class String

Overview

A String represents an immutable sequence of UTF-8 characters.

A String is typically created with a string literal, enclosing UTF-8 characters in double quotes:

"hello world"

See String literals in the language reference.

A backslash can be used to denote some characters inside the string:

"\"" # double quote
"\\" # backslash
"\e" # escape
"\f" # form feed
"\n" # newline
"\r" # carriage return
"\t" # tab
"\v" # vertical tab

You can use a backslash followed by an u and four hexadecimal characters to denote a unicode codepoint written:

"\u0041" # == "A"

Or you can use curly braces and specify up to six hexadecimal numbers (0 to 10FFFF):

"\u{41}" # == "A"

A string can span multiple lines:

"hello
      world" # same as "hello\n      world"

Note that in the above example trailing and leading spaces, as well as newlines, end up in the resulting string. To avoid this, you can split a string into multiple lines by joining multiple literals with a backslash:

"hello " \
"world, " \
"no newlines" # same as "hello world, no newlines"

Alternatively, a backslash followed by a newline can be inserted inside the string literal:

"hello \
     world, \
     no newlines" # same as "hello world, no newlines"

In this case, leading whitespace is not included in the resulting string.

If you need to write a string that has many double quotes, parentheses, or similar characters, you can use alternative literals:

# Supports double quotes and nested parentheses
%(hello ("world")) # same as "hello (\"world\")"

# Supports double quotes and nested brackets
%[hello ["world"]] # same as "hello [\"world\"]"

# Supports double quotes and nested curlies
%{hello {"world"}} # same as "hello {\"world\"}"

# Supports double quotes and nested angles
%<hello <"world">> # same as "hello <\"world\">"

To create a String with embedded expressions, you can use string interpolation:

a = 1
b = 2
"sum = #{a + b}" # "sum = 3"

This ends up invoking Object#to_s(IO) on each expression enclosed by #{...}.

If you need to dynamically build a string, use String#build or IO::Memory.

Non UTF-8 valid strings

A string might end up being composed of bytes which form an invalid byte sequence according to UTF-8. This can happen if the string is created via one of the constructors that accept bytes, or when getting a string from String.build or IO::Memory. No exception will be raised, but every byte that doesn't start a valid UTF-8 byte sequence is interpreted as though it encodes the Unicode replacement character (U+FFFD) by itself. For example:

# here 255 is not a valid byte value in the UTF-8 encoding
string = String.new(Bytes[255, 97])
string.valid_encoding? # => false

# The first char here is the unicode replacement char
string.chars # => ['�', 'a']

One can also create strings with specific byte value in them by using octal and hexadecimal escape sequences:

# Octal escape sequences
"\101" # # => "A"
"\12"  # # => "\n"
"\1"   # string with one character with code point 1
"\377" # string with one byte with value 255

# Hexadecimal escape sequences
"\x41" # # => "A"
"\xFF" # string with one byte with value 255

The reason for allowing strings that don't have a valid UTF-8 sequence is that the world is full of content that isn't properly encoded, and having a program raise an exception or stop because of this is not good. It's better if programs are more resilient, but show a replacement character when there's an error in incoming data.

Note that this interpretation only applies to methods inside Crystal; calling #to_slice or #to_unsafe, e.g. when passing a string to a C library, will expose the invalid UTF-8 byte sequences. In particular, Regex's underlying engine may reject strings that are not valid UTF-8, or it may invoke undefined behavior on invalid strings. If this is undesired, #scrub could be used to remove the offending byte sequences first.

Included Modules

Defined in:

big/big_decimal.cr
big/big_float.cr
big/big_int.cr
json/to_json.cr
string.cr
string/grapheme.cr
string/grapheme/grapheme.cr
string/utf16.cr
uri/params/to_www_form.cr
yaml/to_yaml.cr

Constructors

Class Method Summary

Instance Method Summary

Instance methods inherited from module Comparable(String)

<(other : T) : Bool <, <=(other : T) <=, <=>(other : T) <=>, ==(other : T) ==, >(other : T) : Bool >, >=(other : T) >=, clamp(min, max)
clamp(range : Range) clamp

Instance methods inherited from class Reference

==(other : self)
==(other : JSON::Any)
==(other : YAML::Any)
==(other) ==, dup dup, hash(hasher) hash, initialize initialize, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference) : Bool
same?(other : Nil) same?, to_s(io : IO) : Nil to_s

Constructor methods inherited from class Reference

new new, unsafe_construct(address : Pointer, *args, **opts) : self unsafe_construct

Class methods inherited from class Reference

pre_initialize(address : Pointer) pre_initialize

Instance methods inherited from class Object

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other) ===, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

Class methods inherited from class Object

from_json(string_or_io, root : String)
from_json(string_or_io) from_json, from_yaml(string_or_io : String | IO) from_yaml

Macros inherited from class Object

class_getter(*names, &block) class_getter, class_getter!(*names) class_getter!, class_getter?(*names, &block) class_getter?, class_property(*names, &block) class_property, class_property!(*names) class_property!, class_property?(*names, &block) class_property?, class_setter(*names) class_setter, def_clone def_clone, def_equals(*fields) def_equals, def_equals_and_hash(*fields) def_equals_and_hash, def_hash(*fields) def_hash, delegate(*methods, to object) delegate, forward_missing_to(delegate) forward_missing_to, getter(*names, &block) getter, getter!(*names) getter!, getter?(*names, &block) getter?, property(*names, &block) property, property!(*names) property!, property?(*names, &block) property?, setter(*names) setter

Constructor Detail

def self.build(capacity = 64, &) : self #

Builds a String by creating a String::Builder with the given initial capacity, yielding it to the block and finally getting a String out of it. The String::Builder automatically resizes as needed.

str = String.build do |str|
  str << "hello "
  str << 1
end
str # => "hello 1"

[View source]
def self.from_json_object_key?(key : String) : String #

[View source]
def self.from_utf16(slice : Slice(UInt16)) : String #

Decodes the given slice UTF-16 sequence into a String.

Invalid values are encoded using the unicode replacement char with codepoint 0xfffd.

slice = Slice[104_u16, 105_u16, 32_u16, 55296_u16, 56485_u16]
String.from_utf16(slice) # => "hi 𐂥"

[View source]
def self.interpolation(value : String, char : Char) : String #

Implementation of string interpolation of a string and a char.

For example, this code will end up invoking this method:

char = '!'
"hello#{char}" # same as String.interpolation("hello", char)

In this case the implementation just does value + char.

NOTE there should never be a need to call this method instead of using string interpolation.


[View source]
def self.interpolation(char : Char, value : String) : String #

Implementation of string interpolation of a char and a string.

For example, this code will end up invoking this method:

char = '!'
"#{char}hello" # same as String.interpolation(char, "hello")

In this case the implementation just does char + value.

NOTE there should never be a need to call this method instead of using string interpolation.


[View source]
def self.interpolation(value : String) : String #

Implementation of string interpolation of a single string.

For example, this code will end up invoking this method:

value = "hello"
"#{value}" # same as String.interpolation(value)

In this case the implementation just returns the same string.

NOTE there should never be a need to call this method instead of using string interpolation.


[View source]
def self.interpolation(value) : String #

Implementation of string interpolation of a single non-string value.

For example, this code will end up invoking this method:

value = 123
"#{value}" # same as String.interpolation(value)

In this case the implementation just returns the result of calling value.to_s.

NOTE there should never be a need to call this method instead of using string interpolation.


[View source]
def self.interpolation(*values : String) : String #

Implementation of string interpolation of multiple string values.

For example, this code will end up invoking this method:

value1 = "hello"
value2 = "world"
"#{value1} #{value2}!" # same as String.interpolation(value1, " ", value2, "!")

In this case the implementation can pre-compute the needed string bytesize and so it's a bit more performant than interpolating non-string values.

NOTE there should never be a need to call this method instead of using string interpolation.


[View source]
def self.interpolation(*values : *T) : String forall T #

Implementation of string interpolation of multiple, possibly non-string values.

For example, this code will end up invoking this method:

value1 = "hello"
value2 = 123
"#{value1} #{value2}!" # same as String.interpolation(value1, " ", value2, "!")

In this case the implementation will call String.build with the given values.

NOTE there should never be a need to call this method instead of using string interpolation.


[View source]
def self.new(bytes : Bytes, encoding : String, invalid : Symbol | Nil = nil) : String #

Creates a new String from the given bytes, which are encoded in the given encoding.

The invalid argument can be:

  • nil: an exception is raised on invalid byte sequences
  • :skip: invalid byte sequences are ignored
slice = Slice.new(2, 0_u8)
slice[0] = 186_u8
slice[1] = 195_u8
String.new(slice, "GB2312") # => "好"

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def self.new(chars : Pointer(UInt8), bytesize, size = 0) #

Creates a new String from a pointer, indicating its bytesize count and, optionally, the UTF-8 codepoints count (size). Bytes will be copied from the pointer.

If the given size is zero, the amount of UTF-8 codepoints will be lazily computed when needed.

ptr = Pointer.malloc(4) { |i| ('a'.ord + i).to_u8 }
String.new(ptr, 2) # => "ab"

[View source]
def self.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node) #

[View source]
def self.new(chars : Pointer(UInt8)) #

Creates a String from a pointer. Bytes will be copied from the pointer.

This method is unsafe: the pointer must point to data that eventually contains a zero byte that indicates the ends of the string. Otherwise, the result of this method is undefined and might cause a segmentation fault.

This method is typically used in C bindings, where you get a char* from a library and the library guarantees that this pointer eventually has an ending zero byte.

ptr = Pointer.malloc(5) { |i| i == 4 ? 0_u8 : ('a'.ord + i).to_u8 }
String.new(ptr) # => "abcd"

[View source]
def self.new(slice : Bytes) #

Creates a String from the given slice. Bytes will be copied from the slice.

This method is always safe to call, and the resulting string will have the contents and size of the slice.

slice = Slice.new(4) { |i| ('a'.ord + i).to_u8 }
String.new(slice) # => "abcd"

[View source]
def self.new(capacity : Int, &) #

Creates a new String by allocating a buffer (Pointer(UInt8)) with the given capacity, then yielding that buffer. The block must return a tuple with the bytesize and size (UTF-8 codepoints count) of the String. If the returned size is zero, the UTF-8 codepoints count will be lazily computed.

The bytesize returned by the block must be less than or equal to the capacity given to this String, otherwise ArgumentError is raised.

If you need to build a String where the maximum capacity is unknown, use String#build.

str = String.new(4) do |buffer|
  buffer[0] = 'a'.ord.to_u8
  buffer[1] = 'b'.ord.to_u8
  {2, 2}
end
str # => "ab"

[View source]
def self.new(pull : JSON::PullParser) #

[View source]

Class Method Detail

def self.from_utf16(pointer : Pointer(UInt16)) : Tuple(String, Pointer(UInt16)) #

Decodes the given slice UTF-16 sequence into a String and returns the pointer after reading. The string ends when a zero value is found.

slice = Slice[104_u16, 105_u16, 0_u16, 55296_u16, 56485_u16, 0_u16]
String.from_utf16(slice) # => "hi\0000𐂥\u0000"
pointer = slice.to_unsafe
string, pointer = String.from_utf16(pointer)
string # => "hi"
string, pointer = String.from_utf16(pointer)
string # => "𐂥"

Invalid values are encoded using the unicode replacement char with codepoint 0xfffd.


[View source]

Instance Method Detail

def %(other) : String #

Interpolates other into the string using top-level ::sprintf.

"I have %d apples" % 5                                             # => "I have 5 apples"
"%s, %s, %s, D" % ['A', 'B', 'C']                                  # => "A, B, C, D"
"sum: %{one} + %{two} = %{three}" % {one: 1, two: 2, three: 1 + 2} # => "sum: 1 + 2 = 3"
"I have %<apples>s apples" % {apples: 4}                           # => "I have 4 apples"

[View source]
def *(times : Int) : String #

Makes a new String by adding str to itself times times.

"Developers! " * 4
# => "Developers! Developers! Developers! Developers! "

[View source]
def +(other : self) : String #

Concatenates str and other.

"abc" + "def" # => "abcdef"
"abc" + 'd'   # => "abcd"

[View source]
def +(char : Char) : String #

Concatenates str and other.

"abc" + "def" # => "abcdef"
"abc" + 'd'   # => "abcd"

[View source]
def <=>(other : self) : Int32 #

The comparison operator.

Compares this string with other, returning -1, 0 or 1 depending on whether this string is less, equal or greater than other.

Comparison is done byte-per-byte: if a byte is less than the other corresponding byte, -1 is returned and so on. This means two strings containing invalid UTF-8 byte sequences may compare unequal, even when they both produce the Unicode replacement character at the same string indices.

If the strings are of different lengths, and the strings are equal when compared up to the shortest length, then the longer string is considered greater than the shorter one.

"abcdef" <=> "abcde"   # => 1
"abcdef" <=> "abcdef"  # => 0
"abcdef" <=> "abcdefg" # => -1
"abcdef" <=> "ABCDEF"  # => 1

The comparison is case-sensitive. #compare is a case-insensitive alternative.


[View source]
def ==(other : self) : Bool #

Returns true if this string is equal to `other.

Equality is checked byte-per-byte: if any byte is different from the corresponding byte, it returns false. This means two strings containing invalid UTF-8 byte sequences may compare unequal, even when they both produce the Unicode replacement character at the same string indices.

Thus equality is case-sensitive, as it is with the comparison operator (#<=>). #compare offers a case-insensitive alternative.

"abcdef" == "abcde"   # => false
"abcdef" == "abcdef"  # => true
"abcdef" == "abcdefg" # => false
"abcdef" == "ABCDEF"  # => false

"abcdef".compare("ABCDEF", case_insensitive: true) == 0 # => true

[View source]
def =~(regex : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Int32 | Nil #

Tests whether str matches regex. If successful, it returns the position of the first match. If unsuccessful, it returns nil.

If the argument isn't a Regex, it returns nil.

"Haystack" =~ /ay/ # => 1
"Haystack" =~ /z/  # => nil

"Haystack" =~ 45 # => nil

[View source]
def =~(other, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Nil #

Tests whether str matches regex. If successful, it returns the position of the first match. If unsuccessful, it returns nil.

If the argument isn't a Regex, it returns nil.

"Haystack" =~ /ay/ # => 1
"Haystack" =~ /z/  # => nil

"Haystack" =~ 45 # => nil

[View source]
def [](start : Int, count : Int) : String #

Returns a substring starting from the start character of size count.

Negative start is added to self.size, thus it's treated as a character index counting from the end, -1 designating the last character.

Raises IndexError if start index is out of bounds. Raises ArgumentError if count is negative.


[View source]
def [](regex : Regex, group, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : String #

[View source]
def [](index : Int) : Char #

Returns the Char at the given index.

Negative indices can be used to start counting from the end of the string.

Raises IndexError if the index is out of bounds.

"hello"[0]  # => 'h'
"hello"[1]  # => 'e'
"hello"[-1] # => 'o'
"hello"[-2] # => 'l'
"hello"[5]  # raises IndexError

[View source]
def [](range : Range) : String #

Returns the substring indicated by range as span of character indices.

The substring ranges from self[range.begin] to self[range.end] (or self[range.end - 1] if the range is exclusive). It can be smaller than range.size if the end index is larger than self.size.

s = "abcde"
s[1..3] # => "bcd"
# range.end > s.size
s[3..7] # => "de"

Open ended ranges are clamped at the start and end of self, respectively.

# open ended ranges
s[2..] # => "cde"
s[..2] # => "abc"

Negative range values are added to self.size, thus they are treated as character indices counting from the end, -1 designating the last character.

# negative indices, both ranges are equivalent for `s`
s[1..3]   # => "bcd"
s[-4..-2] # => "bcd"
# Mixing negative and positive indices, both ranges are equivalent for `s`
s[1..-2] # => "bcd"
s[-4..3] # => "bcd"

Raises IndexError if the start index it out of range (range.begin > self.size || range.begin < -self.size). If range.begin == self.sizean empty string is returned. Ifrange.begin > range.end`, an empty string is returned.

# range.begin > array.size
s[6..10] # raise IndexError
# range.begin == s.size
s[5..10] # => ""
# range.begin > range.end
s[3..1]   # => ""
s[-2..-4] # => ""
s[-2..1]  # => ""
s[3..-4]  # => ""

[View source]
def [](str : String | Char) #

Returns str if str is found in this string.

"crystal"["cry"]  # => "cry"
"crystal"["ruby"] # raises NilAssertionError

[View source]
def [](regex : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : String #

[View source]
def []?(start : Int, count : Int) : String | Nil #

Like #[](Int, Int) but returns nil if the start index is out of bounds.


[View source]
def []?(regex : Regex, group, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : String | Nil #

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def []?(range : Range) : String | Nil #

Like #[](Range), but returns nil if range.begin is out of range.

"hello"[6..7]? # => nil
"hello"[6..]?  # => nil

[View source]
def []?(index : Int) : Char | Nil #

Returns the character at index or nil if it's out of range.

Negative indices can be used to start counting from the end of the string.

See #[] for a raising alternative.

"hello"[0]?  # => 'h'
"hello"[1]?  # => 'e'
"hello"[-1]? # => 'o'
"hello"[-2]? # => 'l'
"hello"[5]?  # => nil

[View source]
def []?(str : String | Char) #

Returns str if str is found in this string, or nil otherwise.

"crystal"["cry"]?  # => "cry"
"crystal"["ruby"]? # => nil

[View source]
def []?(regex : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : String | Nil #

[View source]
def ascii_only? : Bool #

Returns true if this String is comprised in its entirety by ASCII characters.

"hello".ascii_only? # => true
"你好".ascii_only?    # => false

[View source]
def blank? : Bool #

Returns true if this string consists exclusively of unicode whitespace.

"".blank?        # => true
"   ".blank?     # => true
"   a   ".blank? # => false

[View source]
def byte_at(index) : UInt8 #

Returns the byte at the given index.

Raises IndexError if the index is out of bounds.

"¥hello".byte_at(0)  # => 194
"¥hello".byte_at(1)  # => 165
"¥hello".byte_at(2)  # => 104
"¥hello".byte_at(-1) # => 111
"¥hello".byte_at(6)  # => 111
"¥hello".byte_at(7)  # raises IndexError

[View source]
def byte_at(index, &) #

Returns the byte at the given index, or yields if out of bounds.

"¥hello".byte_at(6) { "OUT OF BOUNDS" } # => 111
"¥hello".byte_at(7) { "OUT OF BOUNDS" } # => "OUT OF BOUNDS"

[View source]
def byte_at?(index) : UInt8 | Nil #

Returns the byte at the given index, or nil if out of bounds.

"¥hello".byte_at?(0)  # => 194
"¥hello".byte_at?(1)  # => 165
"¥hello".byte_at?(2)  # => 104
"¥hello".byte_at?(-1) # => 111
"¥hello".byte_at?(6)  # => 111
"¥hello".byte_at?(7)  # => nil

[View source]
def byte_index(byte : Int, offset : Int32 = 0) : Int32 | Nil #

Returns the index of the first occurrence of byte in the string, or nil if not present. If offset is present, it defines the position to start the search.

Negative offset can be used to start the search from the end of the string.

"Hello, World".byte_index(0x6f)             # => 4
"Hello, World".byte_index(0x5a)             # => nil
"Hello, World".byte_index(0x6f, 5)          # => 8
"💣".byte_index(0xA3)                        # => 3
"Dizzy Miss Lizzy".byte_index('z'.ord)      # => 2
"Dizzy Miss Lizzy".byte_index('z'.ord, 3)   # => 3
"Dizzy Miss Lizzy".byte_index('z'.ord, -4)  # => 13
"Dizzy Miss Lizzy".byte_index('z'.ord, -17) # => nil

[View source]
def byte_index(char : Char, offset = 0) : Int32 | Nil #

Returns the index of the first occurrence of char in the string, or nil if not present. If offset is present, it defines the position to start the search.

Negative offset can be used to start the search from the end of the string.

"Hello, World".byte_index('o')          # => 4
"Hello, World".byte_index('Z')          # => nil
"Hello, World".byte_index('o', 5)       # => 8
"Hi, 💣".byte_index('💣')                 # => 4
"Dizzy Miss Lizzy".byte_index('z')      # => 2
"Dizzy Miss Lizzy".byte_index('z', 3)   # => 3
"Dizzy Miss Lizzy".byte_index('z', -4)  # => 13
"Dizzy Miss Lizzy".byte_index('z', -17) # => nil

[View source]
def byte_index(search : String, offset = 0) : Int32 | Nil #

Returns the byte index of search in the string, or nil if the string is not present. If offset is present, it defines the position to start the search.

Negative offset can be used to start the search from the end of the string.

"¥hello".byte_index("hello")              # => 2
"hello".byte_index("world")               # => nil
"Dizzy Miss Lizzy".byte_index("izzy")     # => 1
"Dizzy Miss Lizzy".byte_index("izzy", 2)  # => 12
"Dizzy Miss Lizzy".byte_index("izzy", -4) # => 12
"Dizzy Miss Lizzy".byte_index("izzy", -3) # => nil

[View source]
def byte_index_to_char_index(index) : Int32 | Nil #

Returns the char index of a byte index, or nil if out of bounds.

It is valid to pass #bytesize to index, and in this case the answer will be the size of this string.


[View source]
def byte_slice(start : Int, count : Int) : String #

Returns a new string built from count bytes starting at start byte.

start can be negative to start counting from the end of the string. If count is bigger than the number of bytes from start to #bytesize, only remaining bytes are returned.

This method should be avoided, unless the string is proven to be ASCII-only (for example #ascii_only?), or the byte positions are known to be at character boundaries. Otherwise, multi-byte characters may be split, leading to an invalid UTF-8 encoding.

Raises IndexError if the start index is out of bounds.

Raises ArgumentError if count is negative.

"hello".byte_slice(0, 2)   # => "he"
"hello".byte_slice(0, 100) # => "hello"
"hello".byte_slice(-2, 3)  # => "he"
"hello".byte_slice(-2, 5)  # => "he"
"hello".byte_slice(-2, 5)  # => "he"
"¥hello".byte_slice(0, 2)  # => "¥"
"¥hello".byte_slice(2, 2)  # => "he"
"¥hello".byte_slice(0, 1)  # => "\xC2" (invalid UTF-8 character)
"¥hello".byte_slice(1, 1)  # => "\xA5" (invalid UTF-8 character)
"¥hello".byte_slice(1, 2)  # => "\xA5h" (invalid UTF-8 character)
"hello".byte_slice(6, 2)   # raises IndexError
"hello".byte_slice(-6, 2)  # raises IndexError
"hello".byte_slice(0, -2)  # raises ArgumentError

[View source]
def byte_slice(range : Range) : String #

Returns a new string built from byte in range.

Byte indices can be negative to start counting from the end of the string. If the end index is bigger than #bytesize, only remaining bytes are returned.

This method should be avoided, unless the string is proven to be ASCII-only (for example #ascii_only?), or the byte positions are known to be at character boundaries. Otherwise, multi-byte characters may be split, leading to an invalid UTF-8 encoding.

Raises IndexError if the range begin is out of bounds.

"hello".byte_slice(0..2)   # => "hel"
"hello".byte_slice(0..100) # => "hello"
"hello".byte_slice(-2..3)  # => "l"
"hello".byte_slice(-2..5)  # => "lo"
"¥hello".byte_slice(0...2) # => "¥"
"¥hello".byte_slice(2...4) # => "he"
"¥hello".byte_slice(0..0)  # => "\xC2" (invalid UTF-8 character)
"¥hello".byte_slice(1..1)  # => "\xA5" (invalid UTF-8 character)
"¥hello".byte_slice(1..2)  # => "\xA5h" (invalid UTF-8 character)
"hello".byte_slice(6..2)   # raises IndexError
"hello".byte_slice(-6..2)  # raises IndexError

[View source]
def byte_slice(start : Int) : String #

Returns a substring starting from the start byte.

start can be negative to start counting from the end of the string.

This method should be avoided, unless the string is proven to be ASCII-only (for example #ascii_only?), or the byte positions are known to be at character boundaries. Otherwise, multi-byte characters may be split, leading to an invalid UTF-8 encoding.

Raises IndexError if start index is out of bounds.

"hello".byte_slice(0)  # => "hello"
"hello".byte_slice(2)  # => "llo"
"hello".byte_slice(-2) # => "lo"
"¥hello".byte_slice(2) # => "hello"
"¥hello".byte_slice(1) # => "\xA5hello" (invalid UTF-8 character)
"hello".byte_slice(6)  # raises IndexError
"hello".byte_slice(-6) # raises IndexError

[View source]
def byte_slice?(start : Int, count : Int) : String | Nil #

Like #byte_slice(Int, Int) but returns Nil if the start index is out of bounds.

Raises ArgumentError if count is negative.

"hello".byte_slice?(0, 2)   # => "he"
"hello".byte_slice?(0, 100) # => "hello"
"hello".byte_slice?(6, 2)   # => nil
"hello".byte_slice?(-6, 2)  # => nil
"hello".byte_slice?(0, -2)  # raises ArgumentError

[View source]
def byte_slice?(range : Range) : String | Nil #

Like #byte_slice(Range) but returns Nil if range begin is out of bounds.

"hello".byte_slice?(0..2)   # => "hel"
"hello".byte_slice?(0..100) # => "hello"
"hello".byte_slice?(6..8)   # => nil
"hello".byte_slice?(-6..2)  # => nil

[View source]
def byte_slice?(start : Int) : String | Nil #

Returns a substring starting from the start byte.

start can be negative to start counting from the end of the string.

This method should be avoided, unless the string is proven to be ASCII-only (for example #ascii_only?), or the byte positions are known to be at character boundaries. Otherwise, multi-byte characters may be split, leading to an invalid UTF-8 encoding.

Returns nil if start index is out of bounds.

"hello".byte_slice?(0)  # => "hello"
"hello".byte_slice?(2)  # => "llo"
"hello".byte_slice?(-2) # => "lo"
"¥hello".byte_slice?(2) # => "hello"
"¥hello".byte_slice?(1) # => "\xA5hello" (invalid UTF-8 character)
"hello".byte_slice?(6)  # => nil
"hello".byte_slice?(-6) # => nil

[View source]
def bytes : Array(UInt8) #

Returns this string's bytes as an Array(UInt8).

"hello".bytes # => [104, 101, 108, 108, 111]
"你好".bytes    # => [228, 189, 160, 229, 165, 189]

[View source]
def bytesize : Int32 #

Returns the number of bytes in this string.

"hello".bytesize # => 5
"你好".bytesize    # => 6

[View source]
def camelcase(io : IO, options : Unicode::CaseOptions = Unicode::CaseOptions::None, *, lower : Bool = false) : Nil #

Writes an camelcased version of self to the given io.

If lower is true, lower camelcase will be written (the first letter is downcased).

io = IO::Memory.new
"eiffel_tower".camelcase io
io.to_s # => "EiffelTower"

[View source]
def camelcase(options : Unicode::CaseOptions = Unicode::CaseOptions::None, *, lower : Bool = false) : String #

Converts underscores to camelcase boundaries.

If lower is true, lower camelcase will be returned (the first letter is downcased).

"eiffel_tower".camelcase                                            # => "EiffelTower"
"empire_state_building".camelcase(lower: true)                      # => "empireStateBuilding"
"isolated_integer".camelcase(options: Unicode::CaseOptions::Turkic) # => "İsolatedİnteger"

[View source]
def capitalize(options : Unicode::CaseOptions = :none) : String #

Returns a new String with the first letter converted to uppercase and every subsequent letter converted to lowercase.

"hEllO".capitalize # => "Hello"

[View source]
def capitalize(io : IO, options : Unicode::CaseOptions = :none) : Nil #

Writes a capitalized version of self to the given io.

io = IO::Memory.new
"hEllO".capitalize io
io.to_s # => "Hello"

[View source]
def center(len : Int, char : Char = ' ') : String #

Adds instances of char to left and right of the string until it is at least size of len.

"Purple".center(8)      # => " Purple "
"Purple".center(8, '-') # => "-Purple-"
"Purple".center(9, '-') # => "-Purple--"
"Aubergine".center(8)   # => "Aubergine"

[View source]
def center(io : IO, len : Int, char : Char = ' ') : Nil #

Adds instances of char to left and right of the string until it is at least size of len, then appends the result to the given IO.

io = IO::Memory.new
"Purple".center(io, 9, '-')
io.to_s # => "-Purple--"

[View source]
def char_at(index : Int) : Char #

Returns the Char at the given index.

Negative indices can be used to start counting from the end of the string.

Raises IndexError if the index is out of bounds.

"hello".char_at(0)  # => 'h'
"hello".char_at(1)  # => 'e'
"hello".char_at(-1) # => 'o'
"hello".char_at(-2) # => 'l'
"hello".char_at(5)  # raises IndexError

[View source]
def char_at(index : Int, &) #

Returns the Char at the given index, or result of running the given block if out of bounds.

Negative indices can be used to start counting from the end of the string.

"hello".char_at(4) { 'x' }  # => 'o'
"hello".char_at(5) { 'x' }  # => 'x'
"hello".char_at(-1) { 'x' } # => 'o'
"hello".char_at(-5) { 'x' } # => 'h'
"hello".char_at(-6) { 'x' } # => 'x'

[View source]
def char_index_to_byte_index(index) #

Returns the byte index of a char index, or nil if out of bounds.

It is valid to pass #size to index, and in this case the answer will be the bytesize of this string.

"hello".char_index_to_byte_index(1) # => 1
"hello".char_index_to_byte_index(5) # => 5
"こんにちは".char_index_to_byte_index(1) # => 3
"こんにちは".char_index_to_byte_index(5) # => 15

[View source]
def chars : Array(Char) #

Returns an Array of all characters in the string.

"ab☃".chars # => ['a', 'b', '☃']

[View source]
def check_no_null_byte(name = nil) : self #

Raises an ArgumentError if self has null bytes. Returns self otherwise.

This method should sometimes be called before passing a String to a C function.


[View source]
def chomp(suffix : Char) : String #

Returns a new String with suffix removed from the end of the string. If suffix is '\n' then "\r\n" is also removed if the string ends with it.

"hello".chomp('o') # => "hell"
"hello".chomp('a') # => "hello"

[View source]
def chomp(suffix : String) : String #

Returns a new String with suffix removed from the end of the string. If suffix is "\n" then "\r\n" is also removed if the string ends with it.

"hello".chomp("llo") # => "he"
"hello".chomp("ol")  # => "hello"

[View source]
def chomp : String #

Returns a new String with the last carriage return removed (that is, it will remove \n, \r, and \r\n).

"string\r\n".chomp # => "string"
"string\n\r".chomp # => "string\n"
"string\n".chomp   # => "string"
"string".chomp     # => "string"
"x".chomp.chomp    # => "x"

[View source]
def clone : String #

Returns self.


[View source]
def codepoint_at(index) : Int32 #

Returns the codepoint of the character at the given index.

Negative indices can be used to start counting from the end of the string.

Raises IndexError if the index is out of bounds.

See also: Char#ord.

"hello".codepoint_at(0)  # => 104
"hello".codepoint_at(-1) # => 111
"hello".codepoint_at(5)  # raises IndexError

[View source]
def codepoints : Array(Int32) #

Returns an Array of the codepoints that make the string.

"ab☃".codepoints # => [97, 98, 9731]

See also: Char#ord.


[View source]
def compare(other : String, case_insensitive = false, options : Unicode::CaseOptions = :none) : Int32 #

Compares this string with other, returning -1, 0 or 1 depending on whether this string is less, equal or greater than other, optionally in a case_insensitive manner.

Case-sensitive comparisons (case_insensitive == false) are equivalent to #<=> and are always done byte-per-byte.

"abcdef".compare("abcde")   # => 1
"abcdef".compare("abcdef")  # => 0
"abcdef".compare("abcdefg") # => -1
"abcdef".compare("ABCDEF")  # => 1

"abcdef".compare("ABCDEF", case_insensitive: true) # => 0
"abcdef".compare("ABCDEG", case_insensitive: true) # => -1

"heIIo".compare("heııo", case_insensitive: true, options: Unicode::CaseOptions::Turkic) # => 0
"Baffle".compare("baffle", case_insensitive: true, options: Unicode::CaseOptions::Fold)   # => 0

Case-sensitive only comparison is provided by the comparison operator #<=>.


[View source]
def count(&) : Int32 #

Yields each char in this string to the block, returns the number of times the block returned a truthy value.

"aabbcc".count &.in?('a', 'b') # => 4

[View source]
def count(other : Char) : Int32 #

Counts the occurrences of other char in this string.

"aabbcc".count('a') # => 2

[View source]
def count(*sets) : Int32 #

Sets should be a list of strings following the rules described at Char#in_set?. Returns the number of characters in this string that match the given set.


[View source]
def delete(&) : String #

Yields each char in this string to the block. Returns a new String with all characters for which the block returned a truthy value removed.

"aabbcc".delete &.in?('a', 'b') # => "cc"

[View source]
def delete(char : Char) : String #

Returns a new String with all occurrences of char removed.

"aabbcc".delete('b') # => "aacc"

[View source]
def delete(*sets) : String #

Sets should be a list of strings following the rules described at Char#in_set?. Returns a new String with all characters that match the given set removed.

"aabbccdd".delete("a-c") # => "dd"

[View source]
def delete_at(start : Int, count : Int) : String #

Returns a new string that results from deleting count characters starting at start.

"abcdefg".delete_at(1, 3) # => "aefg"

Deleting more characters than those in the string is valid, and just results in deleting up to the last character:

"abcdefg".delete_at(3, 10) # => "abc"

A negative start counts from the end of the string:

"abcdefg".delete_at(-3, 2) # => "abcdg"

If count is negative, ArgumentError is raised.

If start is outside the bounds of the string, ArgumentError is raised.

However, start can be the position that is exactly the end of the string:

"abcd".delete_at(4, 3) # => "abcd"

[View source]
def delete_at(range : Range) : String #

Returns a new string that results from deleting characters at the given range.

"abcdef".delete_at(1..3) # => "aef"

Negative indices can be used to start counting from the end of the string:

"abcdef".delete_at(-3..-2) # => "abcf"

Raises IndexError if any index is outside the bounds of this string.


[View source]
def delete_at(index : Int) : String #

Returns a new string that results from deleting the character at the given index.

"abcde".delete_at(0) # => "bcde"
"abcde".delete_at(2) # => "abde"
"abcde".delete_at(4) # => "abcd"

A negative index counts from the end of the string:

"abcde".delete_at(-2) # => "abce"

If index is outside the bounds of the string, IndexError is raised.


[View source]
def delete_at(*, index start : Int, count : Int) : String #

Returns a new string that results from deleting count characters starting at start.

"abcdefg".delete_at(1, 3) # => "aefg"

Deleting more characters than those in the string is valid, and just results in deleting up to the last character:

"abcdefg".delete_at(3, 10) # => "abc"

A negative start counts from the end of the string:

"abcdefg".delete_at(-3, 2) # => "abcdg"

If count is negative, ArgumentError is raised.

If start is outside the bounds of the string, ArgumentError is raised.

However, start can be the position that is exactly the end of the string:

"abcd".delete_at(4, 3) # => "abcd"

DEPRECATED Use #delete_at(start, count) instead


[View source]
def downcase(options : Unicode::CaseOptions = :none) : String #

Returns a new String with each uppercase letter replaced with its lowercase counterpart.

"hEllO".downcase # => "hello"

[View source]
def downcase(io : IO, options : Unicode::CaseOptions = :none) : Nil #

Writes a downcased version of self to the given io.

io = IO::Memory.new
"hEllO".downcase io
io.to_s # => "hello"

[View source]
def dump(io : IO) : Nil #

Returns a representation of self as an ASCII-compatible Crystal string literal, wrapped in double quotes.

Non-printable characters (see Char#printable?) and non-ASCII characters (codepoints larger U+007F) are escaped.

"\u{1f48e} - à la carte\n".dump # => %("\\u{1F48E} - \\u00E0 la carte\\n")

See Char#unicode_escape for the format used to escape characters without a special escape sequence.


[View source]
def dump : String #

Returns a representation of self as an ASCII-compatible Crystal string literal, wrapped in double quotes.

Non-printable characters (see Char#printable?) and non-ASCII characters (codepoints larger U+007F) are escaped.

"\u{1f48e} - à la carte\n".dump # => %("\\u{1F48E} - \\u00E0 la carte\\n")

See Char#unicode_escape for the format used to escape characters without a special escape sequence.


[View source]
def dump_unquoted : String #

Returns a representation of self as the content of an ASCII-compatible Crystal string literal without delimiters.

Non-printable characters (see Char#printable?) and non-ASCII characters (codepoints larger U+007F) are escaped.

"\u{1f48e} - à la carte\n".dump_unquoted # => %(\\u{1F48E} - \\u00E0 la carte\\n)

See Char#unicode_escape for the format used to escape characters without a special escape sequence.


[View source]
def dup : String #

Returns self.


[View source]
def each_byte(&) #

Yields each byte in the string to the block.

array = [] of UInt8
"ab☃".each_byte do |byte|
  array << byte
end
array # => [97, 98, 226, 152, 131]

[View source]
def each_byte #

Returns an Iterator over each byte in the string.

bytes = "ab☃".each_byte
bytes.next # => 97
bytes.next # => 98
bytes.next # => 226
bytes.next # => 152
bytes.next # => 131

[View source]
def each_char(&) : Nil #

Yields each character in the string to the block.

array = [] of Char
"ab☃".each_char do |char|
  array << char
end
array # => ['a', 'b', '☃']

[View source]
def each_char #

Returns an Iterator over each character in the string.

chars = "ab☃".each_char
chars.next # => 'a'
chars.next # => 'b'
chars.next # => '☃'

[View source]
def each_char_with_index(offset = 0, &) #

Yields each character and its index in the string to the block.

array = [] of Tuple(Char, Int32)
"ab☃".each_char_with_index do |char, index|
  array << {char, index}
end
array # => [{'a', 0}, {'b', 1}, {'☃', 2}]

Accepts an optional offset parameter, which tells it to start counting from there.


[View source]
def each_codepoint(&) #

Yields each codepoint to the block.

array = [] of Int32
"ab☃".each_codepoint do |codepoint|
  array << codepoint
end
array # => [97, 98, 9731]

See also: Char#ord.


[View source]
def each_codepoint #

Returns an Iterator for each codepoint.

codepoints = "ab☃".each_codepoint
codepoints.next # => 97
codepoints.next # => 98
codepoints.next # => 9731

See also: Char#ord.


[View source]
def each_grapheme(& : Grapheme -> _) : Nil #

Yields each Unicode extended grapheme cluster in this string.

Grapheme clusters correspond to "user-perceived characters" and are defined in Unicode Standard Annex #29. A cluster can consist of multiple code points which together form a single glyph.

"a👍🏼à".each_grapheme do |cluster|
  p! cluster
end
  • #graphemes collects all grapheme clusters in an array

EXPERIMENTAL The grapheme API is still under development. Join the discussion at #11610.


[View source]
def each_grapheme : Iterator(Grapheme) #

Returns an iterator of this string split into Unicode extended grapheme clusters.

Grapheme clusters correspond to "user-perceived characters" and are defined in Unicode Standard Annex #29. A cluster can consist of multiple code points which together form a single glyph.

"a👍🏼à".each_grapheme.to_a # => [String::Grapheme('a'), String::Grapheme("👍🏼"), String::Grapheme("à")]
  • #graphemes collects all grapheme clusters in an array

EXPERIMENTAL The grapheme API is still under development. Join the discussion at #11610.


[View source]
def each_line(chomp = true, &block : String -> ) : Nil #

Splits the string after each newline and yields each line to a block.

haiku = "the first cold shower
even the monkey seems to want
a little coat of straw"
haiku.each_line do |stanza|
  puts stanza
end
# output:
# the first cold shower
# even the monkey seems to want
# a little coat of straw

[View source]
def each_line(chomp = true) #

Returns an Iterator which yields each line of this string (see String#each_line).


[View source]
def empty? : Bool #

Returns true if this is the empty string, "".


[View source]
def encode(encoding : String, invalid : Symbol | Nil = nil) : Bytes #

Returns a slice of bytes containing this string encoded in the given encoding.

The invalid argument can be:

  • nil: an exception is raised on invalid byte sequences
  • :skip: invalid byte sequences are ignored
"好".encode("GB2312") # => Bytes[186, 195]
"好".bytes            # => [229, 165, 189]

[View source]
def ends_with?(str : String) : Bool #

Returns true if this string ends with the given str.

"hello".ends_with?("o")  # => true
"hello".ends_with?("lo") # => true
"hello".ends_with?("ll") # => false

[View source]
def ends_with?(char : Char) : Bool #

Returns true if this string ends with the given char.

"hello".ends_with?('o') # => true
"hello".ends_with?('l') # => false

[View source]
def ends_with?(re : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Bool #

Returns true if the regular expression re matches at the end of this string.

"22hello".ends_with?(/[0-9]/) # => false
"22hello".ends_with?(/[a-z]/) # => true
"22h".ends_with?(/[a-z]/)     # => true
"22h".ends_with?(/[A-Z]/)     # => false
"22h".ends_with?(/[a-z]{2}/)  # => false
"22hh".ends_with?(/[a-z]{2}/) # => true

[View source]
def grapheme_size : Int32 #

Returns the number of Unicode extended graphemes clusters in this string.

EXPERIMENTAL The grapheme API is still under development. Join the discussion at #11610.


[View source]
def graphemes : Array(Grapheme) #

Returns this string split into Unicode extended grapheme clusters.

Grapheme clusters correspond to "user-perceived characters" and are defined in Unicode Standard Annex #29. A cluster can consist of multiple code points which together form a single glyph.

"a👍🏼à".graphemes # => [String::Grapheme('a'), String::Grapheme("👍🏼"), String::Grapheme("à")]
  • #each_grapheme iterates the grapheme clusters without allocating an array

EXPERIMENTAL The grapheme API is still under development. Join the discussion at #11610.


[View source]
def gsub(string : String, &) : String #

Returns a String where all occurrences of the given string are replaced with the block's value.

"hello yellow".gsub("ll") { "dd" } # => "heddo yeddow"

[View source]
def gsub(pattern : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None, &) : String #

Returns a String where all occurrences of the given pattern are replaced by the block value's value.

"hello".gsub(/./) { |s| s[0].ord.to_s + ' ' } # => "104 101 108 108 111 "

[View source]
def gsub(&block : Char -> _) : String #

Returns a String where each character yielded to the given block is replaced by the block's return value.

"hello".gsub { |char| char + 1 } # => "ifmmp"
"hello".gsub { "hi" }            # => "hihihihihi"

[View source]
def gsub(char : Char, replacement) : String #

Returns a String where all occurrences of the given char are replaced with the given replacement.

"hello".gsub('l', "lo")      # => "heloloo"
"hello world".gsub('o', 'a') # => "hella warld"

[View source]
def gsub(pattern : Regex, hash : Hash(String, _) | NamedTuple, options : Regex::MatchOptions = Regex::MatchOptions::None) : String #

Returns a String where all occurrences of the given pattern are replaced with a hash of replacements. If the hash contains the matched pattern, the corresponding value is used as a replacement. Otherwise the match is not included in the returned string.

# "he" and "l" are matched and replaced,
# but "o" is not and so is not included
"hello".gsub(/(he|l|o)/, {"he": "ha", "l": "la"}) # => "halala"

[View source]
def gsub(string : String, replacement) : String #

Returns a String where all occurrences of the given string are replaced with the given replacement.

"hello yellow".gsub("ll", "dd") # => "heddo yeddow"

[View source]
def gsub(pattern : Regex, replacement, backreferences = true, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : String #

Returns a String where all occurrences of the given pattern are replaced with the given replacement.

"hello".gsub(/[aeiou]/, '*') # => "h*ll*"

Within replacement, the special match variable $~ will not refer to the current match.

If backreferences is true (the default value), replacement can include backreferences:

"hello".gsub(/[aeiou]/, "(\\0)") # => "h(e)ll(o)"

When substitution is performed, any backreferences found in replacement will be replaced with the contents of the corresponding capture group in pattern. Backreferences to capture groups that were not present in pattern or that did not match will be skipped. See Regex for information about capture groups.

Backreferences are expressed in the form "\\d", where d is a group number, or "\\k<name>" where name is the name of a named capture group. A sequence of literal characters resembling a backreference can be expressed by placing "\\" before the sequence.

"foo".gsub(/o/, "x\\0x")                  # => "fxoxxox"
"foofoo".gsub(/(?<bar>oo)/, "|\\k<bar>|") # => "f|oo|f|oo|"
"foo".gsub(/o/, "\\\\0")                  # => "f\\0\\0"

Raises ArgumentError if an incomplete named back-reference is present in replacement.

Raises IndexError if a named group referenced in replacement is not present in pattern.


[View source]
def gsub(hash : Hash(Char, _)) : String #

Returns a String where all chars in the given hash are replaced by the corresponding hash values.

"hello".gsub({'e' => 'a', 'l' => 'd'}) # => "haddo"

[View source]
def gsub(tuple : NamedTuple) : String #

Returns a String where all chars in the given named tuple are replaced by the corresponding tuple values.

"hello".gsub({e: 'a', l: 'd'}) # => "haddo"

[View source]
def has_back_references? #

This returns true if this string has '\\' in it. It might not be a back reference, but '\\' is probably used for back references, so this check is faster than parsing the whole thing.


[View source]
def hash(hasher) #

See Object#hash(hasher)


[View source]
def hexbytes : Bytes #

Interprets this string as containing a sequence of hexadecimal values and decodes it as a slice of bytes. Two consecutive bytes in the string represent a byte in the returned slice.

Raises ArgumentError if this string does not denote an hexstring.

"0102031aff".hexbytes  # => Bytes[1, 2, 3, 26, 255]
"1".hexbytes           # raises ArgumentError
"hello world".hexbytes # raises ArgumentError

[View source]
def hexbytes? : Bytes | Nil #

Interprets this string as containing a sequence of hexadecimal values and decodes it as a slice of bytes. Two consecutive bytes in the string represent a byte in the returned slice.

Returns nil if this string does not denote an hexstring.

"0102031aff".hexbytes?  # => Bytes[1, 2, 3, 26, 255]
"1".hexbytes?           # => nil
"hello world".hexbytes? # => nil

[View source]
def includes?(search : Char | String) : Bool #

Returns true if the string contains search.

"Team".includes?('i')            # => false
"Dysfunctional".includes?("fun") # => true

[View source]
def index(search : Char, offset = 0) : Int32 | Nil #

Returns the index of the first occurrence of search in the string, or nil if not present. If offset is present, it defines the position to start the search.

"Hello, World".index('o')    # => 4
"Hello, World".index('Z')    # => nil
"Hello, World".index("o", 5) # => 8
"Hello, World".index("H", 2) # => nil
"Hello, World".index(/[ ]+/) # => 6
"Hello, World".index(/\d+/)  # => nil

[View source]
def index(search : String, offset = 0) #

Returns the index of the first occurrence of search in the string, or nil if not present. If offset is present, it defines the position to start the search.

"Hello, World".index('o')    # => 4
"Hello, World".index('Z')    # => nil
"Hello, World".index("o", 5) # => 8
"Hello, World".index("H", 2) # => nil
"Hello, World".index(/[ ]+/) # => 6
"Hello, World".index(/\d+/)  # => nil

[View source]
def index(search : Regex, offset = 0, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Int32 | Nil #

Returns the index of the first occurrence of search in the string, or nil if not present. If offset is present, it defines the position to start the search.

"Hello, World".index('o')    # => 4
"Hello, World".index('Z')    # => nil
"Hello, World".index("o", 5) # => 8
"Hello, World".index("H", 2) # => nil
"Hello, World".index(/[ ]+/) # => 6
"Hello, World".index(/\d+/)  # => nil

[View source]
def index!(search, offset = 0) : Int32 #

Returns the index of the first occurrence of search in the string. If offset is present, it defines the position to start the search.

Raises Enumerable::NotFoundError if search does not occur in self.

"Hello, World".index!('o')    # => 4
"Hello, World".index!('Z')    # raises Enumerable::NotFoundError
"Hello, World".index!("o", 5) # => 8
"Hello, World".index!("H", 2) # raises Enumerable::NotFoundError
"Hello, World".index!(/[ ]+/) # => 6
"Hello, World".index!(/\d+/)  # raises Enumerable::NotFoundError

[View source]
def index!(search : Regex, offset = 0, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Int32 #

Returns the index of the first occurrence of search in the string. If offset is present, it defines the position to start the search.

Raises Enumerable::NotFoundError if search does not occur in self.

"Hello, World".index!('o')    # => 4
"Hello, World".index!('Z')    # raises Enumerable::NotFoundError
"Hello, World".index!("o", 5) # => 8
"Hello, World".index!("H", 2) # raises Enumerable::NotFoundError
"Hello, World".index!(/[ ]+/) # => 6
"Hello, World".index!(/\d+/)  # raises Enumerable::NotFoundError

[View source]
def insert(index : Int, other : Char) : String #

Returns a new String that results of inserting other in self at index. Negative indices count from the end of the string, and insert after the given index.

Raises IndexError if the index is out of bounds.

"abcd".insert(0, 'X')  # => "Xabcd"
"abcd".insert(3, 'X')  # => "abcXd"
"abcd".insert(4, 'X')  # => "abcdX"
"abcd".insert(-3, 'X') # => "abXcd"
"abcd".insert(-1, 'X') # => "abcdX"

"abcd".insert(5, 'X')  # raises IndexError
"abcd".insert(-6, 'X') # raises IndexError

[View source]
def insert(index : Int, other : String) : String #

Returns a new String that results of inserting other in self at index. Negative indices count from the end of the string, and insert after the given index.

Raises IndexError if the index is out of bounds.

"abcd".insert(0, "FOO")  # => "FOOabcd"
"abcd".insert(3, "FOO")  # => "abcFOOd"
"abcd".insert(4, "FOO")  # => "abcdFOO"
"abcd".insert(-3, "FOO") # => "abFOOcd"
"abcd".insert(-1, "FOO") # => "abcdFOO"

"abcd".insert(5, "FOO")  # raises IndexError
"abcd".insert(-6, "FOO") # raises IndexError

[View source]
def inspect(io : IO) : Nil #

Returns a representation of self as a Crystal string literal, wrapped in double quotes.

Non-printable characters (see Char#printable?) are escaped.

"\u{1f48e} - à la carte\n".inspect # => %("\u{1F48E} - à la carte\\n")

See Char#unicode_escape for the format used to escape characters without a special escape sequence.


[View source]
def inspect : String #

Returns a representation of self as a Crystal string literal, wrapped in double quotes.

Non-printable characters (see Char#printable?) are escaped.

"\u{1f48e} - à la carte\n".inspect # => %("\u{1F48E} - à la carte\\n")

See Char#unicode_escape for the format used to escape characters without a special escape sequence.


[View source]
def inspect_unquoted(io : IO) : Nil #

Returns a representation of self as the content of a Crystal string literal without delimiters.

Non-printable characters (see Char#printable?) are escaped.

"\u{1f48e} - à la carte\n".inspect_unquoted # => %(\u{1F48E} - à la carte\\n)

See Char#unicode_escape for the format used to escape characters without a special escape sequence.


[View source]
def inspect_unquoted : String #

Returns a representation of self as the content of a Crystal string literal without delimiters.

Non-printable characters (see Char#printable?) are escaped.

"\u{1f48e} - à la carte\n".inspect_unquoted # => %(\u{1F48E} - à la carte\\n)

See Char#unicode_escape for the format used to escape characters without a special escape sequence.


[View source]
def lchop(prefix : Char | String) : String #

Returns a new String with prefix removed from the beginning of the string.

"hello".lchop('h')   # => "ello"
"hello".lchop('g')   # => "hello"
"hello".lchop("hel") # => "lo"
"hello".lchop("eh")  # => "hello"

[View source]
def lchop : String #

Returns a new String with the first char removed from it. Applying lchop to an empty string returns an empty string.

"hello".lchop # => "ello"
"".lchop      # => ""

[View source]
def lchop?(prefix : Char | String) : String | Nil #

Returns a new String with prefix removed from the beginning of the string if possible, else returns nil.

"hello".lchop?('h')   # => "ello"
"hello".lchop?('g')   # => nil
"hello".lchop?("hel") # => "lo"
"hello".lchop?("eh")  # => nil

[View source]
def lchop? : String | Nil #

Returns a new String with the first char removed from it if possible, else returns nil.

"hello".lchop? # => "ello"
"".lchop?      # => nil

[View source]
def lines(chomp = true) : Array(String) #

[View source]
def ljust(len : Int, char : Char = ' ') : String #

Adds instances of char to right of the string until it is at least size of len.

"Purple".ljust(8)      # => "Purple  "
"Purple".ljust(8, '-') # => "Purple--"
"Aubergine".ljust(8)   # => "Aubergine"

[View source]
def ljust(io : IO, len : Int, char : Char = ' ') : Nil #

Adds instances of char to right of the string until it is at least size of len, and then appends the result to the given IO.

io = IO::Memory.new
"Purple".ljust(io, 8, '-')
io.to_s # => "Purple--"

[View source]
def lstrip(char : Char) : String #

Returns a new string with leading occurrences of char removed.

"aaabcdaaa".lstrip('a') # => "bcdaaa"

[View source]
def lstrip(chars : String) : String #

Returns a new string where leading occurrences of any char in chars are removed. The chars argument is not a suffix; rather; all combinations of its values are stripped.

"bcadefcba".lstrip("abc") # => "defcba"

[View source]
def lstrip : String #

Returns a new String with leading whitespace removed.

"    hello    ".lstrip # => "hello    "
"\tgoodbye\r\n".lstrip # => "goodbye\r\n"

[View source]
def lstrip(&block : Char -> _) : String #

Returns a new string where leading characters for which the block returns a truthy value are removed.

"bcadefcba".lstrip { |c| 'a' <= c <= 'c' } # => "defcba"

[View source]
def match(regex : Regex, pos = 0, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Regex::MatchData | Nil #

Finds matches of regex starting at pos and updates $~ to the result.

"foo".match(/foo/) # => Regex::MatchData("foo")
$~                 # => Regex::MatchData("foo")

"foo".match(/bar/) # => nil
$~                 # raises Exception

[View source]
def match!(regex : Regex, pos = 0, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Regex::MatchData #

Finds matches of regex starting at pos and updates $~ to the result. Raises Regex::Error if there are no matches.

"foo".match!(/foo/) # => Regex::MatchData("foo")
$~                  # => Regex::MatchData("foo")

"foo".match!(/bar/) # => raises Exception

[View source]
def match_full(regex : Regex) : Regex::MatchData | Nil #

Matches the regular expression regex against the entire string and returns the resulting MatchData. It also updates $~ with the result.

"foo".match_full(/foo/)  # => Regex::MatchData("foo")
$~                       # => Regex::MatchData("foo")
"fooo".match_full(/foo/) # => nil
$~                       # raises Exception

[View source]
def match_full!(regex : Regex) : Regex::MatchData | Nil #

Matches the regular expression regex against the entire string and returns the resulting MatchData. It also updates $~ with the result. Raises Regex::Error if there are no matches.

"foo".match_full!(/foo/)  # => Regex::MatchData("foo")
$~                        # => Regex::MatchData("foo")
"fooo".match_full!(/foo/) # Regex::Error
$~                        # raises Exception

[View source]
def matches?(regex : Regex, pos = 0, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Bool #

Finds match of regex like #match, but it returns Bool value. It neither returns MatchData nor assigns it to the $~ variable.

"foo".matches?(/bar/) # => false
"foo".matches?(/foo/) # => true

# `$~` is not set even if last match succeeds.
$~ # raises Exception

[View source]
def matches_full?(regex : Regex) : Bool #

Returns true if the regular expression regex matches this string entirely.

"foo".matches_full?(/foo/)  # => true
"fooo".matches_full?(/foo/) # => false

# `$~` is not set even if last match succeeds.
$~ # raises Exception

[View source]
def partition(search : Char | String) : Tuple(String, String, String) #

Searches separator or pattern (Regex) in the string, and returns a Tuple with the part before it, the match, and the part after it. If it is not found, returns str followed by two empty strings.

"hello".partition("l") # => {"he", "l", "lo"}
"hello".partition("x") # => {"hello", "", ""}

[View source]
def partition(search : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Tuple(String, String, String) #

Searches separator or pattern (Regex) in the string, and returns a Tuple with the part before it, the match, and the part after it. If it is not found, returns str followed by two empty strings.

"hello".partition("l") # => {"he", "l", "lo"}
"hello".partition("x") # => {"hello", "", ""}

[View source]
def presence : self | Nil #

Returns self unless #blank? is true in which case it returns nil.

"a".presence         # => "a"
"".presence          # => nil
"   ".presence       # => nil
"    a    ".presence # => "    a    "
nil.presence         # => nil

config = {"empty" => ""}
config["empty"]?.presence || "default"   # => "default"
config["missing"]?.presence || "default" # => "default"

See also: Nil#presence.


[View source]
def pretty_print(pp : PrettyPrint) : Nil #

Pretty prints self into the given printer.


[View source]
def rchop(suffix : Char | String) : String #

Returns a new String with suffix removed from the end of the string.

"string".rchop('g')   # => "strin"
"string".rchop('x')   # => "string"
"string".rchop("ing") # => "str"
"string".rchop("inx") # => "string"

[View source]
def rchop : String #

Returns a new String with the last character removed. Applying rchop to an empty string returns an empty string.

"string\r\n".rchop # => "string\r"
"string\n\r".rchop # => "string\n"
"string\n".rchop   # => "string"
"string".rchop     # => "strin"
"x".rchop.rchop    # => ""

[View source]
def rchop?(suffix : Char | String) : String | Nil #

Returns a new String with suffix removed from the end of the string if possible, else returns nil.

"string".rchop?('g')   # => "strin"
"string".rchop?('x')   # => nil
"string".rchop?("ing") # => "str"
"string".rchop?("inx") # => nil

[View source]
def rchop? : String | Nil #

Returns a new String with the last character removed if possible, else returns nil.

"string\r\n".rchop? # => "string\r"
"string\n\r".rchop? # => "string\n"
"string\n".rchop?   # => "string"
"string".rchop?     # => "strin"
"".rchop?           # => nil

[View source]
def reverse : String #

Reverses the order of characters in the string.

"Argentina".reverse # => "anitnegrA"
"racecar".reverse   # => "racecar"

Works on Unicode graphemes (and not codepoints) so combining characters are preserved.

"Noe\u0308l".reverse # => "lëoN"

[View source]
def rindex(search : Char, offset = size - 1) #

Returns the index of the last appearance of search in the string, If offset is present, it defines the position to end the search (characters beyond this point are ignored).

"Hello, World".rindex('o')    # => 8
"Hello, World".rindex('Z')    # => nil
"Hello, World".rindex("o", 5) # => 4
"Hello, World".rindex("W", 2) # => nil

[View source]
def rindex(search : String, offset = size - search.size) : Int32 | Nil #

Returns the index of the last appearance of search in the string, If offset is present, it defines the position to end the search (characters beyond this point are ignored).

"Hello, World".rindex('o')    # => 8
"Hello, World".rindex('Z')    # => nil
"Hello, World".rindex("o", 5) # => 4
"Hello, World".rindex("W", 2) # => nil

[View source]
def rindex(search : Regex, offset = size, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Int32 | Nil #

Returns the index of the last appearance of search in the string, If offset is present, it defines the position to end the search (characters beyond this point are ignored).

"Hello, World".rindex('o')    # => 8
"Hello, World".rindex('Z')    # => nil
"Hello, World".rindex("o", 5) # => 4
"Hello, World".rindex("W", 2) # => nil

[View source]
def rindex!(search : String, offset = size - search.size) : Int32 #

Returns the index of the last appearance of search in the string, If offset is present, it defines the position to end the search (characters beyond this point are ignored).

"Hello, World".rindex('o')    # => 8
"Hello, World".rindex('Z')    # => nil
"Hello, World".rindex("o", 5) # => 4
"Hello, World".rindex("W", 2) # => nil

[View source]
def rindex!(search : Char, offset = size - 1) : Int32 #

Returns the index of the last appearance of search in the string, If offset is present, it defines the position to end the search (characters beyond this point are ignored).

"Hello, World".rindex('o')    # => 8
"Hello, World".rindex('Z')    # => nil
"Hello, World".rindex("o", 5) # => 4
"Hello, World".rindex("W", 2) # => nil

[View source]
def rindex!(search : Regex, offset = size, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Int32 #

Returns the index of the last appearance of search in the string, If offset is present, it defines the position to end the search (characters beyond this point are ignored).

"Hello, World".rindex('o')    # => 8
"Hello, World".rindex('Z')    # => nil
"Hello, World".rindex("o", 5) # => 4
"Hello, World".rindex("W", 2) # => nil

Raises Enumerable::NotFoundError if search does not occur in self.


[View source]
def rjust(len : Int, char : Char = ' ') : String #

Adds instances of char to left of the string until it is at least size of len.

"Purple".rjust(8)      # => "  Purple"
"Purple".rjust(8, '-') # => "--Purple"
"Aubergine".rjust(8)   # => "Aubergine"

[View source]
def rjust(io : IO, len : Int, char : Char = ' ') : Nil #

Adds instances of char to left of the string until it is at least size of len, and then appends the result to the given IO.

io = IO::Memory.new
"Purple".rjust(io, 8, '-')
io.to_s # => "--Purple"

[View source]
def rpartition(search : Char | String) : Tuple(String, String, String) #

Searches separator or pattern (Regex) in the string from the end of the string, and returns a Tuple with 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"}

[View source]
def rpartition(search : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Tuple(String, String, String) #

Searches separator or pattern (Regex) in the string from the end of the string, and returns a Tuple with 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"}

[View source]
def rstrip(char : Char) : String #

Returns a new string with trailing occurrences of char removed.

"aaabcdaaa".rstrip('a') # => "aaabcd"

[View source]
def rstrip(chars : String) : String #

Returns a new string where trailing occurrences of any char in chars are removed. The chars argument is not a suffix; rather; all combinations of its values are stripped.

"abcdefcba".rstrip("abc") # => "abcdef"

[View source]
def rstrip : String #

Returns a new String with trailing whitespace removed.

"    hello    ".rstrip # => "    hello"
"\tgoodbye\r\n".rstrip # => "\tgoodbye"

[View source]
def rstrip(&block : Char -> _) : String #

Returns a new string where trailing characters for which the block returns a truthy value are removed.

"bcadefcba".rstrip { |c| 'a' <= c <= 'c' } # => "bcadef"

[View source]
def scan(pattern : String, &) : self #

Searches the string for instances of pattern, yielding the matched string for each match.


[View source]
def scan(pattern : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None, &) : self #

Searches the string for instances of pattern, yielding a Regex::MatchData for each match.


[View source]
def scan(pattern : String) : Array(String) #

Searches the string for instances of pattern, returning an array of the matched string for each match.


[View source]
def scan(pattern : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Array(Regex::MatchData) #

Searches the string for instances of pattern, returning an Array of Regex::MatchData for each match.


[View source]
def scrub(replacement = Char::REPLACEMENT) : String #

Returns a String where bytes that are invalid in the UTF-8 encoding are replaced with replacement.


[View source]
def size : Int32 #

Returns the number of unicode codepoints in this string.

"hello".size # => 5
"你好".size    # => 2

[View source]
def split(limit : Int32 | Nil = nil) : Array(String) #

Makes an array by splitting the string on any amount of ASCII whitespace characters (and removing that whitespace).

If limit is present, up to limit new strings will be created, with the entire remainder added to the last string.

old_pond = "
  Old pond
  a frog leaps in
  water's sound
"
old_pond.split    # => ["Old", "pond", "a", "frog", "leaps", "in", "water's", "sound"]
old_pond.split(3) # => ["Old", "pond", "a frog leaps in\n  water's sound\n"]

[View source]
def split(limit : Int32 | Nil = nil, &block : String -> _) #

Splits the string after any amount of ASCII whitespace characters and yields each non-whitespace part to a block.

If limit is present, up to limit new strings will be created, with the entire remainder added to the last string.

ary = [] of String
old_pond = "
  Old pond
  a frog leaps in
  water's sound
"

old_pond.split { |s| ary << s }
ary # => ["Old", "pond", "a", "frog", "leaps", "in", "water's", "sound"]
ary.clear

old_pond.split(3) { |s| ary << s }
ary # => ["Old", "pond", "a frog leaps in\n  water's sound\n"]

[View source]
def split(separator : Char, limit = nil, *, remove_empty = false) : Array(String) #

Makes an Array by splitting the string on the given character separator (and removing that character).

If limit is present, up to limit new strings will be created, with the entire remainder added to the last string.

If remove_empty is true, any empty strings are removed from the result.

"foo,,bar,baz".split(',')                     # => ["foo", "", "bar", "baz"]
"foo,,bar,baz".split(',', remove_empty: true) # => ["foo", "bar", "baz"]
"foo,bar,baz".split(',', 2)                   # => ["foo", "bar,baz"]

[View source]
def split(separator : Char, limit = nil, *, remove_empty = false, &block : String -> _) #

Splits the string after each character separator and yields each part to a block.

If limit is present, up to limit new strings will be created, with the entire remainder added to the last string.

If remove_empty is true, any empty strings are not yielded.

ary = [] of String

"foo,,bar,baz".split(',') { |string| ary << string }
ary # => ["foo", "", "bar", "baz"]
ary.clear

"foo,,bar,baz".split(',', remove_empty: true) { |string| ary << string }
ary # => ["foo", "bar", "baz"]
ary.clear

"foo,bar,baz".split(',', 2) { |string| ary << string }
ary # => ["foo", "bar,baz"]

[View source]
def split(separator : String, limit = nil, *, remove_empty = false) : Array(String) #

Makes an Array by splitting the string on separator (and removing instances of separator).

If limit is present, the array will be limited to limit items and the final item will contain the remainder of the string.

If separator is an empty string (""), the string will be separated into one-character strings.

If remove_empty is true, any empty strings are removed from the result.

long_river_name = "Mississippi"
long_river_name.split("ss")                    # => ["Mi", "i", "ippi"]
long_river_name.split("i")                     # => ["M", "ss", "ss", "pp", ""]
long_river_name.split("i", remove_empty: true) # => ["M", "ss", "ss", "pp"]
long_river_name.split("")                      # => ["M", "i", "s", "s", "i", "s", "s", "i", "p", "p", "i"]

[View source]
def split(separator : String, limit = nil, *, remove_empty = false, &block : String -> _) #

Splits the string after each string separator and yields each part to a block.

If limit is present, the array will be limited to limit items and the final item will contain the remainder of the string.

If separator is an empty string (""), the string will be separated into one-character strings.

If remove_empty is true, any empty strings are removed from the result.

ary = [] of String
long_river_name = "Mississippi"

long_river_name.split("ss") { |s| ary << s }
ary # => ["Mi", "i", "ippi"]
ary.clear

long_river_name.split("i") { |s| ary << s }
ary # => ["M", "ss", "ss", "pp", ""]
ary.clear

long_river_name.split("i", remove_empty: true) { |s| ary << s }
ary # => ["M", "ss", "ss", "pp"]
ary.clear

long_river_name.split("") { |s| ary << s }
ary # => ["M", "i", "s", "s", "i", "s", "s", "i", "p", "p", "i"]

[View source]
def split(separator : Regex, limit = nil, *, remove_empty = false, options : Regex::MatchOptions = Regex::MatchOptions::None) : Array(String) #

Makes an Array by splitting the string on separator (and removing instances of separator).

If limit is present, the array will be limited to limit items and the final item will contain the remainder of the string.

If separator is an empty regex (//), the string will be separated into one-character strings.

If remove_empty is true, any empty strings are removed from the result.

long_river_name = "Mississippi"
long_river_name.split(/s+/) # => ["Mi", "i", "ippi"]
long_river_name.split(//)   # => ["M", "i", "s", "s", "i", "s", "s", "i", "p", "p", "i"]

[View source]
def split(separator : Regex, limit = nil, *, remove_empty = false, options : Regex::MatchOptions = Regex::MatchOptions::None, &block : String -> _) #

Splits the string after each regex separator and yields each part to a block.

If limit is present, the array will be limited to limit items and the final item will contain the remainder of the string.

If separator is an empty regex (//), the string will be separated into one-character strings.

If remove_empty is true, any empty strings are removed from the result.

ary = [] of String
long_river_name = "Mississippi"

long_river_name.split(/s+/) { |s| ary << s }
ary # => ["Mi", "i", "ippi"]
ary.clear

long_river_name.split(//) { |s| ary << s }
ary # => ["M", "i", "s", "s", "i", "s", "s", "i", "p", "p", "i"]

[View source]
def squeeze(&) : String #

Yields each char in this string to the block. Returns a new String, that has all characters removed, that were the same as the previous one and for which the given block returned a truthy value.

"aaabbbccc".squeeze &.in?('a', 'b') # => "abccc"
"aaabbbccc".squeeze &.in?('a', 'c') # => "abbbc"

[View source]
def squeeze(char : Char) : String #

Returns a new String, with all runs of char replaced by one instance.

"a    bbb".squeeze(' ') # => "a bbb"

[View source]
def squeeze : String #

Returns a new String, that has all characters removed, that were the same as the previous one.

"a       bbb".squeeze # => "a b"

[View source]
def squeeze(*sets : String) : String #

Sets should be a list of strings following the rules described at Char#in_set?. Returns a new String with all runs of the same character replaced by one instance, if they match the given set.

If no set is given, all characters are matched.

"aaabbbcccddd".squeeze("b-d") # => "aaabcd"
"a       bbb".squeeze         # => "a b"

[View source]
def starts_with?(str : String) : Bool #

Returns true if this string starts with the given str.

"hello".starts_with?("h")  # => true
"hello".starts_with?("he") # => true
"hello".starts_with?("hu") # => false

[View source]
def starts_with?(char : Char) : Bool #

Returns true if this string starts with the given char.

"hello".starts_with?('h') # => true
"hello".starts_with?('e') # => false

[View source]
def starts_with?(re : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : Bool #

Returns true if the regular expression re matches at the start of this string.

"22hello".starts_with?(/[0-9]/) # => true
"22hello".starts_with?(/[a-z]/) # => false
"h22".starts_with?(/[a-z]/)     # => true
"h22".starts_with?(/[A-Z]/)     # => false
"h22".starts_with?(/[a-z]{2}/)  # => false
"hh22".starts_with?(/[a-z]{2}/) # => true

[View source]
def strip(char : Char) : String #

Returns a new string where leading and trailing occurrences of char are removed.

"aaabcdaaa".strip('a') # => "bcd"

[View source]
def strip(chars : String) : String #

Returns a new string where leading and trailing occurrences of any char in chars are removed. The chars argument is not a prefix or suffix; rather; all combinations of its values are stripped.

"abcdefcba".strip("abc") # => "def"

[View source]
def strip : String #

Returns a new String with leading and trailing whitespace removed.

"    hello    ".strip # => "hello"
"\tgoodbye\r\n".strip # => "goodbye"

[View source]
def strip(&block : Char -> _) : String #

Returns a new string where leading and trailing characters for which the block returns a truthy value are removed.

"bcadefcba".strip { |c| 'a' <= c <= 'c' } # => "def"

[View source]
def sub(string : String, &) : String #

Returns a String where the first occurrences of the given string is replaced with the block's value.

"hello yellow".sub("ll") { "dd" } # => "heddo yellow"

[View source]
def sub(pattern : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None, &) : String #

Returns a String where the first occurrence of pattern is replaced by the block's return value.

"hello".sub(/./) { |s| s[0].ord.to_s + ' ' } # => "104 ello"

[View source]
def sub(&block : Char -> _) : String #

Returns a new String where the first character is yielded to the given block and replaced by its return value.

"hello".sub { |char| char + 1 } # => "iello"
"hello".sub { "hi" }            # => "hiello"

[View source]
def sub(char : Char, replacement) : String #

Returns a String where the first occurrence of char is replaced by replacement.

"hello".sub('l', "lo")      # => "helolo"
"hello world".sub('o', 'a') # => "hella world"

[View source]
def sub(pattern : Regex, hash : Hash(String, _) | NamedTuple, options : Regex::MatchOptions = Regex::MatchOptions::None) : String #

Returns a String where the first occurrences of the given pattern is replaced with the matching entry from the hash of replacements. If the first match is not included in the hash, nothing is replaced.

"hello".sub(/(he|l|o)/, {"he": "ha", "l": "la"}) # => "hallo"
"hello".sub(/(he|l|o)/, {"l": "la"})             # => "hello"

[View source]
def sub(string : String, replacement) : String #

Returns a String where the first occurrences of the given string is replaced with the given replacement.

"hello yellow".sub("ll", "dd") # => "heddo yellow"

[View source]
def sub(index : Int, replacement : Char) : String #

Returns a new String with the character at the given index replaced by replacement.

"hello".sub(1, 'a') # => "hallo"

[View source]
def sub(index : Int, replacement : String) : String #

Returns a new String with the character at the given index replaced by replacement.

"hello".sub(1, "eee") # => "heeello"

[View source]
def sub(range : Range, replacement : Char) : String #

Returns a new String with characters at the given range replaced by replacement.

"hello".sub(1..2, 'a') # => "halo"

[View source]
def sub(range : Range, replacement : String) : String #

Returns a new String with characters at the given range replaced by replacement.

"hello".sub(1..2, "eee") # => "heeelo"

[View source]
def sub(pattern : Regex, replacement, backreferences = true, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : String #

Returns a String where the first occurrence of pattern is replaced by replacement

"hello".sub(/[aeiou]/, "*") # => "h*llo"

Within replacement, the special match variable $~ will not refer to the current match.

If backreferences is true (the default value), replacement can include backreferences:

"hello".sub(/[aeiou]/, "(\\0)") # => "h(e)llo"

When substitution is performed, any backreferences found in replacement will be replaced with the contents of the corresponding capture group in pattern. Backreferences to capture groups that were not present in pattern or that did not match will be skipped. See Regex for information about capture groups.

Backreferences are expressed in the form "\\d", where d is a group number, or "\\k&lt;name>" where name is the name of a named capture group. A sequence of literal characters resembling a backreference can be expressed by placing "\\" before the sequence.

"foo".sub(/o/, "x\\0x")                  # => "fxoxo"
"foofoo".sub(/(?<bar>oo)/, "|\\k<bar>|") # => "f|oo|foo"
"foo".sub(/o/, "\\\\0")                  # => "f\\0o"

Raises ArgumentError if an incomplete named back-reference is present in replacement.

Raises IndexError if a named group referenced in replacement is not present in pattern.


[View source]
def sub(hash : Hash(Char, _)) : String #

Returns a String where the first char in the string matching a key in the given hash is replaced by the corresponding hash value.

"hello".sub({'a' => 'b', 'l' => 'd'}) # => "hedlo"

[View source]
def succ : String #

Returns the successor of the string. The successor is calculated by incrementing characters starting from the rightmost alphanumeric (or the rightmost character if there are no alphanumerics) in the string. Incrementing a digit always results in another digit, and incrementing a letter results in another letter of the same case.

If the increment generates a "carry", the character to the left of it is incremented. This process repeats until there is no carry, adding an additional character if necessary.

"abcd".succ      # => "abce"
"THX1138".succ   # => "THX1139"
"((koala))".succ # => "((koalb))"
"1999zzz".succ   # => "2000aaa"
"ZZZ9999".succ   # => "AAAA0000"
"***".succ       # => "**+"

[View source]
def titleize(io : IO, options : Unicode::CaseOptions = :none, *, underscore_to_space : Bool = false) : Nil #

Writes a titleized version of self to the given io. Optionally, if underscore_to_space is true, underscores (_) will be converted to a space and the following letter converted to uppercase.

io = IO::Memory.new
"x-men: the last stand".titleize io
io.to_s # => "X-men: The Last Stand"

[View source]
def titleize(options : Unicode::CaseOptions = :none, *, underscore_to_space : Bool = false) : String #

Returns a new String with the first letter after any space converted to uppercase and every other letter converted to lowercase. Optionally, if underscore_to_space is true, underscores (_) will be converted to a space and the following letter converted to uppercase.

"hEllO tAb\tworld".titleize                   # => "Hello Tab\tWorld"
"  spaces before".titleize                    # => "  Spaces Before"
"x-men: the last stand".titleize              # => "X-men: The Last Stand"
"foo_bar".titleize                            # => "Foo_bar"
"foo_bar".titleize(underscore_to_space: true) # => "Foo Bar"

[View source]
def to_big_d : BigDecimal #

Converts self to BigDecimal.

require "big"
"1212341515125412412412421".to_big_d

[View source]
def to_big_f : BigFloat #

Converts self to a BigFloat.

require "big"
"1234.0".to_big_f

[View source]
def to_big_i(base = 10) : BigInt #

Returns a BigInt from this string, in the given base.

Raises ArgumentError if this string doesn't denote a valid integer.

require "big"

"3a060dbf8d1a5ac3e67bc8f18843fc48".to_big_i(16)

[View source]
def to_f(whitespace : Bool = true, strict : Bool = true) : Float64 #

Returns the result of interpreting characters in this string as a floating point number (Float64). This method raises an exception if the string is not a valid float representation or exceeds the range of the data type. Values representing infinity or NaN are considered valid.

Options:

  • whitespace: if true, leading and trailing whitespaces are allowed
  • strict: if true, extraneous characters past the end of the number are disallowed
"123.45e1".to_f                # => 1234.5
"45.67 degrees".to_f           # raises ArgumentError
"thx1138".to_f(strict: false)  # raises ArgumentError
" 1.2".to_f(whitespace: false) # raises ArgumentError
"1.2foo".to_f(strict: false)   # => 1.2

[View source]
def to_f32(whitespace : Bool = true, strict : Bool = true) : Float32 #

Same as #to_f but returns a Float32.


[View source]
def to_f32?(whitespace : Bool = true, strict : Bool = true) : Float32 | Nil #

Same as #to_f? but returns a Float32.


[View source]
def to_f64(whitespace : Bool = true, strict : Bool = true) : Float64 #

Returns the result of interpreting characters in this string as a floating point number (Float64). This method raises an exception if the string is not a valid float representation or exceeds the range of the data type. Values representing infinity or NaN are considered valid.

Options:

  • whitespace: if true, leading and trailing whitespaces are allowed
  • strict: if true, extraneous characters past the end of the number are disallowed
"123.45e1".to_f                # => 1234.5
"45.67 degrees".to_f           # raises ArgumentError
"thx1138".to_f(strict: false)  # raises ArgumentError
" 1.2".to_f(whitespace: false) # raises ArgumentError
"1.2foo".to_f(strict: false)   # => 1.2

[View source]
def to_f64?(whitespace : Bool = true, strict : Bool = true) : Float64 | Nil #

Returns the result of interpreting characters in this string as a floating point number (Float64). This method returns nil if the string is not a valid float representation or exceeds the range of the data type. Values representing infinity or NaN are considered valid.

Options:

  • whitespace: if true, leading and trailing whitespaces are allowed
  • strict: if true, extraneous characters past the end of the number are disallowed
"123.45e1".to_f?                # => 1234.5
"45.67 degrees".to_f?           # => nil
"thx1138".to_f?                 # => nil
" 1.2".to_f?(whitespace: false) # => nil
"1.2foo".to_f?(strict: false)   # => 1.2

[View source]
def to_f?(whitespace : Bool = true, strict : Bool = true) : Float64 | Nil #

Returns the result of interpreting characters in this string as a floating point number (Float64). This method returns nil if the string is not a valid float representation or exceeds the range of the data type. Values representing infinity or NaN are considered valid.

Options:

  • whitespace: if true, leading and trailing whitespaces are allowed
  • strict: if true, extraneous characters past the end of the number are disallowed
"123.45e1".to_f?                # => 1234.5
"45.67 degrees".to_f?           # => nil
"thx1138".to_f?                 # => nil
" 1.2".to_f?(whitespace: false) # => nil
"1.2foo".to_f?(strict: false)   # => 1.2

[View source]
def to_i(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) #

Returns the result of interpreting leading characters in this string as an integer base base (between 2 and 36).

If there is not a valid number at the start of this string, or if the resulting integer doesn't fit an Int32, an ArgumentError is raised.

Options:

  • whitespace: if true, leading and trailing whitespaces are allowed
  • underscore: if true, underscores in numbers are allowed
  • prefix: if true, the prefixes "0x", "0o" and "0b" override the base
  • strict: if true, extraneous characters past the end of the number are disallowed
  • leading_zero_is_octal: if true, then a number prefixed with "0" will be treated as an octal
"12345".to_i             # => 12345
"0a".to_i                # raises ArgumentError
"hello".to_i             # raises ArgumentError
"0a".to_i(16)            # => 10
"1100101".to_i(2)        # => 101
"1100101".to_i(8)        # => 294977
"1100101".to_i(10)       # => 1100101
"1100101".to_i(base: 16) # => 17826049

"12_345".to_i                   # raises ArgumentError
"12_345".to_i(underscore: true) # => 12345

"  12345  ".to_i                    # => 12345
"  12345  ".to_i(whitespace: false) # raises ArgumentError

"0x123abc".to_i               # raises ArgumentError
"0x123abc".to_i(prefix: true) # => 1194684

"99 red balloons".to_i                # raises ArgumentError
"99 red balloons".to_i(strict: false) # => 99

"0755".to_i                              # => 755
"0755".to_i(leading_zero_is_octal: true) # => 493

[View source]
def to_i(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i, but returns the block's value if there is not a valid number at the start of this string, or if the resulting integer doesn't fit an Int32.

"12345".to_i { 0 } # => 12345
"hello".to_i { 0 } # => 0

[View source]
def to_i128(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int128 #

Same as #to_i but returns an Int128.


[View source]
def to_i128(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i but returns an Int128 or the block's value.


[View source]
def to_i128?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int128 | Nil #

Same as #to_i but returns an Int128 or nil.


[View source]
def to_i16(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int16 #

Same as #to_i but returns an Int16.


[View source]
def to_i16(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i but returns an Int16 or the block's value.


[View source]
def to_i16?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int16 | Nil #

Same as #to_i but returns an Int16 or nil.


[View source]
def to_i32(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int32 #

Same as #to_i.


[View source]
def to_i32(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i.


[View source]
def to_i32?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int32 | Nil #

Same as #to_i.


[View source]
def to_i64(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int64 #

Same as #to_i but returns an Int64.


[View source]
def to_i64(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i but returns an Int64 or the block's value.


[View source]
def to_i64?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int64 | Nil #

Same as #to_i but returns an Int64 or nil.


[View source]
def to_i8(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int8 #

Same as #to_i but returns an Int8.


[View source]
def to_i8(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i but returns an Int8 or the block's value.


[View source]
def to_i8?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : Int8 | Nil #

Same as #to_i but returns an Int8 or nil.


[View source]
def to_i?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) #

Same as #to_i, but returns nil if there is not a valid number at the start of this string, or if the resulting integer doesn't fit an Int32.

"12345".to_i?             # => 12345
"99 red balloons".to_i?   # => nil
"0a".to_i?(strict: false) # => 0
"hello".to_i?             # => nil

[View source]
def to_json(json : JSON::Builder) : Nil #

[View source]
def to_json_object_key : String #

[View source]
def to_s(io : IO) : Nil #

Appends self to io.


[View source]
def to_s : String #

Returns self.


[View source]
def to_slice : Bytes #

Returns the underlying bytes of this String.

The returned slice is read-only.

May contain invalid UTF-8 byte sequences; #scrub may be used to first obtain a String that is guaranteed to be valid UTF-8.


[View source]
def to_u128(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt128 #

Same as #to_i but returns an UInt128.


[View source]
def to_u128(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i but returns an UInt128 or the block's value.


[View source]
def to_u128?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt128 | Nil #

Same as #to_i but returns an UInt128 or nil.


[View source]
def to_u16(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt16 #

Same as #to_i but returns an UInt16.


[View source]
def to_u16(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i but returns an UInt16 or the block's value.


[View source]
def to_u16?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt16 | Nil #

Same as #to_i but returns an UInt16 or nil.


[View source]
def to_u32(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt32 #

Same as #to_i but returns an UInt32.


[View source]
def to_u32(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i but returns an UInt32 or the block's value.


[View source]
def to_u32?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt32 | Nil #

Same as #to_i but returns an UInt32 or nil.


[View source]
def to_u64(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt64 #

Same as #to_i but returns an UInt64.


[View source]
def to_u64(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i but returns an UInt64 or the block's value.


[View source]
def to_u64?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt64 | Nil #

Same as #to_i but returns an UInt64 or nil.


[View source]
def to_u8(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt8 #

Same as #to_i but returns an UInt8.


[View source]
def to_u8(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false, &) #

Same as #to_i but returns an UInt8 or the block's value.


[View source]
def to_u8?(base : Int = 10, whitespace : Bool = true, underscore : Bool = false, prefix : Bool = false, strict : Bool = true, leading_zero_is_octal : Bool = false) : UInt8 | Nil #

Same as #to_i but returns an UInt8 or nil.


[View source]
def to_unsafe : Pointer(UInt8) #

Returns a pointer to the underlying bytes of this String.

May contain invalid UTF-8 byte sequences; #scrub may be used to first obtain a String that is guaranteed to be valid UTF-8.


[View source]
def to_utf16 : Slice(UInt16) #

Returns the UTF-16 encoding of the given string.

Invalid chars (in the range U+D800..U+DFFF) are encoded with the unicode replacement char value 0xfffd.

The byte following the end of this slice (but not included in it) is defined to be zero. This allows passing the result of this function into C functions that expect a null-terminated UInt16*.

"hi 𐂥".to_utf16 # => Slice[104_u16, 105_u16, 32_u16, 55296_u16, 56485_u16]

[View source]
def to_yaml(yaml : YAML::Nodes::Builder) : Nil #

[View source]
def tr(from : String, to : String) : String #

Returns a new string _tr_anslating characters using from and to as a map. If to is shorter than from, the last character in to is used for the rest. If to is empty, this acts like String#delete.

"aabbcc".tr("abc", "xyz") # => "xxyyzz"
"aabbcc".tr("abc", "x")   # => "xxxxxx"
"aabbcc".tr("a", "xyz")   # => "xxbbcc"

[View source]
def underscore(options : Unicode::CaseOptions = :none) : String #

Converts camelcase boundaries to underscores.

"DoesWhatItSaysOnTheTin".underscore                         # => "does_what_it_says_on_the_tin"
"PartyInTheUSA".underscore                                  # => "party_in_the_usa"
"HTTP_CLIENT".underscore                                    # => "http_client"
"3.14IsPi".underscore                                       # => "3.14_is_pi"
"InterestingImage".underscore(Unicode::CaseOptions::Turkic) # => "ınteresting_ımage"

[View source]
def underscore(io : IO, options : Unicode::CaseOptions = :none) : Nil #

Writes an underscored version of self to the given io.

io = IO::Memory.new
"DoesWhatItSaysOnTheTin".underscore io
io.to_s # => "does_what_it_says_on_the_tin"

[View source]
def unicode_normalize(form : Unicode::NormalizationForm = :nfc) : String #

Returns the result of normalizing this String according to the given Unicode normalization form.

str = "\u{1E9B}\u{0323}"                # => "ẛ̣"
str.unicode_normalize.codepoints        # => [0x1E9B, 0x0323]
str.unicode_normalize(:nfd).codepoints  # => [0x017F, 0x0323, 0x0307]
str.unicode_normalize(:nfkc).codepoints # => [0x1E69]
str.unicode_normalize(:nfkd).codepoints # => [0x0073, 0x0323, 0x0307]

[View source]
def unicode_normalize(io : IO, form : Unicode::NormalizationForm = :nfc) : Nil #

Normalizes this String according to the given Unicode normalization form and writes the result to the given io.


[View source]
def unicode_normalized?(form : Unicode::NormalizationForm = :nfc) : Bool #

Returns whether this String is in the given Unicode normalization form.

foo = "\u{00E0}"              # => "à"
foo.unicode_normalized?       # => true
foo.unicode_normalized?(:nfd) # => false

bar = "\u{0061}\u{0300}"      # => "à"
bar.unicode_normalized?       # => false
bar.unicode_normalized?(:nfd) # => true

[View source]
def unsafe_byte_at(index : Int) : UInt8 #

Returns the byte at the given index without bounds checking.

DEPRECATED Use to_unsafe[index] instead.


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def unsafe_byte_slice(byte_offset, count) : Slice #

Returns count of underlying bytes of this String starting at given byte_offset.

The returned slice is read-only.


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def unsafe_byte_slice(byte_offset) : Slice #

Returns the underlying bytes of this String starting at given byte_offset.

The returned slice is read-only.


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def upcase(options : Unicode::CaseOptions = :none) : String #

Returns a new String with each lowercase letter replaced with its uppercase counterpart.

"hEllO".upcase # => "HELLO"

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def upcase(io : IO, options : Unicode::CaseOptions = :none) : Nil #

Writes a upcased version of self to the given io.

io = IO::Memory.new
"hEllO".upcase io
io.to_s # => "HELLO"

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def valid_encoding? : Bool #

Returns true if this String is encoded correctly according to the UTF-8 encoding.


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