<=>](#method-i-3C-3D-3E)
# :       Returns -1, 0, or 1 as a given other string is smaller than, equal to,
#         or larger than `self`.
#
#     #casecmp
# :       Ignoring case, returns -1, 0, or 1 as a given other string is smaller
#         than, equal to, or larger than `self`.
#
#     #casecmp?
# :       Returns `true` if the string is equal to a given string after Unicode
#         case folding; `false` otherwise.
#
#
#
# ### Methods for Modifying a String
#
# Each of these methods modifies `self`.
#
# *Insertion*
#
#     #insert
# :       Returns `self` with a given string inserted at a given offset.
#
#     #<<
# :       Returns `self` concatenated with a given string or integer.
#
#
#
# *Substitution*
#
#     #sub!
# :       Replaces the first substring that matches a given pattern with a given
#         replacement string; returns `self` if any changes, `nil` otherwise.
#
#     #gsub!
# :       Replaces each substring that matches a given pattern with a given
#         replacement string; returns `self` if any changes, `nil` otherwise.
#
#     #succ!, #next!
# :       Returns `self` modified to become its own successor.
#
#     #replace
# :       Returns `self` with its entire content replaced by a given string.
#
#     #reverse!
# :       Returns `self` with its characters in reverse order.
#
#     #setbyte
# :       Sets the byte at a given integer offset to a given value; returns the
#         argument.
#
#     #tr!
# :       Replaces specified characters in `self` with specified replacement
#         characters; returns `self` if any changes, `nil` otherwise.
#
#     #tr_s!
# :       Replaces specified characters in `self` with specified replacement
#         characters, removing duplicates from the substrings that were
#         modified; returns `self` if any changes, `nil` otherwise.
#
#
#
# *Casing*
#
#     #capitalize!
# :       Upcases the initial character and downcases all others; returns `self`
#         if any changes, `nil` otherwise.
#
#     #downcase!
# :       Downcases all characters; returns `self` if any changes, `nil`
#         otherwise.
#
#     #upcase!
# :       Upcases all characters; returns `self` if any changes, `nil`
#         otherwise.
#
#     #swapcase!
# :       Upcases each downcase character and downcases each upcase character;
#         returns `self` if any changes, `nil` otherwise.
#
#
#
# *Encoding*
#
#     #encode!
# :       Returns `self` with all characters transcoded from one given encoding
#         into another.
#
#     #unicode_normalize!
# :       Unicode-normalizes `self`; returns `self`.
#
#     #scrub!
# :       Replaces each invalid byte with a given character; returns `self`.
#
#     #force_encoding
# :       Changes the encoding to a given encoding; returns `self`.
#
#
#
# *Deletion*
#
#     #clear
# :       Removes all content, so that `self` is empty; returns `self`.
#
#     #slice!, #[]=
# :       Removes a substring determined by a given index, start/length, range,
#         regexp, or substring.
#
#     #squeeze!
# :       Removes contiguous duplicate characters; returns `self`.
#
#     #delete!
# :       Removes characters as determined by the intersection of substring
#         arguments.
#
#     #lstrip!
# :       Removes leading whitespace; returns `self` if any changes, `nil`
#         otherwise.
#
#     #rstrip!
# :       Removes trailing whitespace; returns `self` if any changes, `nil`
#         otherwise.
#
#     #strip!
# :       Removes leading and trailing whitespace; returns `self` if any
#         changes, `nil` otherwise.
#
#     #chomp!
# :       Removes trailing record separator, if found; returns `self` if any
#         changes, `nil` otherwise.
#
#     #chop!
# :       Removes trailing whitespace if found, otherwise removes the last
#         character; returns `self` if any changes, `nil` otherwise.
#
#
#
# ### Methods for Converting to New String
#
# Each of these methods returns a new String based on `self`, often just a
# modified copy of `self`.
#
# *Extension*
#
#     #*
# :       Returns the concatenation of multiple copies of `self`,
#
#     #+
# :       Returns the concatenation of `self` and a given other string.
#
#     #center
# :       Returns a copy of `self` centered between pad substring.
#
#     #concat
# :       Returns the concatenation of `self` with given other strings.
#
#     #prepend
# :       Returns the concatenation of a given other string with `self`.
#
#     #ljust
# :       Returns a copy of `self` of a given length, right-padded with a given
#         other string.
#
#     #rjust
# :       Returns a copy of `self` of a given length, left-padded with a given
#         other string.
#
#
#
# *Encoding*
#
#     #b
# :       Returns a copy of `self` with ASCII-8BIT encoding.
#
#     #scrub
# :       Returns a copy of `self` with each invalid byte replaced with a given
#         character.
#
#     #unicode_normalize
# :       Returns a copy of `self` with each character Unicode-normalized.
#
#     #encode
# :       Returns a copy of `self` with all characters transcoded from one given
#         encoding into another.
#
#
#
# *Substitution*
#
#     #dump
# :       Returns a copy of +self with all non-printing characters replaced by
#         xHH notation and all special characters escaped.
#
#     #undump
# :       Returns a copy of +self with all `\xNN` notation replace by `\uNNNN`
#         notation and all escaped characters unescaped.
#
#     #sub
# :       Returns a copy of `self` with the first substring matching a given
#         pattern replaced with a given replacement string;.
#
#     #gsub
# :       Returns a copy of `self` with each substring that matches a given
#         pattern replaced with a given replacement string.
#
#     #succ, #next
# :       Returns the string that is the successor to `self`.
#
#     #reverse
# :       Returns a copy of `self` with its characters in reverse order.
#
#     #tr
# :       Returns a copy of `self` with specified characters replaced with
#         specified replacement characters.
#
#     #tr_s
# :       Returns a copy of `self` with specified characters replaced with
#         specified replacement characters, removing duplicates from the
#         substrings that were modified.
#
#     #%
# :       Returns the string resulting from formatting a given object into
#         `self`
#
#
#
# *Casing*
#
#     #capitalize
# :       Returns a copy of `self` with the first character upcased and all
#         other characters downcased.
#
#     #downcase
# :       Returns a copy of `self` with all characters downcased.
#
#     #upcase
# :       Returns a copy of `self` with all characters upcased.
#
#     #swapcase
# :       Returns a copy of `self` with all upcase characters downcased and all
#         downcase characters upcased.
#
#
#
# *Deletion*
#
#     #delete
# :       Returns a copy of `self` with characters removed
#
#     #delete_prefix
# :       Returns a copy of `self` with a given prefix removed.
#
#     #delete_suffix
# :       Returns a copy of `self` with a given suffix removed.
#
#     #lstrip
# :       Returns a copy of `self` with leading whitespace removed.
#
#     #rstrip
# :       Returns a copy of `self` with trailing whitespace removed.
#
#     #strip
# :       Returns a copy of `self` with leading and trailing whitespace removed.
#
#     #chomp
# :       Returns a copy of `self` with a trailing record separator removed, if
#         found.
#
#     #chop
# :       Returns a copy of `self` with trailing whitespace or the last
#         character removed.
#
#     #squeeze
# :       Returns a copy of `self` with contiguous duplicate characters removed.
#
#     #[], #slice
# :       Returns a substring determined by a given index, start/length, or
#         range, or string.
#
#     #byteslice
# :       Returns a substring determined by a given index, start/length, or
#         range.
#
#     #chr
# :       Returns the first character.
#
#
#
# *Duplication*
#
#     #to_s, $to_str
# :       If `self` is a subclass of String, returns `self` copied into a
#         String; otherwise, returns `self`.
#
#
#
# ### Methods for Converting to Non-String
#
# Each of these methods converts the contents of `self` to a non-String.
#
# *Characters, Bytes, and Clusters*
#
#     #bytes
# :       Returns an array of the bytes in `self`.
#
#     #chars
# :       Returns an array of the characters in `self`.
#
#     #codepoints
# :       Returns an array of the integer ordinals in `self`.
#
#     #getbyte
# :       Returns an integer byte as determined by a given index.
#
#     #grapheme_clusters
# :       Returns an array of the grapheme clusters in `self`.
#
#
#
# *Splitting*
#
#     #lines
# :       Returns an array of the lines in `self`, as determined by a given
#         record separator.
#
#     #partition
# :       Returns a 3-element array determined by the first substring that
#         matches a given substring or regexp,
#
#     #rpartition
# :       Returns a 3-element array determined by the last substring that
#         matches a given substring or regexp,
#
#     #split
# :       Returns an array of substrings determined by a given delimiter --
#         regexp or string -- or, if a block given, passes those substrings to
#         the block.
#
#
#
# *Matching*
#
#     #scan
# :       Returns an array of substrings matching a given regexp or string, or,
#         if a block given, passes each matching substring to the  block.
#
#     #unpack
# :       Returns an array of substrings extracted from `self` according to a
#         given format.
#
#     #unpack1
# :       Returns the first substring extracted from `self` according to a given
#         format.
#
#
#
# *Numerics*
#
#     #hex
# :       Returns the integer value of the leading characters, interpreted as
#         hexadecimal digits.
#
#     #oct
# :       Returns the integer value of the leading characters, interpreted as
#         octal digits.
#
#     #ord
# :       Returns the integer ordinal of the first character in `self`.
#
#     #to_i
# :       Returns the integer value of leading characters, interpreted as an
#         integer.
#
#     #to_f
# :       Returns the floating-point value of leading characters, interpreted as
#         a floating-point number.
#
#
#
# *Strings and Symbols*
#
#     #inspect
# :       Returns copy of `self`, enclosed in double-quotes, with special
#         characters escaped.
#
#     #to_sym, #intern
# :       Returns the symbol corresponding to `self`.
#
#
#
# ### Methods for Iterating
#
#     #each_byte
# :       Calls the given block with each successive byte in `self`.
#
#     #each_char
# :       Calls the given block with each successive character in `self`.
#
#     #each_codepoint
# :       Calls the given block with each successive integer codepoint in
#         `self`.
#
#     #each_grapheme_cluster
# :       Calls the given block with each successive grapheme cluster in `self`.
#
#     #each_line
# :       Calls the given block with each successive line in `self`, as
#         determined by a given record separator.
#
#     #upto
# :       Calls the given block with each string value returned by successive
#         calls to #succ.
#
class String
  include Comparable

  # <!--
  #   rdoc-file=string.c
  #   - String.try_convert(object) -> object, new_string, or nil
  # -->
  # If `object` is a String object, returns `object`.
  #
  # Otherwise if `object` responds to `:to_str`, calls `object.to_str` and returns
  # the result.
  #
  # Returns `nil` if `object` does not respond to `:to_str`.
  #
  # Raises an exception unless `object.to_str` returns a String object.
  #
  def self.try_convert: (untyped obj) -> String?

  public

  # <!--
  #   rdoc-file=string.c
  #   - string % object -> new_string
  # -->
  # Returns the result of formatting `object` into the format specification `self`
  # (see Kernel#sprintf for formatting details):
  #
  #     "%05d" % 123 # => "00123"
  #
  # If `self` contains multiple substitutions, `object` must be an Array or Hash
  # containing the values to be substituted:
  #
  #     "%-5s: %016x" % [ "ID", self.object_id ] # => "ID   : 00002b054ec93168"
  #     "foo = %{foo}" % {foo: 'bar'} # => "foo = bar"
  #     "foo = %{foo}, baz = %{baz}" % {foo: 'bar', baz: 'bat'} # => "foo = bar, baz = bat"
  #
  def %: (Hash[Symbol, untyped]) -> String
       | (Array[untyped]) -> String
       | (untyped arg) -> String

  # <!--
  #   rdoc-file=string.c
  #   - string * integer -> new_string
  # -->
  # Returns a new String containing `integer` copies of `self`:
  #
  #     "Ho! " * 3 # => "Ho! Ho! Ho! "
  #     "Ho! " * 0 # => ""
  #
  def *: (int n) -> String

  # <!--
  #   rdoc-file=string.c
  #   - string + other_string -> new_string
  # -->
  # Returns a new String containing `other_string` concatenated to `self`:
  #
  #     "Hello from " + self.to_s # => "Hello from main"
  #
  def +: (string other_str) -> String

  # <!--
  #   rdoc-file=string.c
  #   - +string -> new_string or self
  # -->
  # Returns `self` if `self` is not frozen.
  #
  # Otherwise. returns `self.dup`, which is not frozen.
  #
  def +@: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - -string -> frozen_string
  # -->
  # Returns a frozen, possibly pre-existing copy of the string.
  #
  # The returned String will be deduplicated as long as it does not have any
  # instance variables set on it.
  #
  def -@: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - string << object -> string
  # -->
  # Concatenates `object` to `self` and returns `self`:
  #
  #     s = 'foo'
  #     s << 'bar' # => "foobar"
  #     s          # => "foobar"
  #
  # If `object` is an Integer, the value is considered a codepoint and converted
  # to a character before concatenation:
  #
  #     s = 'foo'
  #     s << 33 # => "foo!"
  #
  # Related: String#concat, which takes multiple arguments.
  #
  def <<: (string | Integer str_or_codepoint) -> String

  # <!--
  #   rdoc-file=string.c
  #   - string <=> other_string -> -1, 0, 1, or nil
  # -->
  # Compares `self` and `other_string`, returning:
  #
  # *   -1 if `other_string` is larger.
  # *   0 if the two are equal.
  # *   1 if `other_string` is smaller.
  # *   `nil` if the two are incomparable.
  #
  #
  # Examples:
  #
  #     'foo' <=> 'foo' # => 0
  #     'foo' <=> 'food' # => -1
  #     'food' <=> 'foo' # => 1
  #     'FOO' <=> 'foo' # => -1
  #     'foo' <=> 'FOO' # => 1
  #     'foo' <=> 1 # => nil
  #
  def <=>: (string other) -> Integer
         | (untyped other) -> Integer?

  # <!--
  #   rdoc-file=string.c
  #   - string == object -> true or false
  #   - string === object -> true or false
  # -->
  # Returns `true` if `object` has the same length and content; as `self`; `false`
  # otherwise:
  #
  #     s = 'foo'
  #     s == 'foo' # => true
  #     s == 'food' # => false
  #     s == 'FOO' # => false
  #
  # Returns `false` if the two strings' encodings are not compatible:
  #     "\u{e4 f6 fc}".encode("ISO-8859-1") == ("\u{c4 d6 dc}") # => false
  #
  # If `object` is not an instance of String but responds to `to_str`, then the
  # two strings are compared using `object.==`.
  #
  def ==: (untyped obj) -> bool

  # <!-- rdoc-file=string.c -->
  # Returns `true` if `object` has the same length and content; as `self`; `false`
  # otherwise:
  #
  #     s = 'foo'
  #     s == 'foo' # => true
  #     s == 'food' # => false
  #     s == 'FOO' # => false
  #
  # Returns `false` if the two strings' encodings are not compatible:
  #     "\u{e4 f6 fc}".encode("ISO-8859-1") == ("\u{c4 d6 dc}") # => false
  #
  # If `object` is not an instance of String but responds to `to_str`, then the
  # two strings are compared using `object.==`.
  #
  def ===: (untyped obj) -> bool

  # <!--
  #   rdoc-file=string.c
  #   - string =~ regexp -> integer or nil
  #   - string =~ object -> integer or nil
  # -->
  # Returns the Integer index of the first substring that matches the given
  # `regexp`, or `nil` if no match found:
  #
  #     'foo' =~ /f/ # => 0
  #     'foo' =~ /o/ # => 1
  #     'foo' =~ /x/ # => nil
  #
  # Note: also updates [Regexp-related global
  # variables](Regexp.html#class-Regexp-label-Special+global+variables).
  #
  # If the given `object` is not a Regexp, returns the value returned by `object
  # =~ self`.
  #
  # Note that `string =~ regexp` is different from `regexp =~ string` (see
  # [Regexp#=~](https://ruby-doc.org/core-2.7.1/Regexp.html#method-i-3D-7E)):
  #
  #     number= nil
  #     "no. 9" =~ /(?<number>\d+)/
  #     number # => nil (not assigned)
  #     /(?<number>\d+)/ =~ "no. 9"
  #     number #=> "9"
  #
  def =~: (untyped obj) -> Integer?

  # <!--
  #   rdoc-file=string.c
  #   - string[index] -> new_string or nil
  #   - string[start, length] -> new_string or nil
  #   - string[range] -> new_string or nil
  #   - string[regexp, capture = 0] -> new_string or nil
  #   - string[substring] -> new_string or nil
  # -->
  # Returns the substring of `self` specified by the arguments.
  #
  # When the single Integer argument `index` is given, returns the 1-character
  # substring found in `self` at offset `index`:
  #
  #     'bar'[2] # => "r"
  #
  # Counts backward from the end of `self` if `index` is negative:
  #
  #     'foo'[-3] # => "f"
  #
  # Returns `nil` if `index` is out of range:
  #
  #     'foo'[3] # => nil
  #     'foo'[-4] # => nil
  #
  # When the two Integer arguments  `start` and `length` are given, returns the
  # substring of the given `length` found in `self` at offset `start`:
  #
  #     'foo'[0, 2] # => "fo"
  #     'foo'[0, 0] # => ""
  #
  # Counts backward from the end of `self` if `start` is negative:
  #
  #     'foo'[-2, 2] # => "oo"
  #
  # Special case: returns a new empty String if `start` is equal to the length of
  # `self`:
  #
  #     'foo'[3, 2] # => ""
  #
  # Returns `nil` if `start` is out of range:
  #
  #     'foo'[4, 2] # => nil
  #     'foo'[-4, 2] # => nil
  #
  # Returns the trailing substring of `self` if `length` is large:
  #
  #     'foo'[1, 50] # => "oo"
  #
  # Returns `nil` if `length` is negative:
  #
  #     'foo'[0, -1] # => nil
  #
  # When the single Range argument `range` is given, derives `start` and `length`
  # values from the given `range`, and returns values as above:
  #
  # *   `'foo'[0..1]` is equivalent to `'foo'[0, 2]`.
  # *   `'foo'[0...1]` is equivalent to `'foo'[0, 1]`.
  #
  #
  # When the Regexp argument `regexp` is given, and the `capture` argument is `0`,
  # returns the first matching substring found in `self`, or `nil` if none found:
  #
  #     'foo'[/o/] # => "o"
  #     'foo'[/x/] # => nil
  #     s = 'hello there'
  #     s[/[aeiou](.)\1/] # => "ell"
  #     s[/[aeiou](.)\1/, 0] # => "ell"
  #
  # If argument `capture` is given and not `0`, it should be either an Integer
  # capture group index or a String or Symbol capture group name; the method call
  # returns only the specified capture (see [Regexp
  # Capturing](Regexp.html#class-Regexp-label-Capturing)):
  #
  #     s = 'hello there'
  #     s[/[aeiou](.)\1/, 1] # => "l"
  #     s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, "non_vowel"] # => "l"
  #     s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, :vowel] # => "e"
  #
  # If an invalid capture group index is given, `nil` is returned.  If an invalid
  # capture group name is given, `IndexError` is raised.
  #
  # When the single String argument `substring` is given, returns the substring
  # from `self` if found, otherwise `nil`:
  #
  #     'foo'['oo'] # => "oo"
  #     'foo'['xx'] # => nil
  #
  # String#slice is an alias for String#[].
  #
  def []: (int index) -> String?
        | (int start, int length) -> String?
        | (Range[Integer] | Range[Integer?] range) -> String?
        | (Regexp regexp) -> String?
        | (Regexp regexp, int | String capture) -> String?
        | (String match_str) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - str[integer] = new_str
  #   - str[integer, integer] = new_str
  #   - str[range] = aString
  #   - str[regexp] = new_str
  #   - str[regexp, integer] = new_str
  #   - str[regexp, name] = new_str
  #   - str[other_str] = new_str
  # -->
  # Element Assignment---Replaces some or all of the content of *str*. The portion
  # of the string affected is determined using the same criteria as String#[]. If
  # the replacement string is not the same length as the text it is replacing, the
  # string will be adjusted accordingly. If the regular expression or string is
  # used as the index doesn't match a position in the string, IndexError is
  # raised. If the regular expression form is used, the optional second Integer
  # allows you to specify which portion of the match to replace (effectively using
  # the MatchData indexing rules. The forms that take an Integer will raise an
  # IndexError if the value is out of range; the Range form will raise a
  # RangeError, and the Regexp and String will raise an IndexError on negative
  # match.
  #
  def []=: (int pos, String new_str) -> String
         | (int begin_pos, int end_pos, String new_str) -> String
         | (Range[Integer] | Range[Integer?] range, String new_str) -> String
         | (Regexp regexp, String new_str) -> String
         | (Regexp regexp, int capture, String new_str) -> String
         | (Regexp regexp, String name, String new_str) -> String
         | (String other_str, String new_str) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.ascii_only?  -> true or false
  # -->
  # Returns true for a string which has only ASCII characters.
  #
  #     "abc".force_encoding("UTF-8").ascii_only?          #=> true
  #     "abc\u{6666}".force_encoding("UTF-8").ascii_only?  #=> false
  #
  def ascii_only?: () -> bool

  # <!--
  #   rdoc-file=string.c
  #   - str.b   -> str
  # -->
  # Returns a copied string whose encoding is ASCII-8BIT.
  #
  def b: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.bytes    -> an_array
  # -->
  # Returns an array of bytes in *str*.  This is a shorthand for
  # `str.each_byte.to_a`.
  #
  # If a block is given, which is a deprecated form, works the same as
  # `each_byte`.
  #
  def bytes: () -> Array[Integer]
           | () { (Integer byte) -> void } -> String

  # <!--
  #   rdoc-file=string.c
  #   - bytesize -> integer
  # -->
  # Returns the count  of bytes in `self`:
  #
  #     "\x80\u3042".bytesize # => 4
  #     "hello".bytesize # => 5
  #
  # Related: String#length.
  #
  def bytesize: () -> Integer

  # <!--
  #   rdoc-file=string.c
  #   - byteslice(index, length = 1) -> string or nil
  #   - byteslice(range)             -> string or nil
  # -->
  # Returns a substring of `self`, or `nil` if the substring cannot be
  # constructed.
  #
  # With integer arguments `index` and `length` given, returns the substring
  # beginning at the given `index` of the given `length` (if possible), or `nil`
  # if `length` is negative or `index` falls outside of `self`:
  #
  #     s = '0123456789' # => "0123456789"
  #     s.byteslice(2)   # => "2"
  #     s.byteslice(200) # => nil
  #     s.byteslice(4, 3)  # => "456"
  #     s.byteslice(4, 30) # => "456789"
  #     s.byteslice(4, -1) # => nil
  #     s.byteslice(40, 2) # => nil
  #
  # In either case above, counts backwards from the end of `self` if `index` is
  # negative:
  #
  #     s = '0123456789'   # => "0123456789"
  #     s.byteslice(-4)    # => "6"
  #     s.byteslice(-4, 3) # => "678"
  #
  # With Range argument `range` given, returns `byteslice(range.begin,
  # range.size)`:
  #
  #     s = '0123456789'    # => "0123456789"
  #     s.byteslice(4..6)   # => "456"
  #     s.byteslice(-6..-4) # => "456"
  #     s.byteslice(5..2)   # => "" # range.size is zero.
  #     s.byteslice(40..42) # => nil
  #
  # In all cases, a returned string has the same encoding as `self`:
  #
  #     s.encoding              # => #<Encoding:UTF-8>
  #     s.byteslice(4).encoding # => #<Encoding:UTF-8>
  #
  def byteslice: (int start, ?int length) -> String?
               | (Range[Integer] | Range[Integer?] range) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - capitalize(*options) -> string
  # -->
  # Returns a string containing the characters in `self`; the first character is
  # upcased; the remaining characters are downcased:
  #
  #     s = 'hello World!' # => "hello World!"
  #     s.capitalize       # => "Hello world!"
  #
  # The casing may be affected by the given `options`; see [Case
  # Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#capitalize!.
  #
  def capitalize: () -> String
                | (:ascii | :lithuanian | :turkic) -> String
                | (:lithuanian, :turkic) -> String
                | (:turkic, :lithuanian) -> String

  # <!--
  #   rdoc-file=string.c
  #   - capitalize!(*options) -> self or nil
  # -->
  # Upcases the first character in `self`; downcases the remaining characters;
  # returns `self` if any changes were made, `nil` otherwise:
  #
  #     s = 'hello World!' # => "hello World!"
  #     s.capitalize!      # => "Hello world!"
  #     s                  # => "Hello world!"
  #     s.capitalize!      # => nil
  #
  # The casing may be affected by the given `options`; see [Case
  # Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#capitalize.
  #
  def capitalize!: () -> String?
                 | (:ascii | :lithuanian | :turkic) -> String?
                 | (:lithuanian, :turkic) -> String?
                 | (:turkic, :lithuanian) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - casecmp(other_string) -> -1, 0, 1, or nil
  # -->
  # Compares `self.downcase` and `other_string.downcase`; returns:
  #
  # *   -1 if `other_string.downcase` is larger.
  # *   0 if the two are equal.
  # *   1 if `other_string.downcase` is smaller.
  # *   `nil` if the two are incomparable.
  #
  #
  # Examples:
  #
  #     'foo'.casecmp('foo') # => 0
  #     'foo'.casecmp('food') # => -1
  #     'food'.casecmp('foo') # => 1
  #     'FOO'.casecmp('foo') # => 0
  #     'foo'.casecmp('FOO') # => 0
  #     'foo'.casecmp(1) # => nil
  #
  # See [Case Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#casecmp?.
  #
  def casecmp: (untyped other) -> Integer?

  # <!--
  #   rdoc-file=string.c
  #   - casecmp?(other_string) -> true, false, or nil
  # -->
  # Returns `true` if `self` and `other_string` are equal after Unicode case
  # folding, otherwise `false`:
  #
  #     'foo'.casecmp?('foo') # => true
  #     'foo'.casecmp?('food') # => false
  #     'food'.casecmp?('foo') # => false
  #     'FOO'.casecmp?('foo') # => true
  #     'foo'.casecmp?('FOO') # => true
  #
  # Returns `nil` if the two values are incomparable:
  #
  #     'foo'.casecmp?(1) # => nil
  #
  # See [Case Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#casecmp.
  #
  def casecmp?: (untyped other) -> bool?

  # <!--
  #   rdoc-file=string.c
  #   - str.center(width, padstr=' ')   -> new_str
  # -->
  # Centers `str` in `width`.  If `width` is greater than the length of `str`,
  # returns a new String of length `width` with `str` centered and padded with
  # `padstr`; otherwise, returns `str`.
  #
  #     "hello".center(4)         #=> "hello"
  #     "hello".center(20)        #=> "       hello        "
  #     "hello".center(20, '123') #=> "1231231hello12312312"
  #
  def center: (int width, ?string padstr) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.chars    -> an_array
  # -->
  # Returns an array of characters in *str*.  This is a shorthand for
  # `str.each_char.to_a`.
  #
  # If a block is given, which is a deprecated form, works the same as
  # `each_char`.
  #
  def chars: () -> Array[String]
           | () { (String char) -> void } -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.chomp(separator=$/)   -> new_str
  # -->
  # Returns a new String with the given record separator removed from the end of
  # *str* (if present). If `$/` has not been changed from the default Ruby record
  # separator, then `chomp` also removes carriage return characters (that is, it
  # will remove `\n`, `\r`, and `\r\n`). If `$/` is an empty string, it will
  # remove all trailing newlines from the string.
  #
  #     "hello".chomp                #=> "hello"
  #     "hello\n".chomp              #=> "hello"
  #     "hello\r\n".chomp            #=> "hello"
  #     "hello\n\r".chomp            #=> "hello\n"
  #     "hello\r".chomp              #=> "hello"
  #     "hello \n there".chomp       #=> "hello \n there"
  #     "hello".chomp("llo")         #=> "he"
  #     "hello\r\n\r\n".chomp('')    #=> "hello"
  #     "hello\r\n\r\r\n".chomp('')  #=> "hello\r\n\r"
  #
  def chomp: (?string separator) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.chomp!(separator=$/)   -> str or nil
  # -->
  # Modifies *str* in place as described for String#chomp, returning *str*, or
  # `nil` if no modifications were made.
  #
  def chomp!: (?string separator) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - str.chop   -> new_str
  # -->
  # Returns a new String with the last character removed.  If the string ends with
  # `\r\n`, both characters are removed. Applying `chop` to an empty string
  # returns an empty string. String#chomp is often a safer alternative, as it
  # leaves the string unchanged if it doesn't end in a record separator.
  #
  #     "string\r\n".chop   #=> "string"
  #     "string\n\r".chop   #=> "string\n"
  #     "string\n".chop     #=> "string"
  #     "string".chop       #=> "strin"
  #     "x".chop.chop       #=> ""
  #
  def chop: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.chop!   -> str or nil
  # -->
  # Processes *str* as for String#chop, returning *str*, or `nil` if *str* is the
  # empty string.  See also String#chomp!.
  #
  def chop!: () -> String?

  # <!--
  #   rdoc-file=string.c
  #   - chr -> string
  # -->
  # Returns a string containing the first character of `self`:
  #
  #     s = 'foo' # => "foo"
  #     s.chr     # => "f"
  #
  def chr: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - clear -> self
  # -->
  # Removes the contents of `self`:
  #
  #     s = 'foo' # => "foo"
  #     s.clear   # => ""
  #
  def clear: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.codepoints   -> an_array
  # -->
  # Returns an array of the Integer ordinals of the characters in *str*.  This is
  # a shorthand for `str.each_codepoint.to_a`.
  #
  # If a block is given, which is a deprecated form, works the same as
  # `each_codepoint`.
  #
  def codepoints: () -> ::Array[Integer]
                | () { (Integer codepoint) -> void } -> String

  # <!--
  #   rdoc-file=string.c
  #   - concat(*objects) -> string
  # -->
  # Concatenates each object in `objects` to `self` and returns `self`:
  #
  #     s = 'foo'
  #     s.concat('bar', 'baz') # => "foobarbaz"
  #     s                      # => "foobarbaz"
  #
  # For each given object `object` that is an Integer, the value is considered a
  # codepoint and converted to a character before concatenation:
  #
  #     s = 'foo'
  #     s.concat(32, 'bar', 32, 'baz') # => "foo bar baz"
  #
  # Related: String#<<, which takes a single argument.
  #
  def concat: (*string | Integer str_or_codepoint) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.count([other_str]+)   -> integer
  # -->
  # Each `other_str` parameter defines a set of characters to count.  The
  # intersection of these sets defines the characters to count in `str`.  Any
  # `other_str` that starts with a caret `^` is negated.  The sequence `c1-c2`
  # means all characters between c1 and c2.  The backslash character `\` can be
  # used to escape `^` or `-` and is otherwise ignored unless it appears at the
  # end of a sequence or the end of a `other_str`.
  #
  #     a = "hello world"
  #     a.count "lo"                   #=> 5
  #     a.count "lo", "o"              #=> 2
  #     a.count "hello", "^l"          #=> 4
  #     a.count "ej-m"                 #=> 4
  #
  #     "hello^world".count "\\^aeiou" #=> 4
  #     "hello-world".count "a\\-eo"   #=> 4
  #
  #     c = "hello world\\r\\n"
  #     c.count "\\"                   #=> 2
  #     c.count "\\A"                  #=> 0
  #     c.count "X-\\w"                #=> 3
  #
  def count: (string other_str, *string other_strs) -> Integer

  # <!--
  #   rdoc-file=string.c
  #   - str.crypt(salt_str)   -> new_str
  # -->
  # Returns the string generated by calling `crypt(3)` standard library function
  # with `str` and `salt_str`, in this order, as its arguments.  Please do not use
  # this method any longer.  It is legacy; provided only for backward
  # compatibility with ruby scripts in earlier days.  It is bad to use in
  # contemporary programs for several reasons:
  #
  # *   Behaviour of C's `crypt(3)` depends on the OS it is run.  The generated
  #     string lacks data portability.
  #
  # *   On some OSes such as Mac OS, `crypt(3)` never fails (i.e. silently ends up
  #     in unexpected results).
  #
  # *   On some OSes such as Mac OS, `crypt(3)` is not thread safe.
  #
  # *   So-called "traditional" usage of `crypt(3)` is very very very weak.
  #     According to its manpage, Linux's traditional `crypt(3)` output has only
  #     2**56 variations; too easy to brute force today.  And this is the default
  #     behaviour.
  #
  # *   In order to make things robust some OSes implement so-called "modular"
  #     usage. To go through, you have to do a complex build-up of the `salt_str`
  #     parameter, by hand. Failure in generation of a proper salt string tends
  #     not to yield any errors; typos in parameters are normally not detectable.
  #
  #     *   For instance, in the following example, the second invocation of
  #         String#crypt is wrong; it has a typo in "round=" (lacks "s").  However
  #         the call does not fail and something unexpected is generated.
  #
  #             "foo".crypt("$5$rounds=1000$salt$") # OK, proper usage
  #             "foo".crypt("$5$round=1000$salt$")  # Typo not detected
  #
  #
  # *   Even in the "modular" mode, some hash functions are considered archaic and
  #     no longer recommended at all; for instance module `$1$` is officially
  #     abandoned by its author: see http://phk.freebsd.dk/sagas/md5crypt_eol/ .
  #     For another instance module `$3$` is considered completely broken: see the
  #     manpage of FreeBSD.
  #
  # *   On some OS such as Mac OS, there is no modular mode. Yet, as written
  #     above, `crypt(3)` on Mac OS never fails. This means even if you build up a
  #     proper salt string it generates a traditional DES hash anyways, and there
  #     is no way for you to be aware of.
  #
  #         "foo".crypt("$5$rounds=1000$salt$") # => "$5fNPQMxC5j6."
  #
  #
  # If for some reason you cannot migrate to other secure contemporary password
  # hashing algorithms, install the string-crypt gem and `require 'string/crypt'`
  # to continue using it.
  #
  def crypt: (string salt_str) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.delete([other_str]+)   -> new_str
  # -->
  # Returns a copy of *str* with all characters in the intersection of its
  # arguments deleted. Uses the same rules for building the set of characters as
  # String#count.
  #
  #     "hello".delete "l","lo"        #=> "heo"
  #     "hello".delete "lo"            #=> "he"
  #     "hello".delete "aeiou", "^e"   #=> "hell"
  #     "hello".delete "ej-m"          #=> "ho"
  #
  def delete: (string other_str, *string other_strs) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.delete!([other_str]+)   -> str or nil
  # -->
  # Performs a `delete` operation in place, returning *str*, or `nil` if *str* was
  # not modified.
  #
  def delete!: (string other_str, *string other_strs) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - str.delete_prefix(prefix) -> new_str
  # -->
  # Returns a copy of *str* with leading `prefix` deleted.
  #
  #     "hello".delete_prefix("hel") #=> "lo"
  #     "hello".delete_prefix("llo") #=> "hello"
  #
  def delete_prefix: (string prefix) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.delete_prefix!(prefix) -> self or nil
  # -->
  # Deletes leading `prefix` from *str*, returning `nil` if no change was made.
  #
  #     "hello".delete_prefix!("hel") #=> "lo"
  #     "hello".delete_prefix!("llo") #=> nil
  #
  def delete_prefix!: (string prefix) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - str.delete_suffix(suffix) -> new_str
  # -->
  # Returns a copy of *str* with trailing `suffix` deleted.
  #
  #     "hello".delete_suffix("llo") #=> "he"
  #     "hello".delete_suffix("hel") #=> "hello"
  #
  def delete_suffix: (string suffix) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.delete_suffix!(suffix) -> self or nil
  # -->
  # Deletes trailing `suffix` from *str*, returning `nil` if no change was made.
  #
  #     "hello".delete_suffix!("llo") #=> "he"
  #     "hello".delete_suffix!("hel") #=> nil
  #
  def delete_suffix!: (string suffix) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - downcase(*options) -> string
  # -->
  # Returns a string containing the downcased characters in `self`:
  #
  #     s = 'Hello World!' # => "Hello World!"
  #     s.downcase         # => "hello world!"
  #
  # The casing may be affected by the given `options`; see [Case
  # Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#downcase!, String#upcase, String#upcase!.
  #
  def downcase: () -> String
              | (:ascii | :fold | :lithuanian | :turkic) -> String
              | (:lithuanian, :turkic) -> String
              | (:turkic, :lithuanian) -> String

  # <!--
  #   rdoc-file=string.c
  #   - downcase!(*options) -> self or nil
  # -->
  # Downcases the characters in `self`; returns `self` if any changes were made,
  # `nil` otherwise:
  #
  #     s = 'Hello World!' # => "Hello World!"
  #     s.downcase!        # => "hello world!"
  #     s                  # => "hello world!"
  #     s.downcase!        # => nil
  #
  # The casing may be affected by the given `options`; see [Case
  # Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#downcase, String#upcase, String#upcase!.
  #
  def downcase!: () -> String?
               | (:ascii | :fold | :lithuanian | :turkic) -> String?
               | (:lithuanian, :turkic) -> String?
               | (:turkic, :lithuanian) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - dump -> string
  # -->
  # Returns a printable version of `self`, enclosed in double-quotes, with special
  # characters escaped, and with non-printing characters replaced by hexadecimal
  # notation:
  #
  #     "hello \n ''".dump    # => "\"hello \\n ''\""
  #     "\f\x00\xff\\\"".dump # => "\"\\f\\x00\\xFF\\\\\\\"\""
  #
  # Related: String#undump (inverse of String#dump).
  #
  def dump: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.each_byte {|integer| block }    -> str
  #   - str.each_byte                      -> an_enumerator
  # -->
  # Passes each byte in *str* to the given block, or returns an enumerator if no
  # block is given.
  #
  #     "hello".each_byte {|c| print c, ' ' }
  #
  # *produces:*
  #
  #     104 101 108 108 111
  #
  def each_byte: () { (Integer byte) -> void } -> self
               | () -> ::Enumerator[Integer, self]

  # <!--
  #   rdoc-file=string.c
  #   - str.each_char {|cstr| block }    -> str
  #   - str.each_char                    -> an_enumerator
  # -->
  # Passes each character in *str* to the given block, or returns an enumerator if
  # no block is given.
  #
  #     "hello".each_char {|c| print c, ' ' }
  #
  # *produces:*
  #
  #     h e l l o
  #
  def each_char: () { (String char) -> void } -> self
               | () -> ::Enumerator[String, self]

  # <!--
  #   rdoc-file=string.c
  #   - str.each_codepoint {|integer| block }    -> str
  #   - str.each_codepoint                       -> an_enumerator
  # -->
  # Passes the Integer ordinal of each character in *str*, also known as a
  # *codepoint* when applied to Unicode strings to the given block.  For encodings
  # other than UTF-8/UTF-16(BE|LE)/UTF-32(BE|LE), values are directly derived from
  # the binary representation of each character.
  #
  # If no block is given, an enumerator is returned instead.
  #
  #     "hello\u0639".each_codepoint {|c| print c, ' ' }
  #
  # *produces:*
  #
  #     104 101 108 108 111 1593
  #
  def each_codepoint: () { (Integer codepoint) -> void } -> self
                    | () -> ::Enumerator[Integer, self]

  # <!--
  #   rdoc-file=string.c
  #   - str.each_grapheme_cluster {|cstr| block }    -> str
  #   - str.each_grapheme_cluster                    -> an_enumerator
  # -->
  # Passes each grapheme cluster in *str* to the given block, or returns an
  # enumerator if no block is given. Unlike String#each_char, this enumerates by
  # grapheme clusters defined by Unicode Standard Annex #29
  # http://unicode.org/reports/tr29/
  #
  #     "a\u0300".each_char.to_a.size #=> 2
  #     "a\u0300".each_grapheme_cluster.to_a.size #=> 1
  #
  def each_grapheme_cluster: () { (String grapheme) -> void } -> self
                           | () -> ::Enumerator[String, self]

  # <!--
  #   rdoc-file=string.c
  #   - str.each_line(separator=$/, chomp: false) {|substr| block } -> str
  #   - str.each_line(separator=$/, chomp: false)                   -> an_enumerator
  # -->
  # Splits *str* using the supplied parameter as the record separator (`$/` by
  # default), passing each substring in turn to the supplied block.  If a
  # zero-length record separator is supplied, the string is split into paragraphs
  # delimited by multiple successive newlines.
  #
  # If `chomp` is `true`, `separator` will be removed from the end of each line.
  #
  # If no block is given, an enumerator is returned instead.
  #
  #     "hello\nworld".each_line {|s| p s}
  #     # prints:
  #     #   "hello\n"
  #     #   "world"
  #
  #     "hello\nworld".each_line('l') {|s| p s}
  #     # prints:
  #     #   "hel"
  #     #   "l"
  #     #   "o\nworl"
  #     #   "d"
  #
  #     "hello\n\n\nworld".each_line('') {|s| p s}
  #     # prints
  #     #   "hello\n\n"
  #     #   "world"
  #
  #     "hello\nworld".each_line(chomp: true) {|s| p s}
  #     # prints:
  #     #   "hello"
  #     #   "world"
  #
  #     "hello\nworld".each_line('l', chomp: true) {|s| p s}
  #     # prints:
  #     #   "he"
  #     #   ""
  #     #   "o\nwor"
  #     #   "d"
  #
  def each_line: (?string separator, ?chomp: boolish) { (String line) -> void } -> self
               | (?string separator, ?chomp: boolish) -> Enumerator[String, self]

  # <!--
  #   rdoc-file=string.c
  #   - empty? -> true or false
  # -->
  # Returns `true` if the length of `self` is zero, `false` otherwise:
  #
  #     "hello".empty? # => false
  #     " ".empty? # => false
  #     "".empty? # => true
  #
  def empty?: () -> bool

  # <!--
  #   rdoc-file=transcode.c
  #   - str.encode(encoding, **options)   -> str
  #   - str.encode(dst_encoding, src_encoding, **options)   -> str
  #   - str.encode(**options)   -> str
  # -->
  # The first form returns a copy of `str` transcoded to encoding `encoding`. The
  # second form returns a copy of `str` transcoded from src_encoding to
  # dst_encoding. The last form returns a copy of `str` transcoded to
  # `Encoding.default_internal`.
  #
  # By default, the first and second form raise Encoding::UndefinedConversionError
  # for characters that are undefined in the destination encoding, and
  # Encoding::InvalidByteSequenceError for invalid byte sequences in the source
  # encoding. The last form by default does not raise exceptions but uses
  # replacement strings.
  #
  # The `options` keyword arguments give details for conversion. The arguments
  # are:
  #
  # :invalid
  # :   If the value is `:replace`, #encode replaces invalid byte sequences in
  #     `str` with the replacement character.  The default is to raise the
  #     Encoding::InvalidByteSequenceError exception
  # :undef
  # :   If the value is `:replace`, #encode replaces characters which are
  #     undefined in the destination encoding with the replacement character. The
  #     default is to raise the Encoding::UndefinedConversionError.
  # :replace
  # :   Sets the replacement string to the given value. The default replacement
  #     string is "uFFFD" for Unicode encoding forms, and "?" otherwise.
  # :fallback
  # :   Sets the replacement string by the given object for undefined character.
  #     The object should be a Hash, a Proc, a Method, or an object which has []
  #     method. Its key is an undefined character encoded in the source encoding
  #     of current transcoder. Its value can be any encoding until it can be
  #     converted into the destination encoding of the transcoder.
  # :xml
  # :   The value must be `:text` or `:attr`. If the value is `:text` #encode
  #     replaces undefined characters with their (upper-case hexadecimal) numeric
  #     character references. '&', '<', and '>' are converted to "&amp;", "&lt;",
  #     and "&gt;", respectively. If the value is `:attr`, #encode also quotes the
  #     replacement result (using '"'), and replaces '"' with "&quot;".
  # :cr_newline
  # :   Replaces LF ("n") with CR ("r") if value is true.
  # :crlf_newline
  # :   Replaces LF ("n") with CRLF ("r\n") if value is true.
  # :universal_newline
  # :   Replaces CRLF ("r\n") and CR ("r") with LF ("n") if value is true.
  #
  def encode: (?encoding encoding, ?encoding from_encoding, ?invalid: :replace ?, ?undef: :replace ?, ?replace: String, ?fallback: String::encode_fallback, ?xml: :text | :attr, ?universal_newline: true, ?cr_newline: true, ?crlf_newline: true) -> String

  # <!--
  #   rdoc-file=transcode.c
  #   - str.encode!(encoding, **options)   -> str
  #   - str.encode!(dst_encoding, src_encoding, **options)   -> str
  # -->
  # The first form transcodes the contents of *str* from str.encoding to
  # `encoding`. The second form transcodes the contents of *str* from src_encoding
  # to dst_encoding. The `options` keyword arguments give details for conversion.
  # See String#encode for details. Returns the string even if no changes were
  # made.
  #
  def encode!: (?encoding encoding, ?encoding from_encoding, ?invalid: :replace ?, ?undef: :replace ?, ?replace: String, ?fallback: String::encode_fallback, ?xml: :text | :attr, ?universal_newline: true, ?cr_newline: true, ?crlf_newline: true) -> self

  # <!--
  #   rdoc-file=string.c
  #   - obj.encoding   -> encoding
  # -->
  # Returns the Encoding object that represents the encoding of obj.
  #
  def encoding: () -> Encoding

  # <!--
  #   rdoc-file=string.c
  #   - str.end_with?([suffixes]+)   -> true or false
  # -->
  # Returns true if `str` ends with one of the `suffixes` given.
  #
  #     "hello".end_with?("ello")               #=> true
  #
  #     # returns true if one of the +suffixes+ matches.
  #     "hello".end_with?("heaven", "ello")     #=> true
  #     "hello".end_with?("heaven", "paradise") #=> false
  #
  def end_with?: (*string suffixes) -> bool

  # <!--
  #   rdoc-file=string.c
  #   - eql?(object) -> true or false
  # -->
  # Returns `true` if `object` has the same length and content; as `self`; `false`
  # otherwise:
  #
  #     s = 'foo'
  #     s.eql?('foo') # => true
  #     s.eql?('food') # => false
  #     s.eql?('FOO') # => false
  #
  # Returns `false` if the two strings' encodings are not compatible:
  #
  #     "\u{e4 f6 fc}".encode("ISO-8859-1").eql?("\u{c4 d6 dc}") # => false
  #
  def eql?: (untyped other) -> bool

  # <!--
  #   rdoc-file=string.c
  #   - str.force_encoding(encoding)   -> str
  # -->
  # Changes the encoding to `encoding` and returns self.
  #
  def force_encoding: (string | Encoding encoding) -> self

  # <!--
  #   rdoc-file=string.c
  #   - freeze()
  # -->
  #
  def freeze: () -> self

  # <!--
  #   rdoc-file=string.c
  #   - getbyte(index) -> integer
  # -->
  # Returns the byte at zero-based `index` as an integer:
  #
  #     s = 'abcde'  # => "abcde"
  #     s.getbyte(0) # => 97
  #     s.getbyte(1) # => 98
  #
  # Related: String#setbyte.
  #
  def getbyte: (int index) -> Integer?

  # <!--
  #   rdoc-file=string.c
  #   - str.grapheme_clusters   -> an_array
  # -->
  # Returns an array of grapheme clusters in *str*.  This is a shorthand for
  # `str.each_grapheme_cluster.to_a`.
  #
  # If a block is given, which is a deprecated form, works the same as
  # `each_grapheme_cluster`.
  #
  def grapheme_clusters: () -> ::Array[::String]

  # <!--
  #   rdoc-file=string.c
  #   - gsub(pattern, replacement)   -> new_string
  #   - gsub(pattern) {|match| ... } -> new_string
  #   - gsub(pattern)                -> enumerator
  # -->
  # Returns a copy of `self` with all occurrences of the given `pattern` replaced.
  #
  # See [Substitution Methods](#class-String-label-Substitution+Methods).
  #
  # Returns an Enumerator if no `replacement` and no block given.
  #
  # Related: String#sub, String#sub!, String#gsub!.
  #
  def gsub: (Regexp | string pattern, string replacement) -> String
          | (Regexp | string pattern, Hash[String, String] hash) -> String
          | (Regexp | string pattern) { (String match) -> _ToS } -> String
          | (Regexp | string pattern) -> ::Enumerator[String, self]

  # <!--
  #   rdoc-file=string.c
  #   - gsub!(pattern, replacement)   -> self or nil
  #   - gsub!(pattern) {|match| ... } -> self or nil
  #   - gsub!(pattern)                -> an_enumerator
  # -->
  # Performs the specified substring replacement(s) on `self`; returns `self` if
  # any replacement occurred, `nil` otherwise.
  #
  # See [Substitution Methods](#class-String-label-Substitution+Methods).
  #
  # Returns an Enumerator if no `replacement` and no block given.
  #
  # Related: String#sub, String#gsub, String#sub!.
  #
  def gsub!: (Regexp | string pattern, string replacement) -> String?
           | (Regexp | string pattern, Hash[String, String] hash) -> String?
           | (Regexp | string pattern) { (String match) -> _ToS } -> String?
           | (Regexp | string pattern) -> ::Enumerator[String, self]

  # <!--
  #   rdoc-file=string.c
  #   - hash -> integer
  # -->
  # Returns the integer hash value for `self`. The value is based on the length,
  # content and encoding of `self`.
  #
  # Related: Object#hash.
  #
  def hash: () -> Integer

  # <!--
  #   rdoc-file=string.c
  #   - str.hex   -> integer
  # -->
  # Treats leading characters from *str* as a string of hexadecimal digits (with
  # an optional sign and an optional `0x`) and returns the corresponding number.
  # Zero is returned on error.
  #
  #     "0x0a".hex     #=> 10
  #     "-1234".hex    #=> -4660
  #     "0".hex        #=> 0
  #     "wombat".hex   #=> 0
  #
  def hex: () -> Integer

  # <!--
  #   rdoc-file=string.c
  #   - include? other_string -> true or false
  # -->
  # Returns `true` if `self` contains `other_string`, `false` otherwise:
  #
  #     s = 'foo'
  #     s.include?('f')    # => true
  #     s.include?('fo')   # => true
  #     s.include?('food') # => false
  #
  def include?: (string other_str) -> bool

  # <!--
  #   rdoc-file=string.c
  #   - index(substring, offset = 0) -> integer or nil
  #   - index(regexp, offset = 0) -> integer or nil
  # -->
  # Returns the Integer index of the first occurrence of the given `substring`, or
  # `nil` if none found:
  #
  #     'foo'.index('f') # => 0
  #     'foo'.index('o') # => 1
  #     'foo'.index('oo') # => 1
  #     'foo'.index('ooo') # => nil
  #
  # Returns the Integer index of the first match for the given Regexp `regexp`, or
  # `nil` if none found:
  #
  #     'foo'.index(/f/) # => 0
  #     'foo'.index(/o/) # => 1
  #     'foo'.index(/oo/) # => 1
  #     'foo'.index(/ooo/) # => nil
  #
  # Integer argument `offset`, if given, specifies the position in the string to
  # begin the search:
  #
  #     'foo'.index('o', 1) # => 1
  #     'foo'.index('o', 2) # => 2
  #     'foo'.index('o', 3) # => nil
  #
  # If `offset` is negative, counts backward from the end of `self`:
  #
  #     'foo'.index('o', -1) # => 2
  #     'foo'.index('o', -2) # => 1
  #     'foo'.index('o', -3) # => 1
  #     'foo'.index('o', -4) # => nil
  #
  # Related: String#rindex.
  #
  def index: (Regexp | string substr_or_regexp, ?int offset) -> Integer?

  # <!--
  #   rdoc-file=string.c
  #   - insert(index, other_string) -> self
  # -->
  # Inserts the given `other_string` into `self`; returns `self`.
  #
  # If the Integer `index` is positive, inserts `other_string` at offset `index`:
  #
  #     'foo'.insert(1, 'bar') # => "fbaroo"
  #
  # If the Integer `index` is negative, counts backward from the end of `self` and
  # inserts `other_string` at offset `index+1` (that is, *after* `self[index]`):
  #
  #     'foo'.insert(-2, 'bar') # => "fobaro"
  #
  def insert: (int index, string other_str) -> String

  # <!--
  #   rdoc-file=string.c
  #   - inspect -> string
  # -->
  # Returns a printable version of `self`, enclosed in double-quotes, and with
  # special characters escaped:
  #
  #     s = "foo\tbar\tbaz\n"
  #     # => "foo\tbar\tbaz\n"
  #     s.inspect
  #     # => "\"foo\\tbar\\tbaz\\n\""
  #
  def inspect: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.intern   -> symbol
  #   - str.to_sym   -> symbol
  # -->
  # Returns the Symbol corresponding to *str*, creating the symbol if it did not
  # previously exist. See Symbol#id2name.
  #
  #     "Koala".intern         #=> :Koala
  #     s = 'cat'.to_sym       #=> :cat
  #     s == :cat              #=> true
  #     s = '@cat'.to_sym      #=> :@cat
  #     s == :@cat             #=> true
  #
  # This can also be used to create symbols that cannot be represented using the
  # `:xxx` notation.
  #
  #     'cat and dog'.to_sym   #=> :"cat and dog"
  #
  def intern: () -> Symbol

  # <!--
  #   rdoc-file=string.c
  #   - length -> integer
  # -->
  # Returns the count of characters (not bytes) in `self`:
  #
  #     "\x80\u3042".length # => 2
  #     "hello".length # => 5
  #
  # String#size is an alias for String#length.
  #
  # Related: String#bytesize.
  #
  def length: () -> Integer

  # <!--
  #   rdoc-file=string.c
  #   - str.lines(separator=$/, chomp: false)  -> an_array
  # -->
  # Returns an array of lines in *str* split using the supplied record separator
  # (`$/` by default).  This is a shorthand for `str.each_line(separator,
  # getline_args).to_a`.
  #
  # If `chomp` is `true`, `separator` will be removed from the end of each line.
  #
  #     "hello\nworld\n".lines              #=> ["hello\n", "world\n"]
  #     "hello  world".lines(' ')           #=> ["hello ", " ", "world"]
  #     "hello\nworld\n".lines(chomp: true) #=> ["hello", "world"]
  #
  # If a block is given, which is a deprecated form, works the same as
  # `each_line`.
  #
  def lines: (?string separator, ?chomp: boolish) -> Array[String]

  # <!--
  #   rdoc-file=string.c
  #   - str.ljust(integer, padstr=' ')   -> new_str
  # -->
  # If *integer* is greater than the length of *str*, returns a new String of
  # length *integer* with *str* left justified and padded with *padstr*;
  # otherwise, returns *str*.
  #
  #     "hello".ljust(4)            #=> "hello"
  #     "hello".ljust(20)           #=> "hello               "
  #     "hello".ljust(20, '1234')   #=> "hello123412341234123"
  #
  def ljust: (int integer, ?string padstr) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.lstrip   -> new_str
  # -->
  # Returns a copy of the receiver with leading whitespace removed. See also
  # String#rstrip and String#strip.
  #
  # Refer to String#strip for the definition of whitespace.
  #
  #     "  hello  ".lstrip   #=> "hello  "
  #     "hello".lstrip       #=> "hello"
  #
  def lstrip: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.lstrip!   -> self or nil
  # -->
  # Removes leading whitespace from the receiver. Returns the altered receiver, or
  # `nil` if no change was made. See also String#rstrip! and String#strip!.
  #
  # Refer to String#strip for the definition of whitespace.
  #
  #     "  hello  ".lstrip!  #=> "hello  "
  #     "hello  ".lstrip!    #=> nil
  #     "hello".lstrip!      #=> nil
  #
  def lstrip!: () -> self?

  # <!--
  #   rdoc-file=string.c
  #   - match(pattern, offset = 0) -> matchdata or nil
  #   - match(pattern, offset = 0) {|matchdata| ... } -> object
  # -->
  # Returns a Matchdata object (or `nil`) based on `self` and the given `pattern`.
  #
  # Note: also updates [Regexp-related global
  # variables](Regexp.html#class-Regexp-label-Special+global+variables).
  #
  # *   Computes `regexp` by converting `pattern` (if not already a Regexp).
  #         regexp = Regexp.new(pattern)
  #
  # *   Computes `matchdata`, which will be either a MatchData object or `nil`
  #     (see Regexp#match):
  #         matchdata = <tt>regexp.match(self)
  #
  #
  # With no block given, returns the computed `matchdata`:
  #
  #     'foo'.match('f') # => #<MatchData "f">
  #     'foo'.match('o') # => #<MatchData "o">
  #     'foo'.match('x') # => nil
  #
  # If Integer argument `offset` is given, the search begins at index `offset`:
  #
  #     'foo'.match('f', 1) # => nil
  #     'foo'.match('o', 1) # => #<MatchData "o">
  #
  # With a block given, calls the block with the computed `matchdata` and returns
  # the block's return value:
  #
  #     'foo'.match(/o/) {|matchdata| matchdata } # => #<MatchData "o">
  #     'foo'.match(/x/) {|matchdata| matchdata } # => nil
  #     'foo'.match(/f/, 1) {|matchdata| matchdata } # => nil
  #
  def match: (Regexp | string pattern, ?int pos) -> MatchData?
           | [A] (Regexp | string pattern, ?int pos) { (MatchData) -> A } -> A

  # <!--
  #   rdoc-file=string.c
  #   - match?(pattern, offset = 0) -> true or false
  # -->
  # Returns `true` or `false` based on whether a match is found for `self` and
  # `pattern`.
  #
  # Note: does not update [Regexp-related global
  # variables](Regexp.html#class-Regexp-label-Special+global+variables).
  #
  # Computes `regexp` by converting `pattern` (if not already a Regexp).
  #     regexp = Regexp.new(pattern)
  #
  # Returns `true` if `self+.match(regexp)` returns a Matchdata object, `false`
  # otherwise:
  #
  #     'foo'.match?(/o/) # => true
  #     'foo'.match?('o') # => true
  #     'foo'.match?(/x/) # => false
  #
  # If Integer argument `offset` is given, the search begins at index `offset`:
  #     'foo'.match?('f', 1) # => false
  #     'foo'.match?('o', 1) # => true
  #
  def match?: (Regexp | string pattern, ?int pos) -> bool

  # <!-- rdoc-file=string.c -->
  # Returns the successor to `self`. The successor is calculated by incrementing
  # characters.
  #
  # The first character to be incremented is the rightmost alphanumeric: or, if no
  # alphanumerics, the rightmost character:
  #
  #     'THX1138'.succ # => "THX1139"
  #     '<<koala>>'.succ # => "<<koalb>>"
  #     '***'.succ # => '**+'
  #
  # The successor to a digit is another digit, "carrying" to the next-left
  # character for a "rollover" from 9 to 0, and prepending another digit if
  # necessary:
  #
  #     '00'.succ # => "01"
  #     '09'.succ # => "10"
  #     '99'.succ # => "100"
  #
  # The successor to a letter is another letter of the same case, carrying to the
  # next-left character for a rollover, and prepending another same-case letter if
  # necessary:
  #
  #     'aa'.succ # => "ab"
  #     'az'.succ # => "ba"
  #     'zz'.succ # => "aaa"
  #     'AA'.succ # => "AB"
  #     'AZ'.succ # => "BA"
  #     'ZZ'.succ # => "AAA"
  #
  # The successor to a non-alphanumeric character is the next character in the
  # underlying character set's collating sequence, carrying to the next-left
  # character for a rollover, and prepending another character if necessary:
  #
  #     s = 0.chr * 3
  #     s # => "\x00\x00\x00"
  #     s.succ # => "\x00\x00\x01"
  #     s = 255.chr * 3
  #     s # => "\xFF\xFF\xFF"
  #     s.succ # => "\x01\x00\x00\x00"
  #
  # Carrying can occur between and among mixtures of alphanumeric characters:
  #
  #     s = 'zz99zz99'
  #     s.succ # => "aaa00aa00"
  #     s = '99zz99zz'
  #     s.succ # => "100aa00aa"
  #
  # The successor to an empty String is a new empty String:
  #
  #     ''.succ # => ""
  #
  # String#next is an alias for String#succ.
  #
  def next: () -> String

  # <!-- rdoc-file=string.c -->
  # Equivalent to String#succ, but modifies `self` in place; returns `self`.
  #
  # String#next! is an alias for String#succ!.
  #
  def next!: () -> self

  # <!--
  #   rdoc-file=string.c
  #   - str.oct   -> integer
  # -->
  # Treats leading characters of *str* as a string of octal digits (with an
  # optional sign) and returns the corresponding number.  Returns 0 if the
  # conversion fails.
  #
  #     "123".oct       #=> 83
  #     "-377".oct      #=> -255
  #     "bad".oct       #=> 0
  #     "0377bad".oct   #=> 255
  #
  # If `str` starts with `0`, radix indicators are honored. See Kernel#Integer.
  #
  def oct: () -> Integer

  # <!--
  #   rdoc-file=string.c
  #   - str.ord   -> integer
  # -->
  # Returns the Integer ordinal of a one-character string.
  #
  #     "a".ord         #=> 97
  #
  def ord: () -> Integer

  # <!--
  #   rdoc-file=string.c
  #   - str.partition(sep)              -> [head, sep, tail]
  #   - str.partition(regexp)           -> [head, match, tail]
  # -->
  # Searches *sep* or pattern (*regexp*) in the string and returns the part before
  # it, the match, and the part after it. If it is not found, returns two empty
  # strings and *str*.
  #
  #     "hello".partition("l")         #=> ["he", "l", "lo"]
  #     "hello".partition("x")         #=> ["hello", "", ""]
  #     "hello".partition(/.l/)        #=> ["h", "el", "lo"]
  #
  def partition: (Regexp | string sep_or_regexp) -> [ String, String, String ]

  # <!--
  #   rdoc-file=string.c
  #   - prepend(*other_strings)  -> string
  # -->
  # Prepends each string in `other_strings` to `self` and returns `self`:
  #
  #     s = 'foo'
  #     s.prepend('bar', 'baz') # => "barbazfoo"
  #     s                       # => "barbazfoo"
  #
  # Related: String#concat.
  #
  def prepend: (*string other_strs) -> String

  # <!-- rdoc-file=string.c -->
  # Replaces the contents of `self` with the contents of `other_string`:
  #
  #     s = 'foo'        # => "foo"
  #     s.replace('bar') # => "bar"
  #
  def replace: (string other_str) -> String

  # <!--
  #   rdoc-file=string.c
  #   - reverse -> string
  # -->
  # Returns a new string with the characters from `self` in reverse order.
  #
  #     'stressed'.reverse # => "desserts"
  #
  def reverse: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - reverse! -> self
  # -->
  # Returns `self` with its characters reversed:
  #
  #     s = 'stressed'
  #     s.reverse! # => "desserts"
  #     s          # => "desserts"
  #
  def reverse!: () -> self

  # <!--
  #   rdoc-file=string.c
  #   - rindex(substring, offset = self.length) -> integer or nil
  #   - rindex(regexp, offset = self.length) -> integer or nil
  # -->
  # Returns the Integer index of the *last* occurrence of the given `substring`,
  # or `nil` if none found:
  #
  #     'foo'.rindex('f') # => 0
  #     'foo'.rindex('o') # => 2
  #     'foo'.rindex('oo') # => 1
  #     'foo'.rindex('ooo') # => nil
  #
  # Returns the Integer index of the *last* match for the given Regexp `regexp`,
  # or `nil` if none found:
  #
  #     'foo'.rindex(/f/) # => 0
  #     'foo'.rindex(/o/) # => 2
  #     'foo'.rindex(/oo/) # => 1
  #     'foo'.rindex(/ooo/) # => nil
  #
  # The *last* match means starting at the possible last position, not the last of
  # longest matches.
  #
  #     'foo'.rindex(/o+/) # => 2
  #     $~ #=> #<MatchData "o">
  #
  # To get the last longest match, needs to combine with negative lookbehind.
  #
  #     'foo'.rindex(/(?<!o)o+/) # => 1
  #     $~ #=> #<MatchData "oo">
  #
  # Or String#index with negative lookforward.
  #
  #     'foo'.index(/o+(?!.*o)/) # => 1
  #     $~ #=> #<MatchData "oo">
  #
  # Integer argument `offset`, if given and non-negative, specifies the maximum
  # starting position in the
  #     string to _end_ the search:
  #
  #      'foo'.rindex('o', 0) # => nil
  #      'foo'.rindex('o', 1) # => 1
  #      'foo'.rindex('o', 2) # => 2
  #      'foo'.rindex('o', 3) # => 2
  #
  # If `offset` is a negative Integer, the maximum starting position in the string
  # to *end* the search is the sum of the string's length and `offset`:
  #
  #     'foo'.rindex('o', -1) # => 2
  #     'foo'.rindex('o', -2) # => 1
  #     'foo'.rindex('o', -3) # => nil
  #     'foo'.rindex('o', -4) # => nil
  #
  # Related: String#index.
  #
  def rindex: (string | Regexp substr_or_regexp, ?int pos) -> Integer?

  # <!--
  #   rdoc-file=string.c
  #   - str.rjust(integer, padstr=' ')   -> new_str
  # -->
  # If *integer* is greater than the length of *str*, returns a new String of
  # length *integer* with *str* right justified and padded with *padstr*;
  # otherwise, returns *str*.
  #
  #     "hello".rjust(4)            #=> "hello"
  #     "hello".rjust(20)           #=> "               hello"
  #     "hello".rjust(20, '1234')   #=> "123412341234123hello"
  #
  def rjust: (int integer, ?string padstr) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.rpartition(sep)             -> [head, sep, tail]
  #   - str.rpartition(regexp)          -> [head, match, tail]
  # -->
  # Searches *sep* or pattern (*regexp*) in the string from the end of the string,
  # and returns the part before it, the match, and the part after it. If it is not
  # found, returns two empty strings and *str*.
  #
  #     "hello".rpartition("l")         #=> ["hel", "l", "o"]
  #     "hello".rpartition("x")         #=> ["", "", "hello"]
  #     "hello".rpartition(/.l/)        #=> ["he", "ll", "o"]
  #
  # The match from the end means starting at the possible last position, not the
  # last of longest matches.
  #
  #     "hello".rpartition(/l+/)        #=> ["hel", "l", "o"]
  #
  # To partition at the last longest match, needs to combine with negative
  # lookbehind.
  #
  #     "hello".rpartition(/(?<!l)l+/)  #=> ["he", "ll", "o"]
  #
  # Or String#partition with negative lookforward.
  #
  #     "hello".partition(/l+(?!.*l)/)  #=> ["he", "ll", "o"]
  #
  def rpartition: (string | Regexp sep_or_regexp) -> [ String, String, String ]

  # <!--
  #   rdoc-file=string.c
  #   - str.rstrip   -> new_str
  # -->
  # Returns a copy of the receiver with trailing whitespace removed. See also
  # String#lstrip and String#strip.
  #
  # Refer to String#strip for the definition of whitespace.
  #
  #     "  hello  ".rstrip   #=> "  hello"
  #     "hello".rstrip       #=> "hello"
  #
  def rstrip: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.rstrip!   -> self or nil
  # -->
  # Removes trailing whitespace from the receiver. Returns the altered receiver,
  # or `nil` if no change was made. See also String#lstrip! and String#strip!.
  #
  # Refer to String#strip for the definition of whitespace.
  #
  #     "  hello  ".rstrip!  #=> "  hello"
  #     "  hello".rstrip!    #=> nil
  #     "hello".rstrip!      #=> nil
  #
  def rstrip!: () -> self?

  # <!--
  #   rdoc-file=string.c
  #   - str.scan(pattern)                         -> array
  #   - str.scan(pattern) {|match, ...| block }   -> str
  # -->
  # Both forms iterate through *str*, matching the pattern (which may be a Regexp
  # or a String). For each match, a result is generated and either added to the
  # result array or passed to the block. If the pattern contains no groups, each
  # individual result consists of the matched string, `$&`.  If the pattern
  # contains groups, each individual result is itself an array containing one
  # entry per group.
  #
  #     a = "cruel world"
  #     a.scan(/\w+/)        #=> ["cruel", "world"]
  #     a.scan(/.../)        #=> ["cru", "el ", "wor"]
  #     a.scan(/(...)/)      #=> [["cru"], ["el "], ["wor"]]
  #     a.scan(/(..)(..)/)   #=> [["cr", "ue"], ["l ", "wo"]]
  #
  # And the block form:
  #
  #     a.scan(/\w+/) {|w| print "<<#{w}>> " }
  #     print "\n"
  #     a.scan(/(.)(.)/) {|x,y| print y, x }
  #     print "\n"
  #
  # *produces:*
  #
  #     <<cruel>> <<world>>
  #     rceu lowlr
  #
  def scan: (Regexp | string pattern) -> Array[String | Array[String]]
          | (Regexp | string pattern) { (String | Array[String]) -> void } -> self

  # <!--
  #   rdoc-file=string.c
  #   - str.scrub -> new_str
  #   - str.scrub(repl) -> new_str
  #   - str.scrub{|bytes|} -> new_str
  # -->
  # If the string is invalid byte sequence then replace invalid bytes with given
  # replacement character, else returns self. If block is given, replace invalid
  # bytes with returned value of the block.
  #
  #     "abc\u3042\x81".scrub #=> "abc\u3042\uFFFD"
  #     "abc\u3042\x81".scrub("*") #=> "abc\u3042*"
  #     "abc\u3042\xE3\x80".scrub{|bytes| '<'+bytes.unpack1('H*')+'>' } #=> "abc\u3042<e380>"
  #
  def scrub: (?string repl) -> String
           | () { (String bytes) -> string } -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.scrub! -> str
  #   - str.scrub!(repl) -> str
  #   - str.scrub!{|bytes|} -> str
  # -->
  # If the string is invalid byte sequence then replace invalid bytes with given
  # replacement character, else returns self. If block is given, replace invalid
  # bytes with returned value of the block.
  #
  #     "abc\u3042\x81".scrub! #=> "abc\u3042\uFFFD"
  #     "abc\u3042\x81".scrub!("*") #=> "abc\u3042*"
  #     "abc\u3042\xE3\x80".scrub!{|bytes| '<'+bytes.unpack1('H*')+'>' } #=> "abc\u3042<e380>"
  #
  def scrub!: (?string repl) -> self
            | () { (String bytes) -> string } -> self

  # <!--
  #   rdoc-file=string.c
  #   - setbyte(index, integer) -> integer
  # -->
  # Sets the byte at zero-based `index` to `integer`; returns `integer`:
  #
  #     s = 'abcde'      # => "abcde"
  #     s.setbyte(0, 98) # => 98
  #     s                # => "bbcde"
  #
  # Related: String#getbyte.
  #
  def setbyte: (int index, int integer) -> int

  # <!-- rdoc-file=string.c -->
  # Returns the count of characters (not bytes) in `self`:
  #
  #     "\x80\u3042".length # => 2
  #     "hello".length # => 5
  #
  # String#size is an alias for String#length.
  #
  # Related: String#bytesize.
  #
  alias size length

  # <!-- rdoc-file=string.c -->
  # Returns the substring of `self` specified by the arguments.
  #
  # When the single Integer argument `index` is given, returns the 1-character
  # substring found in `self` at offset `index`:
  #
  #     'bar'[2] # => "r"
  #
  # Counts backward from the end of `self` if `index` is negative:
  #
  #     'foo'[-3] # => "f"
  #
  # Returns `nil` if `index` is out of range:
  #
  #     'foo'[3] # => nil
  #     'foo'[-4] # => nil
  #
  # When the two Integer arguments  `start` and `length` are given, returns the
  # substring of the given `length` found in `self` at offset `start`:
  #
  #     'foo'[0, 2] # => "fo"
  #     'foo'[0, 0] # => ""
  #
  # Counts backward from the end of `self` if `start` is negative:
  #
  #     'foo'[-2, 2] # => "oo"
  #
  # Special case: returns a new empty String if `start` is equal to the length of
  # `self`:
  #
  #     'foo'[3, 2] # => ""
  #
  # Returns `nil` if `start` is out of range:
  #
  #     'foo'[4, 2] # => nil
  #     'foo'[-4, 2] # => nil
  #
  # Returns the trailing substring of `self` if `length` is large:
  #
  #     'foo'[1, 50] # => "oo"
  #
  # Returns `nil` if `length` is negative:
  #
  #     'foo'[0, -1] # => nil
  #
  # When the single Range argument `range` is given, derives `start` and `length`
  # values from the given `range`, and returns values as above:
  #
  # *   `'foo'[0..1]` is equivalent to `'foo'[0, 2]`.
  # *   `'foo'[0...1]` is equivalent to `'foo'[0, 1]`.
  #
  #
  # When the Regexp argument `regexp` is given, and the `capture` argument is `0`,
  # returns the first matching substring found in `self`, or `nil` if none found:
  #
  #     'foo'[/o/] # => "o"
  #     'foo'[/x/] # => nil
  #     s = 'hello there'
  #     s[/[aeiou](.)\1/] # => "ell"
  #     s[/[aeiou](.)\1/, 0] # => "ell"
  #
  # If argument `capture` is given and not `0`, it should be either an Integer
  # capture group index or a String or Symbol capture group name; the method call
  # returns only the specified capture (see [Regexp
  # Capturing](Regexp.html#class-Regexp-label-Capturing)):
  #
  #     s = 'hello there'
  #     s[/[aeiou](.)\1/, 1] # => "l"
  #     s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, "non_vowel"] # => "l"
  #     s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, :vowel] # => "e"
  #
  # If an invalid capture group index is given, `nil` is returned.  If an invalid
  # capture group name is given, `IndexError` is raised.
  #
  # When the single String argument `substring` is given, returns the substring
  # from `self` if found, otherwise `nil`:
  #
  #     'foo'['oo'] # => "oo"
  #     'foo'['xx'] # => nil
  #
  # String#slice is an alias for String#[].
  #
  alias slice []

  # <!--
  #   rdoc-file=string.c
  #   - slice!(index)               -> new_string or nil
  #   - slice!(start, length)       -> new_string or nil
  #   - slice!(range)               -> new_string or nil
  #   - slice!(regexp, capture = 0) -> new_string or nil
  #   - slice!(substring)           -> new_string or nil
  # -->
  # Removes the substring of `self` specified by the arguments; returns the
  # removed substring.
  #
  # See String#[] for details about the arguments that specify the substring.
  #
  # A few examples:
  #
  #     string = "This is a string"
  #     string.slice!(2)        #=> "i"
  #     string.slice!(3..6)     #=> " is "
  #     string.slice!(/s.*t/)   #=> "sa st"
  #     string.slice!("r")      #=> "r"
  #     string                  #=> "Thing"
  #
  def slice!: (int integer, ?int integer) -> String?
            | (Range[Integer] | Range[Integer?] range) -> String?
            | (Regexp regexp, ?int | String capture) -> String?
            | (String other_str) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - str.split(pattern=nil, [limit])                -> an_array
  #   - str.split(pattern=nil, [limit]) {|sub| block } -> str
  # -->
  # Divides *str* into substrings based on a delimiter, returning an array of
  # these substrings.
  #
  # If *pattern* is a String, then its contents are used as the delimiter when
  # splitting *str*. If *pattern* is a single space, *str* is split on whitespace,
  # with leading and trailing whitespace and runs of contiguous whitespace
  # characters ignored.
  #
  # If *pattern* is a Regexp, *str* is divided where the pattern matches. Whenever
  # the pattern matches a zero-length string, *str* is split into individual
  # characters. If *pattern* contains groups, the respective matches will be
  # returned in the array as well.
  #
  # If *pattern* is `nil`, the value of `$;` is used. If `$;` is `nil` (which is
  # the default), *str* is split on whitespace as if ' ' were specified.
  #
  # If the *limit* parameter is omitted, trailing null fields are suppressed. If
  # *limit* is a positive number, at most that number of split substrings will be
  # returned (captured groups will be returned as well, but are not counted
  # towards the limit). If *limit* is `1`, the entire string is returned as the
  # only entry in an array. If negative, there is no limit to the number of fields
  # returned, and trailing null fields are not suppressed.
  #
  # When the input `str` is empty an empty Array is returned as the string is
  # considered to have no fields to split.
  #
  #     " now's  the time ".split       #=> ["now's", "the", "time"]
  #     " now's  the time ".split(' ')  #=> ["now's", "the", "time"]
  #     " now's  the time".split(/ /)   #=> ["", "now's", "", "the", "time"]
  #     "1, 2.34,56, 7".split(%r{,\s*}) #=> ["1", "2.34", "56", "7"]
  #     "hello".split(//)               #=> ["h", "e", "l", "l", "o"]
  #     "hello".split(//, 3)            #=> ["h", "e", "llo"]
  #     "hi mom".split(%r{\s*})         #=> ["h", "i", "m", "o", "m"]
  #
  #     "mellow yellow".split("ello")   #=> ["m", "w y", "w"]
  #     "1,2,,3,4,,".split(',')         #=> ["1", "2", "", "3", "4"]
  #     "1,2,,3,4,,".split(',', 4)      #=> ["1", "2", "", "3,4,,"]
  #     "1,2,,3,4,,".split(',', -4)     #=> ["1", "2", "", "3", "4", "", ""]
  #
  #     "1:2:3".split(/(:)()()/, 2)     #=> ["1", ":", "", "", "2:3"]
  #
  #     "".split(',', -1)               #=> []
  #
  # If a block is given, invoke the block with each split substring.
  #
  def split: (?Regexp | string pattern, ?int limit) -> Array[String]
           | (?Regexp | string pattern, ?int limit) { (String) -> void } -> self

  # <!--
  #   rdoc-file=string.c
  #   - str.squeeze([other_str]*)    -> new_str
  # -->
  # Builds a set of characters from the *other_str* parameter(s) using the
  # procedure described for String#count. Returns a new string where runs of the
  # same character that occur in this set are replaced by a single character. If
  # no arguments are given, all runs of identical characters are replaced by a
  # single character.
  #
  #     "yellow moon".squeeze                  #=> "yelow mon"
  #     "  now   is  the".squeeze(" ")         #=> " now is the"
  #     "putters shoot balls".squeeze("m-z")   #=> "puters shot balls"
  #
  def squeeze: (*string other_str) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.squeeze!([other_str]*)   -> str or nil
  # -->
  # Squeezes *str* in place, returning either *str*, or `nil` if no changes were
  # made.
  #
  def squeeze!: (*string other_str) -> self?

  # <!--
  #   rdoc-file=string.c
  #   - str.start_with?([prefixes]+)   -> true or false
  # -->
  # Returns true if `str` starts with one of the `prefixes` given. Each of the
  # `prefixes` should be a String or a Regexp.
  #
  #     "hello".start_with?("hell")               #=> true
  #     "hello".start_with?(/H/i)                 #=> true
  #
  #     # returns true if one of the prefixes matches.
  #     "hello".start_with?("heaven", "hell")     #=> true
  #     "hello".start_with?("heaven", "paradise") #=> false
  #
  def start_with?: (*string prefixes) -> bool

  # <!--
  #   rdoc-file=string.c
  #   - str.strip   -> new_str
  # -->
  # Returns a copy of the receiver with leading and trailing whitespace removed.
  #
  # Whitespace is defined as any of the following characters: null, horizontal
  # tab, line feed, vertical tab, form feed, carriage return, space.
  #
  #     "    hello    ".strip   #=> "hello"
  #     "\tgoodbye\r\n".strip   #=> "goodbye"
  #     "\x00\t\n\v\f\r ".strip #=> ""
  #     "hello".strip           #=> "hello"
  #
  def strip: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.strip!   -> self or nil
  # -->
  # Removes leading and trailing whitespace from the receiver. Returns the altered
  # receiver, or `nil` if there was no change.
  #
  # Refer to String#strip for the definition of whitespace.
  #
  #     "  hello  ".strip!  #=> "hello"
  #     "hello".strip!      #=> nil
  #
  def strip!: () -> self?

  # <!--
  #   rdoc-file=string.c
  #   - sub(pattern, replacement)   -> new_string
  #   - sub(pattern) {|match| ... } -> new_string
  # -->
  # Returns a copy of `self` with only the first occurrence (not all occurrences)
  # of the given `pattern` replaced.
  #
  # See [Substitution Methods](#class-String-label-Substitution+Methods).
  #
  # Related: String#sub!, String#gsub, String#gsub!.
  #
  def sub: (Regexp | string pattern, string | Hash[String, String] replacement) -> String
         | (Regexp | string pattern) { (String match) -> _ToS } -> String

  # <!--
  #   rdoc-file=string.c
  #   - sub!(pattern, replacement)   -> self or nil
  #   - sub!(pattern) {|match| ... } -> self or nil
  # -->
  # Returns `self` with only the first occurrence (not all occurrences) of the
  # given `pattern` replaced.
  #
  # See [Substitution Methods](#class-String-label-Substitution+Methods).
  #
  # Related: String#sub, String#gsub, String#gsub!.
  #
  def sub!: (Regexp | string pattern, string | Hash[String, String] replacement) -> self?
          | (Regexp | string pattern) { (String match) -> _ToS } -> String?

  # <!--
  #   rdoc-file=string.c
  #   - succ -> new_str
  # -->
  # Returns the successor to `self`. The successor is calculated by incrementing
  # characters.
  #
  # The first character to be incremented is the rightmost alphanumeric: or, if no
  # alphanumerics, the rightmost character:
  #
  #     'THX1138'.succ # => "THX1139"
  #     '<<koala>>'.succ # => "<<koalb>>"
  #     '***'.succ # => '**+'
  #
  # The successor to a digit is another digit, "carrying" to the next-left
  # character for a "rollover" from 9 to 0, and prepending another digit if
  # necessary:
  #
  #     '00'.succ # => "01"
  #     '09'.succ # => "10"
  #     '99'.succ # => "100"
  #
  # The successor to a letter is another letter of the same case, carrying to the
  # next-left character for a rollover, and prepending another same-case letter if
  # necessary:
  #
  #     'aa'.succ # => "ab"
  #     'az'.succ # => "ba"
  #     'zz'.succ # => "aaa"
  #     'AA'.succ # => "AB"
  #     'AZ'.succ # => "BA"
  #     'ZZ'.succ # => "AAA"
  #
  # The successor to a non-alphanumeric character is the next character in the
  # underlying character set's collating sequence, carrying to the next-left
  # character for a rollover, and prepending another character if necessary:
  #
  #     s = 0.chr * 3
  #     s # => "\x00\x00\x00"
  #     s.succ # => "\x00\x00\x01"
  #     s = 255.chr * 3
  #     s # => "\xFF\xFF\xFF"
  #     s.succ # => "\x01\x00\x00\x00"
  #
  # Carrying can occur between and among mixtures of alphanumeric characters:
  #
  #     s = 'zz99zz99'
  #     s.succ # => "aaa00aa00"
  #     s = '99zz99zz'
  #     s.succ # => "100aa00aa"
  #
  # The successor to an empty String is a new empty String:
  #
  #     ''.succ # => ""
  #
  # String#next is an alias for String#succ.
  #
  def succ: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - succ! -> self
  # -->
  # Equivalent to String#succ, but modifies `self` in place; returns `self`.
  #
  # String#next! is an alias for String#succ!.
  #
  def succ!: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.sum(n=16)   -> integer
  # -->
  # Returns a basic *n*-bit checksum of the characters in *str*, where *n* is the
  # optional Integer parameter, defaulting to 16. The result is simply the sum of
  # the binary value of each byte in *str* modulo `2**n - 1`. This is not a
  # particularly good checksum.
  #
  def sum: (?int n) -> Integer

  # <!--
  #   rdoc-file=string.c
  #   - swapcase(*options) -> string
  # -->
  # Returns a string containing the characters in `self`, with cases reversed;
  # each uppercase character is downcased; each lowercase character is upcased:
  #
  #     s = 'Hello World!' # => "Hello World!"
  #     s.swapcase         # => "hELLO wORLD!"
  #
  # The casing may be affected by the given `options`; see [Case
  # Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#swapcase!.
  #
  def swapcase: () -> String
              | (:ascii | :lithuanian | :turkic) -> String
              | (:lithuanian, :turkic) -> String
              | (:turkic, :lithuanian) -> String

  # <!--
  #   rdoc-file=string.c
  #   - swapcase!(*options) -> self or nil
  # -->
  # Upcases each lowercase character in `self`; downcases uppercase character;
  # returns `self` if any changes were made, `nil` otherwise:
  #
  #     s = 'Hello World!' # => "Hello World!"
  #     s.swapcase!        # => "hELLO wORLD!"
  #     s                  # => "Hello World!"
  #     ''.swapcase!       # => nil
  #
  # The casing may be affected by the given `options`; see [Case
  # Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#swapcase.
  #
  def swapcase!: () -> self?
               | (:ascii | :lithuanian | :turkic) -> self?
               | (:lithuanian, :turkic) -> self?
               | (:turkic, :lithuanian) -> self?

  # <!--
  #   rdoc-file=complex.c
  #   - str.to_c  ->  complex
  # -->
  # Returns a complex which denotes the string form.  The parser ignores leading
  # whitespaces and trailing garbage.  Any digit sequences can be separated by an
  # underscore.  Returns zero for null or garbage string.
  #
  #     '9'.to_c           #=> (9+0i)
  #     '2.5'.to_c         #=> (2.5+0i)
  #     '2.5/1'.to_c       #=> ((5/2)+0i)
  #     '-3/2'.to_c        #=> ((-3/2)+0i)
  #     '-i'.to_c          #=> (0-1i)
  #     '45i'.to_c         #=> (0+45i)
  #     '3-4i'.to_c        #=> (3-4i)
  #     '-4e2-4e-2i'.to_c  #=> (-400.0-0.04i)
  #     '-0.0-0.0i'.to_c   #=> (-0.0-0.0i)
  #     '1/2+3/4i'.to_c    #=> ((1/2)+(3/4)*i)
  #     'ruby'.to_c        #=> (0+0i)
  #
  # See Kernel.Complex.
  #
  def to_c: () -> Complex

  # <!--
  #   rdoc-file=string.c
  #   - to_f -> float
  # -->
  # Returns the result of interpreting leading characters in `self` as a Float:
  #
  #     '3.14159'.to_f  # => 3.14159
  #     '1.234e-2'.to_f # => 0.01234
  #
  # Characters past a leading valid number (in the given `base`) are ignored:
  #
  #     '3.14 (pi to two places)'.to_f # => 3.14
  #
  # Returns zero if there is no leading valid number:
  #
  #     'abcdef'.to_f # => 0.0
  #
  def to_f: () -> Float

  # <!--
  #   rdoc-file=string.c
  #   - to_i(base = 10) -> integer
  # -->
  # Returns the result of interpreting leading characters in `self` as an integer
  # in the given `base` (which must be in (2..36)):
  #
  #     '123456'.to_i     # => 123456
  #     '123def'.to_i(16) # => 1195503
  #
  # Characters past a leading valid number (in the given `base`) are ignored:
  #
  #     '12.345'.to_i   # => 12
  #     '12345'.to_i(2) # => 1
  #
  # Returns zero if there is no leading valid number:
  #
  #     'abcdef'.to_i # => 0
  #     '2'.to_i(2)   # => 0
  #
  def to_i: (?int base) -> Integer

  # <!--
  #   rdoc-file=rational.c
  #   - str.to_r  ->  rational
  # -->
  # Returns the result of interpreting leading characters in `str` as a rational.
  # Leading whitespace and extraneous characters past the end of a valid number
  # are ignored. Digit sequences can be separated by an underscore. If there is
  # not a valid number at the start of `str`, zero is returned.  This method never
  # raises an exception.
  #
  #     '  2  '.to_r       #=> (2/1)
  #     '300/2'.to_r       #=> (150/1)
  #     '-9.2'.to_r        #=> (-46/5)
  #     '-9.2e2'.to_r      #=> (-920/1)
  #     '1_234_567'.to_r   #=> (1234567/1)
  #     '21 June 09'.to_r  #=> (21/1)
  #     '21/06/09'.to_r    #=> (7/2)
  #     'BWV 1079'.to_r    #=> (0/1)
  #
  # NOTE: "0.3".to_r isn't the same as 0.3.to_r.  The former is equivalent to
  # "3/10".to_r, but the latter isn't so.
  #
  #     "0.3".to_r == 3/10r  #=> true
  #     0.3.to_r   == 3/10r  #=> false
  #
  # See also Kernel#Rational.
  #
  def to_r: () -> Rational

  # <!--
  #   rdoc-file=string.c
  #   - to_s -> self or string
  # -->
  # Returns `self` if `self` is a String, or `self` converted to a String if
  # `self` is a subclass of String.
  #
  # String#to_str is an alias for String#to_s.
  #
  def to_s: () -> String

  # <!-- rdoc-file=string.c -->
  # Returns `self` if `self` is a String, or `self` converted to a String if
  # `self` is a subclass of String.
  #
  # String#to_str is an alias for String#to_s.
  #
  def to_str: () -> String

  # <!-- rdoc-file=string.c -->
  # Returns the Symbol corresponding to *str*, creating the symbol if it did not
  # previously exist. See Symbol#id2name.
  #
  #     "Koala".intern         #=> :Koala
  #     s = 'cat'.to_sym       #=> :cat
  #     s == :cat              #=> true
  #     s = '@cat'.to_sym      #=> :@cat
  #     s == :@cat             #=> true
  #
  # This can also be used to create symbols that cannot be represented using the
  # `:xxx` notation.
  #
  #     'cat and dog'.to_sym   #=> :"cat and dog"
  #
  def to_sym: () -> Symbol

  # <!--
  #   rdoc-file=string.c
  #   - str.tr(from_str, to_str)   => new_str
  # -->
  # Returns a copy of `str` with the characters in `from_str` replaced by the
  # corresponding characters in `to_str`.  If `to_str` is shorter than `from_str`,
  # it is padded with its last character in order to maintain the correspondence.
  #
  #     "hello".tr('el', 'ip')      #=> "hippo"
  #     "hello".tr('aeiou', '*')    #=> "h*ll*"
  #     "hello".tr('aeiou', 'AA*')  #=> "hAll*"
  #
  # Both strings may use the `c1-c2` notation to denote ranges of characters, and
  # `from_str` may start with a `^`, which denotes all characters except those
  # listed.
  #
  #     "hello".tr('a-y', 'b-z')    #=> "ifmmp"
  #     "hello".tr('^aeiou', '*')   #=> "*e**o"
  #
  # The backslash character `\` can be used to escape `^` or `-` and is otherwise
  # ignored unless it appears at the end of a range or the end of the `from_str`
  # or `to_str`:
  #
  #     "hello^world".tr("\\^aeiou", "*") #=> "h*ll**w*rld"
  #     "hello-world".tr("a\\-eo", "*")   #=> "h*ll**w*rld"
  #
  #     "hello\r\nworld".tr("\r", "")   #=> "hello\nworld"
  #     "hello\r\nworld".tr("\\r", "")  #=> "hello\r\nwold"
  #     "hello\r\nworld".tr("\\\r", "") #=> "hello\nworld"
  #
  #     "X['\\b']".tr("X\\", "")   #=> "['b']"
  #     "X['\\b']".tr("X-\\]", "") #=> "'b'"
  #
  def tr: (string from_str, string to_str) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.tr!(from_str, to_str)   -> str or nil
  # -->
  # Translates *str* in place, using the same rules as String#tr. Returns *str*,
  # or `nil` if no changes were made.
  #
  def tr!: (string from_str, string to_str) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - str.tr_s(from_str, to_str)   -> new_str
  # -->
  # Processes a copy of *str* as described under String#tr, then removes duplicate
  # characters in regions that were affected by the translation.
  #
  #     "hello".tr_s('l', 'r')     #=> "hero"
  #     "hello".tr_s('el', '*')    #=> "h*o"
  #     "hello".tr_s('el', 'hx')   #=> "hhxo"
  #
  def tr_s: (string from_str, string to_str) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.tr_s!(from_str, to_str)   -> str or nil
  # -->
  # Performs String#tr_s processing on *str* in place, returning *str*, or `nil`
  # if no changes were made.
  #
  def tr_s!: (string from_str, string to_str) -> String?

  # <!--
  #   rdoc-file=string.c
  #   - undump -> string
  # -->
  # Returns an unescaped version of `self`:
  #
  #     s_orig = "\f\x00\xff\\\""    # => "\f\u0000\xFF\\\""
  #     s_dumped = s_orig.dump       # => "\"\\f\\x00\\xFF\\\\\\\"\""
  #     s_undumped = s_dumped.undump # => "\f\u0000\xFF\\\""
  #     s_undumped == s_orig         # => true
  #
  # Related: String#dump (inverse of String#undump).
  #
  def undump: () -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.unicode_normalize(form=:nfc)
  # -->
  # Unicode Normalization---Returns a normalized form of `str`, using Unicode
  # normalizations NFC, NFD, NFKC, or NFKD. The normalization form used is
  # determined by `form`, which can be any of the four values `:nfc`, `:nfd`,
  # `:nfkc`, or `:nfkd`. The default is `:nfc`.
  #
  # If the string is not in a Unicode Encoding, then an Exception is raised. In
  # this context, 'Unicode Encoding' means any of UTF-8, UTF-16BE/LE, and
  # UTF-32BE/LE, as well as GB18030, UCS_2BE, and UCS_4BE. Anything other than
  # UTF-8 is implemented by converting to UTF-8, which makes it slower than UTF-8.
  #
  #     "a\u0300".unicode_normalize        #=> "\u00E0"
  #     "a\u0300".unicode_normalize(:nfc)  #=> "\u00E0"
  #     "\u00E0".unicode_normalize(:nfd)   #=> "a\u0300"
  #     "\xE0".force_encoding('ISO-8859-1').unicode_normalize(:nfd)
  #                                        #=> Encoding::CompatibilityError raised
  #
  def unicode_normalize: (?:nfc | :nfd | :nfkc | :nfkd) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.unicode_normalize!(form=:nfc)
  # -->
  # Destructive version of String#unicode_normalize, doing Unicode normalization
  # in place.
  #
  def unicode_normalize!: (?:nfc | :nfd | :nfkc | :nfkd) -> String

  # <!--
  #   rdoc-file=string.c
  #   - str.unicode_normalized?(form=:nfc)
  # -->
  # Checks whether `str` is in Unicode normalization form `form`, which can be any
  # of the four values `:nfc`, `:nfd`, `:nfkc`, or `:nfkd`. The default is `:nfc`.
  #
  # If the string is not in a Unicode Encoding, then an Exception is raised. For
  # details, see String#unicode_normalize.
  #
  #     "a\u0300".unicode_normalized?        #=> false
  #     "a\u0300".unicode_normalized?(:nfd)  #=> true
  #     "\u00E0".unicode_normalized?         #=> true
  #     "\u00E0".unicode_normalized?(:nfd)   #=> false
  #     "\xE0".force_encoding('ISO-8859-1').unicode_normalized?
  #                                          #=> Encoding::CompatibilityError raised
  #
  def unicode_normalized?: (?:nfc | :nfd | :nfkc | :nfkd) -> bool

  # <!--
  #   rdoc-file=pack.rb
  #   - str.unpack(format)    ->  anArray
  #   - str.unpack(format, offset: anInteger)    ->  anArray
  # -->
  # Decodes *str* (which may contain binary data) according to the format string,
  # returning an array of each value extracted. The format string consists of a
  # sequence of single-character directives, summarized in the table at the end of
  # this entry. Each directive may be followed by a number, indicating the number
  # of times to repeat with this directive. An asterisk (```*`'') will use up all
  # remaining elements. The directives `sSiIlL` may each be followed by an
  # underscore (```_`'') or exclamation mark (```!`'') to use the underlying
  # platform's native size for the specified type; otherwise, it uses a
  # platform-independent consistent size. Spaces are ignored in the format string.
  #
  # See also String#unpack1,  Array#pack.
  #
  #     "abc \0\0abc \0\0".unpack('A6Z6')   #=> ["abc", "abc "]
  #     "abc \0\0".unpack('a3a3')           #=> ["abc", " \000\000"]
  #     "abc \0abc \0".unpack('Z*Z*')       #=> ["abc ", "abc "]
  #     "aa".unpack('b8B8')                 #=> ["10000110", "01100001"]
  #     "aaa".unpack('h2H2c')               #=> ["16", "61", 97]
  #     "\xfe\xff\xfe\xff".unpack('sS')     #=> [-2, 65534]
  #     "now=20is".unpack('M*')             #=> ["now is"]
  #     "whole".unpack('xax2aX2aX1aX2a')    #=> ["h", "e", "l", "l", "o"]
  #
  # This table summarizes the various formats and the Ruby classes returned by
  # each.
  #
  #     Integer       |         |
  #     Directive     | Returns | Meaning
  #     ------------------------------------------------------------------
  #     C             | Integer | 8-bit unsigned (unsigned char)
  #     S             | Integer | 16-bit unsigned, native endian (uint16_t)
  #     L             | Integer | 32-bit unsigned, native endian (uint32_t)
  #     Q             | Integer | 64-bit unsigned, native endian (uint64_t)
  #     J             | Integer | pointer width unsigned, native endian (uintptr_t)
  #                   |         |
  #     c             | Integer | 8-bit signed (signed char)
  #     s             | Integer | 16-bit signed, native endian (int16_t)
  #     l             | Integer | 32-bit signed, native endian (int32_t)
  #     q             | Integer | 64-bit signed, native endian (int64_t)
  #     j             | Integer | pointer width signed, native endian (intptr_t)
  #                   |         |
  #     S_ S!         | Integer | unsigned short, native endian
  #     I I_ I!       | Integer | unsigned int, native endian
  #     L_ L!         | Integer | unsigned long, native endian
  #     Q_ Q!         | Integer | unsigned long long, native endian (ArgumentError
  #                   |         | if the platform has no long long type.)
  #     J!            | Integer | uintptr_t, native endian (same with J)
  #                   |         |
  #     s_ s!         | Integer | signed short, native endian
  #     i i_ i!       | Integer | signed int, native endian
  #     l_ l!         | Integer | signed long, native endian
  #     q_ q!         | Integer | signed long long, native endian (ArgumentError
  #                   |         | if the platform has no long long type.)
  #     j!            | Integer | intptr_t, native endian (same with j)
  #                   |         |
  #     S> s> S!> s!> | Integer | same as the directives without ">" except
  #     L> l> L!> l!> |         | big endian
  #     I!> i!>       |         |
  #     Q> q> Q!> q!> |         | "S>" is the same as "n"
  #     J> j> J!> j!> |         | "L>" is the same as "N"
  #                   |         |
  #     S< s< S!< s!< | Integer | same as the directives without "<" except
  #     L< l< L!< l!< |         | little endian
  #     I!< i!<       |         |
  #     Q< q< Q!< q!< |         | "S<" is the same as "v"
  #     J< j< J!< j!< |         | "L<" is the same as "V"
  #                   |         |
  #     n             | Integer | 16-bit unsigned, network (big-endian) byte order
  #     N             | Integer | 32-bit unsigned, network (big-endian) byte order
  #     v             | Integer | 16-bit unsigned, VAX (little-endian) byte order
  #     V             | Integer | 32-bit unsigned, VAX (little-endian) byte order
  #                   |         |
  #     U             | Integer | UTF-8 character
  #     w             | Integer | BER-compressed integer (see Array#pack)
  #
  #     Float        |         |
  #     Directive    | Returns | Meaning
  #     -----------------------------------------------------------------
  #     D d          | Float   | double-precision, native format
  #     F f          | Float   | single-precision, native format
  #     E            | Float   | double-precision, little-endian byte order
  #     e            | Float   | single-precision, little-endian byte order
  #     G            | Float   | double-precision, network (big-endian) byte order
  #     g            | Float   | single-precision, network (big-endian) byte order
  #
  #     String       |         |
  #     Directive    | Returns | Meaning
  #     -----------------------------------------------------------------
  #     A            | String  | arbitrary binary string (remove trailing nulls and ASCII spaces)
  #     a            | String  | arbitrary binary string
  #     Z            | String  | null-terminated string
  #     B            | String  | bit string (MSB first)
  #     b            | String  | bit string (LSB first)
  #     H            | String  | hex string (high nibble first)
  #     h            | String  | hex string (low nibble first)
  #     u            | String  | UU-encoded string
  #     M            | String  | quoted-printable, MIME encoding (see RFC2045)
  #     m            | String  | base64 encoded string (RFC 2045) (default)
  #                  |         | base64 encoded string (RFC 4648) if followed by 0
  #     P            | String  | pointer to a structure (fixed-length string)
  #     p            | String  | pointer to a null-terminated string
  #
  #     Misc.        |         |
  #     Directive    | Returns | Meaning
  #     -----------------------------------------------------------------
  #     @            | ---     | skip to the offset given by the length argument
  #     X            | ---     | skip backward one byte
  #     x            | ---     | skip forward one byte
  #
  # The keyword *offset* can be given to start the decoding after skipping the
  # specified amount of bytes:
  #     "abc".unpack("C*") # => [97, 98, 99]
  #     "abc".unpack("C*", offset: 2) # => [99]
  #     "abc".unpack("C*", offset: 4) # => offset outside of string (ArgumentError)
  #
  # HISTORY
  #
  # *   J, J! j, and j! are available since Ruby 2.3.
  # *   Q_, Q!, q_, and q! are available since Ruby 2.1.
  # *   I!<, i!<, I!>, and i!> are available since Ruby 1.9.3.
  #
  def unpack: (String format, ?offset: Integer) -> Array[Integer | Float | String | nil]

  # <!--
  #   rdoc-file=pack.rb
  #   - str.unpack1(format)    ->  obj
  #   - str.unpack1(format, offset: anInteger)    ->  obj
  # -->
  # Decodes *str* (which may contain binary data) according to the format string,
  # returning the first value extracted.
  #
  # See also String#unpack, Array#pack.
  #
  # Contrast with String#unpack:
  #
  #     "abc \0\0abc \0\0".unpack('A6Z6')   #=> ["abc", "abc "]
  #     "abc \0\0abc \0\0".unpack1('A6Z6')  #=> "abc"
  #
  # In that case data would be lost but often it's the case that the array only
  # holds one value, especially when unpacking binary data. For instance:
  #
  #     "\xff\x00\x00\x00".unpack("l")         #=>  [255]
  #     "\xff\x00\x00\x00".unpack1("l")        #=>  255
  #
  # Thus unpack1 is convenient, makes clear the intention and signals the expected
  # return value to those reading the code.
  #
  # The keyword *offset* can be given to start the decoding after skipping the
  # specified amount of bytes:
  #     "abc".unpack1("C*") # => 97
  #     "abc".unpack1("C*", offset: 2) # => 99
  #     "abc".unpack1("C*", offset: 4) # => offset outside of string (ArgumentError)
  #
  def unpack1: (String format) -> (Integer | Float | String | nil)

  # <!--
  #   rdoc-file=string.c
  #   - upcase(*options) -> string
  # -->
  # Returns a string containing the upcased characters in `self`:
  #
  #     s = 'Hello World!' # => "Hello World!"
  #     s.upcase           # => "HELLO WORLD!"
  #
  # The casing may be affected by the given `options`; see [Case
  # Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#upcase!, String#downcase, String#downcase!.
  #
  def upcase: () -> String
            | (:ascii | :lithuanian | :turkic) -> String
            | (:lithuanian, :turkic) -> String
            | (:turkic, :lithuanian) -> String

  # <!--
  #   rdoc-file=string.c
  #   - upcase!(*options) -> self or nil
  # -->
  # Upcases the characters in `self`; returns `self` if any changes were made,
  # `nil` otherwise:
  #
  #     s = 'Hello World!' # => "Hello World!"
  #     s.upcase!          # => "HELLO WORLD!"
  #     s                  # => "HELLO WORLD!"
  #     s.upcase!          # => nil
  #
  # The casing may be affected by the given `options`; see [Case
  # Mapping](doc/case_mapping_rdoc.html).
  #
  # Related: String#upcase, String#downcase, String#downcase!.
  #
  def upcase!: () -> self?
             | (:ascii | :lithuanian | :turkic) -> self?
             | (:lithuanian, :turkic) -> self?
             | (:turkic, :lithuanian) -> self?

  # <!--
  #   rdoc-file=string.c
  #   - upto(other_string, exclusive = false) {|string| ... } -> self
  #   - upto(other_string, exclusive = false) -> new_enumerator
  # -->
  # With a block given, calls the block with each String value returned by
  # successive calls to String#succ; the first value is `self`, the next is
  # `self.succ`, and so on; the sequence terminates when value `other_string` is
  # reached; returns `self`:
  #
  #     'a8'.upto('b6') {|s| print s, ' ' } # => "a8"
  #
  # Output:
  #
  #     a8 a9 b0 b1 b2 b3 b4 b5 b6
  #
  # If argument `exclusive` is given as a truthy object, the last value is
  # omitted:
  #
  #     'a8'.upto('b6', true) {|s| print s, ' ' } # => "a8"
  #
  # Output:
  #
  #     a8 a9 b0 b1 b2 b3 b4 b5
  #
  # If `other_string` would not be reached, does not call the block:
  #
  #     '25'.upto('5') {|s| fail s }
  #     'aa'.upto('a') {|s| fail s }
  #
  # With no block given, returns a new Enumerator:
  #
  #     'a8'.upto('b6') # => #<Enumerator: "a8":upto("b6")>
  #
  def upto: (string other_str, ?boolish exclusive) -> Enumerator[String, self]
          | (string other_str, ?boolish exclusive) { (String s) -> void } -> self

  # <!--
  #   rdoc-file=string.c
  #   - str.valid_encoding?  -> true or false
  # -->
  # Returns true for a string which is encoded correctly.
  #
  #     "\xc2\xa1".force_encoding("UTF-8").valid_encoding?  #=> true
  #     "\xc2".force_encoding("UTF-8").valid_encoding?      #=> false
  #     "\x80".force_encoding("UTF-8").valid_encoding?      #=> false
  #
  def valid_encoding?: () -> bool

  private

  # <!--
  #   rdoc-file=string.c
  #   - String.new(string = '') -> new_string
  #   - String.new(string = '', encoding: encoding) -> new_string
  #   - String.new(string = '', capacity: size) -> new_string
  # -->
  # Returns a new String that is a copy of `string`.
  #
  # With no arguments, returns the empty string with the Encoding `ASCII-8BIT`:
  #     s = String.new
  #     s # => ""
  #     s.encoding # => #<Encoding:ASCII-8BIT>
  #
  # With the single String argument `string`, returns a copy of `string` with the
  # same encoding as `string`:
  #     s = String.new("Que veut dire \u{e7}a?")
  #     s # => "Que veut dire \u{e7}a?"
  #     s.encoding # => #<Encoding:UTF-8>
  #
  # Literal strings like `""` or here-documents always use [script
  # encoding](Encoding.html#class-Encoding-label-Script+encoding), unlike
  # String.new.
  #
  # With keyword `encoding`, returns a copy of `str` with the specified encoding:
  #     s = String.new(encoding: 'ASCII')
  #     s.encoding # => #<Encoding:US-ASCII>
  #     s = String.new('foo', encoding: 'ASCII')
  #     s.encoding # => #<Encoding:US-ASCII>
  #
  # Note that these are equivalent:
  #     s0 = String.new('foo', encoding: 'ASCII')
  #     s1 = 'foo'.force_encoding('ASCII')
  #     s0.encoding == s1.encoding # => true
  #
  # With keyword `capacity`, returns a copy of `str`; the given `capacity` may set
  # the size of the internal buffer, which may affect performance:
  #     String.new(capacity: 1) # => ""
  #     String.new(capacity: 4096) # => ""
  #
  # The `string`, `encoding`, and `capacity` arguments may all be used together:
  #
  #     String.new('hello', encoding: 'UTF-8', capacity: 25)
  #
  def initialize: (?string str, ?encoding: encoding, ?capacity: int) -> void

  # <!--
  #   rdoc-file=string.c
  #   - replace(other_string) -> self
  # -->
  # Replaces the contents of `self` with the contents of `other_string`:
  #
  #     s = 'foo'        # => "foo"
  #     s.replace('bar') # => "bar"
  #
  alias initialize_copy replace
end

interface _ArefFromStringToString
  def []: (String) -> String
end

type String::encode_fallback = Hash[String, String] | Proc | Method | _ArefFromStringToString