string.rb

# 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}[rdoc-ref:syntax/literals.rdoc@String+Literals].
# - A {heredoc literal}[rdoc-ref:syntax/literals.rdoc@Here+Document+Literals].
#
# You can convert certain objects to Strings with:
#
# - Method #String.
#
# Some +String+ methods modify +self+.
# Typically, a method whose name ends with <tt>!</tt> modifies +self+
# and returns +self+;
# often, a similarly named method (without the <tt>!</tt>)
# returns a new string.
#
# In general, if both bang and non-bang versions of a method exist,
# the bang method mutates and the non-bang method 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+ if any changes,
#   +nil+ otherwise.
# - String#gsub: Zero or more substitutions; returns a new string.
# - String#gsub!: Zero or more substitutions; returns +self+ if any changes,
#   +nil+ otherwise.
#
# Each of these methods takes:
#
# - A first argument, +pattern+ (String or Regexp),
#   that specifies the substring(s) to be replaced.
#
# - Either of the following:
#
#   - 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 the String#sub and String#gsub methods;
# the principles illustrated apply to all four substitution methods.
#
# <b>Argument +pattern+</b>
#
# 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"
#
# <b>+String+ +replacement+</b>
#
# If +replacement+ is a string, that string determines
# the replacing string that is 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:
#
# - <tt>\n</tt> (_n_ is a non-negative integer) refers to <tt>$n</tt>.
# - <tt>\k<name></tt> refers to the named capture +name+.
#
# See Regexp for details.
#
# Note that within the string +replacement+, a character combination
# such as <tt>$&</tt> is treated as ordinary text, not as
# a special match variable.
# However, you may refer to some special match variables using these
# combinations:
#
# - <tt>\&</tt> and <tt>\0</tt> correspond to <tt>$&</tt>,
#   which contains the complete matched text.
# - <tt>\'</tt> corresponds to <tt>$'</tt>,
#   which contains the string after the match.
# - <tt>\`</tt> corresponds to <tt>$`</tt>,
#   which contains the string before the match.
# - <tt>\\+</tt> corresponds to <tt>$+</tt>,
#   which contains the last capture group.
#
# See Regexp for details.
#
# Note that <tt>\\\\</tt> is interpreted as an escape, i.e., a single backslash.
#
# Note also that a string literal consumes backslashes.
# See {String Literals}[rdoc-ref:syntax/literals.rdoc@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 <tt>\&</tt> in
# +replacement+ with a double-quoted string literal, you need to write
# <tt>"..\\\\&.."</tt>.
#
# If you want to write a non-back-reference string <tt>\&</tt> in
# +replacement+, you need to first 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: <tt>"..\\\\\\\\&.."</tt>.
#
# You may want to use the block form to avoid excessive backslashes.
#
# <b>\Hash +replacement+</b>
#
# If the 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"
#
# <b>Block</b>
#
# 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 <tt>$1</tt>, <tt>$2</tt>, <tt>$`</tt>,
# <tt>$&</tt>, and <tt>$'</tt> are set appropriately.
#
# == Whitespace in Strings
#
# In the class +String+, _whitespace_ is defined as a contiguous sequence of characters
# consisting of any mixture of the following:
#
# - NL (null): <tt>"\x00"</tt>, <tt>"\u0000"</tt>.
# - HT (horizontal tab): <tt>"\x09"</tt>, <tt>"\t"</tt>.
# - LF (line feed): <tt>"\x0a"</tt>, <tt>"\n"</tt>.
# - VT (vertical tab): <tt>"\x0b"</tt>, <tt>"\v"</tt>.
# - FF (form feed): <tt>"\x0c"</tt>, <tt>"\f"</tt>.
# - CR (carriage return): <tt>"\x0d"</tt>, <tt>"\r"</tt>.
# - SP (space): <tt>"\x20"</tt>, <tt>" "</tt>.
#
#
# Whitespace is relevant for the following methods:
#
# - #lstrip, #lstrip!: Strip leading whitespace.
# - #rstrip, #rstrip!: Strip trailing whitespace.
# - #strip, #strip!: Strip leading and trailing whitespace.
#
# == +String+ Slices
#
# A _slice_ of a string is a substring selected by certain criteria.
#
# These instance methods utilize slicing:
#
# - String#[] (aliased as String#slice): Returns a slice copied from +self+.
# - String#[]=: Mutates +self+ with the slice replaced.
# - String#slice!: Mutates +self+ with the slice removed and returns the removed slice.
#
# Each of the above methods takes arguments that determine the slice
# to be copied or replaced.
#
# The arguments have several forms.
# For a string +string+, the forms are:
#
# - <tt>string[index]</tt>
# - <tt>string[start, length]</tt>
# - <tt>string[range]</tt>
# - <tt>string[regexp, capture = 0]</tt>
# - <tt>string[substring]</tt>
#
# <b><tt>string[index]</tt></b>
#
# When a non-negative integer argument +index+ is given,
# the slice is the 1-character substring found in +self+ at character offset +index+:
#
#   'bar'[0]      # => "b"
#   'bar'[2]      # => "r"
#   'bar'[20]     # => nil
#   'тест'[2]     # => "с"
#   'こんにちは'[4] # => "は"
#
# When a negative integer +index+ is given,
# the slice begins at the offset given by counting backward from the end of +self+:
#
#   'bar'[-3]      # => "b"
#   'bar'[-1]      # => "r"
#   'bar'[-20]     # => nil
#
# <b><tt>string[start, length]</tt></b>
#
# When non-negative integer arguments +start+ and +length+ are given,
# the slice begins at character offset +start+, if it exists,
# and continues for +length+ characters, if available:
#
#   'foo'[0, 2]      # => "fo"
#   'тест'[1, 2]     # => "ес"
#   'こんにちは'[2, 2] # => "にち"
#   # Zero length.
#   'foo'[2, 0]      # => ""
#   # Length not entirely available.
#   'foo'[1, 200]    # => "oo"
#   # Start out of range.
#   'foo'[4, 2]      # => nil
#
# Special case: if +start+ equals the length of +self+,
# the slice is a new empty string:
#
#   'foo'[3, 2]    # => ""
#   'foo'[3, 200]  # => ""
#
# When a negative +start+ and non-negative +length+ are given,
# the slice begins by counting backward from the end of +self+,
# and continues for +length+ characters, if available:
#
#   'foo'[-2, 2]     # => "oo"
#   'foo'[-2, 200]   # => "oo"
#   # Start out of range.
#   'foo'[-4, 2]     # => nil
#
# When a negative +length+ is given, there is no slice:
#
#   'foo'[1, -1]   # => nil
#   'foo'[-2, -1]  # => nil
#
# <b><tt>string[range]</tt></b>
#
# When a Range argument +range+ is given,
# it creates a substring of +string+ using the indices in +range+.
# The slice is then determined as above:
#
#   'foo'[0..1]     # => "fo"
#   'foo'[0, 2]     # => "fo"
#
#   'foo'[2...2]    # => ""
#   'foo'[2, 0]     # => ""
#
#   'foo'[1..200]   # => "oo"
#   'foo'[1, 200]   # => "oo"
#
#   'foo'[4..5]     # => nil
#   'foo'[4, 2]     # => nil
#
#   'foo'[-4..-3]   # => nil
#   'foo'[-4, 2]    # => nil
#
#   'foo'[3..4]     # => ""
#   'foo'[3, 2]     # => ""
#
#   'foo'[-2..-1]   # => "oo"
#   'foo'[-2, 2]    # => "oo"
#
#   'foo'[-2..197]  # => "oo"
#   'foo'[-2, 200]  # => "oo"
#
# <b><tt>string[regexp, capture = 0]</tt></b>
#
# When the Regexp argument +regexp+ is given,
# and the +capture+ argument is <tt>0</tt>,
# the slice is the first matching substring found in +self+:
#
#   'foo'[/o/]                # => "o"
#   'foo'[/x/]                # => nil
#   s = 'hello there'
#   s[/[aeiou](.)\1/]        # => "ell"
#   s[/[aeiou](.)\1/, 0]     # => "ell"
#
# If the argument +capture+ is provided and not <tt>0</tt>,
# it should be either a capture group index (integer)
# or a capture group name (String or Symbol);
# the slice is the specified capture (see Regexp@Groups and Captures):
#
#   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, there is no slice.
# If an invalid capture group name is given, +IndexError+ is raised.
#
# <b><tt>string[substring]</tt></b>
#
# When the single +String+ argument +substring+ is given,
# it returns the substring from +self+ if found, otherwise +nil+:
#
#   'foo'['oo'] # => "oo"
#   'foo'['xx'] # => nil
#
# == What's Here
#
# First, what's elsewhere. Class +String+:
#
# - Inherits from the {Object class}[rdoc-ref:Object@What-27s+Here].
# - Includes the {Comparable module}[rdoc-ref:Comparable@What-27s+Here].
#
# Here, class +String+ provides methods that are useful for:
#
# - {Creating a String}[rdoc-ref:String@Methods+for+Creating+a+String]
# - {Frozen/Unfrozen Strings}[rdoc-ref:String@Methods+for+a+Frozen-2FUnfrozen+String]
# - {Querying}[rdoc-ref:String@Methods+for+Querying]
# - {Comparing}[rdoc-ref:String@Methods+for+Comparing]
# - {Modifying a String}[rdoc-ref:String@Methods+for+Modifying+a+String]
# - {Converting to New String}[rdoc-ref:String@Methods+for+Converting+to+New+String]
# - {Converting to Non-String}[rdoc-ref:String@Methods+for+Converting+to+Non-String]
# - {Iterating}[rdoc-ref:String@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
#
# - #+@: Returns a string that is not frozen: +self+ if not frozen;
#   +self.dup+ otherwise.
# - #-@ (aliased as #dedup): 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 (aliased as #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_
#
# - #=~: 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
#
# - #== (aliased as #===): 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.
# - #<=>: 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 specified offset.
# - #<<: Returns +self+ concatenated with a given string or integer.
# - #append_as_bytes: Returns +self+ concatenated with strings without performing any
#   encoding validation or conversion.
#
# _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! (aliased as #next!): Returns +self+ modified to become its own successor.
# - #initialize_copy (aliased as #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 encoding to 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 the trailing record separator, if found; returns +self+ if any changes, +nil+ otherwise.
# - #chop!: Removes trailing newline characters 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 substrings.
# - #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 encoding to 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 <tt>\xNN</tt> notations replaced by <tt>\uNNNN</tt> notations
#   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 (aliased as #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 newline characters or the last character removed.
# - #squeeze: Returns a copy of +self+ with contiguous duplicate characters removed.
# - #[] (aliased as #slice): Returns a substring determined by a given index, start/length, range, regexp, or string.
# - #byteslice: Returns a substring determined by a given index, start/length, or range.
# - #chr: Returns the first character.
#
# _Duplication_
#
# - #to_s (aliased as #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+.
#
# <em>Characters, Bytes, and Clusters</em>
#
# - #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 the integer byte at the given index in +self+.
# - #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 is given, passes those substrings to the block.
#
# _Matching_
#
# - #scan: Returns an array of substrings matching a given regexp or string, or,
#   if a block is 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.
#
# <em>Strings and Symbols</em>
#
# - #inspect: Returns a copy of +self+, enclosed in double quotes, with special characters escaped.
# - #intern (aliased as #to_sym): 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; end