Results for: "String#[]"

String

A String object has an arbitrary sequence of bytes, typically representing text or binary data. A String object may be created using String::new or as literals.

String objects differ from Symbol objects in that Symbol objects are designed to be used as identifiers, instead of text or data.

You can create a String object explicitly with:

You can convert certain objects to Strings with:

Some String methods modify self. Typically, a method whose name ends with ! modifies self and returns self; often a similarly named method (without the !) returns a new string.

In general, if there exist both bang and non-bang version of method, the bang! mutates and the non-bang! does not. However, a method without a bang can also mutate, such as String#replace.

Substitution Methods

These methods perform substitutions:

Each of these methods takes:

The examples in this section mostly use methods String#sub and String#gsub; the principles illustrated apply to all four substitution methods.

Argument pattern

Argument pattern is commonly a regular expression:

s = 'hello'
s.sub(/[aeiou]/, '*')# => "h*llo"
s.gsub(/[aeiou]/, '*') # => "h*ll*"
s.gsub(/[aeiou]/, '')# => "hll"
s.sub(/ell/, 'al')   # => "halo"
s.gsub(/xyzzy/, '*') # => "hello"
'THX1138'.gsub(/\d+/, '00') # => "THX00"

When pattern is a string, all its characters are treated as ordinary characters (not as regexp special characters):

'THX1138'.gsub('\d+', '00') # => "THX1138"

String replacement

If replacement is a string, that string will determine the replacing string that is to be substituted for the matched text.

Each of the examples above uses a simple string as the replacing string.

String replacement may contain back-references to the pattern’s captures:

See Regexp for details.

Note that within the string replacement, a character combination such as $& is treated as ordinary text, and not as a special match variable. However, you may refer to some special match variables using these combinations:

See Regexp for details.

Note that \\ is interpreted as an escape, i.e., a single backslash.

Note also that a string literal consumes backslashes. See string literal for details about string literals.

A back-reference is typically preceded by an additional backslash. For example, if you want to write a back-reference \& in replacement with a double-quoted string literal, you need to write "..\\&..".

If you want to write a non-back-reference string \& in replacement, you need first to escape the backslash to prevent this method from interpreting it as a back-reference, and then you need to escape the backslashes again to prevent a string literal from consuming them: "..\\\\&..".

You may want to use the block form to avoid a lot of backslashes.

Hash replacement

If argument replacement is a hash, and pattern matches one of its keys, the replacing string is the value for that key:

h = {'foo' => 'bar', 'baz' => 'bat'}
'food'.sub('foo', h) # => "bard"

Note that a symbol key does not match:

h = {foo: 'bar', baz: 'bat'}
'food'.sub('foo', h) # => "d"

Block

In the block form, the current match string is passed to the block; the block’s return value becomes the replacing string:

 s = '@'
'1234'.gsub(/\d/) {|match| s.succ! } # => "ABCD"

Special match variables such as $1, $2, $`, $&, and $' are set appropriately.

Whitespace in Strings

In class String, whitespace is defined as a contiguous sequence of characters consisting of any mixture of the following:

Whitespace is relevant for these methods:

String Slices

A slice of a string is a substring that is selected by certain criteria.

These instance methods make use of slicing:

Each of the above methods takes arguments that determine the slice to be copied or replaced.

The arguments have several forms. For string string, the forms are:

string[index]

When non-negative integer argument index is given, the slice is the 1-character substring found in self at character offset index:

'bar'[0]       # => "b"
'bar'[2]       # => "r"
'bar'[20]      # => nil
'тест'[2]      # => "с"
'こんにちは'[4]  # => "は"

When negative integer index is given, the slice begins at the offset given by counting backward from the end of self:

'bar'[-3]         # => "b"
'bar'[-1]         # => "r"
'bar'[-20]        # => nil

string[start, length]

When non-negative integer arguments start and length are given, the slice begins at character offset start, if it exists, and continues for length characters, if available:

'foo'[0, 2]       # => "fo"
'тест'[1, 2]      # => "ес"
'こんにちは'[2, 2]  # => "にち"
# Zero length.
'foo'[2, 0]       # => ""
# Length not entirely available.
'foo'[1, 200]     # => "oo"
# Start out of range.
'foo'[4, 2]      # => nil

Special case: if start is equal to the length of self, the slice is a new empty string:

'foo'[3, 2]   # => ""
'foo'[3, 200] # => ""

When negative start and non-negative length are given, the slice beginning is determined by counting backward from the end of self, and the slice continues for length characters, if available:

'foo'[-2, 2]    # => "oo"
'foo'[-2, 200]  # => "oo"
# Start out of range.
'foo'[-4, 2]     # => nil

When negative length is given, there is no slice:

'foo'[1, -1]  # => nil
'foo'[-2, -1] # => nil

string[range]

When Range argument range is given, creates a substring of string using the indices in range. The slice is then determined as above:

'foo'[0..1]    # => "fo"
'foo'[0, 2]    # => "fo"

'foo'[2...2]   # => ""
'foo'[2, 0]    # => ""

'foo'[1..200]  # => "oo"
'foo'[1, 200]  # => "oo"

'foo'[4..5]    # => nil
'foo'[4, 2]    # => nil

'foo'[-4..-3]  # => nil
'foo'[-4, 2]   # => nil

'foo'[3..4]    # => ""
'foo'[3, 2]    # => ""

'foo'[-2..-1]  # => "oo"
'foo'[-2, 2]   # => "oo"

'foo'[-2..197] # => "oo"
'foo'[-2, 200] # => "oo"

string[regexp, capture = 0]

When the Regexp argument regexp is given, and the capture argument is 0, the slice is the first matching substring found in self:

'foo'[/o/] # => "o"
'foo'[/x/] # => nil
s = 'hello there'
s[/[aeiou](.)\1/] # => "ell"
s[/[aeiou](.)\1/, 0] # => "ell"

If argument capture is given and not 0, it should be either an capture group index (integer) or a capture group name (string or symbol); the slice is the specified capture (see Groups and Captures at Regexp):

s = 'hello there'
s[/[aeiou](.)\1/, 1] # => "l"
s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, "non_vowel"] # => "l"
s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, :vowel] # => "e"

If an invalid capture group index is given, there is no slice. If an invalid capture group name is given, IndexError is raised.

string[substring]

When the single String argument substring is given, returns the substring from self if found, otherwise nil:

'foo'['oo'] # => "oo"
'foo'['xx'] # => nil

What’s Here

First, what’s elsewhere. Class String:

Here, class String provides methods that are useful for:

Methods for Creating a String

Methods for a Frozen/Unfrozen String

Methods for Querying

Counts

Substrings

Encodings

Other

Methods for Comparing

Methods for Modifying a String

Each of these methods modifies self.

Insertion

Substitution

Casing

Encoding

Deletion

Methods for Converting to New String

Each of these methods returns a new String based on self, often just a modified copy of self.

Extension

Encoding

Substitution

Casing

Deletion

Duplication

Methods for Converting to Non-String

Each of these methods converts the contents of self to a non-String.

Characters, Bytes, and Clusters

Splitting

Matching

Numerics

Strings and Symbols

Methods for Iterating

String#[]

Returns the substring of self specified by the arguments. See examples at String Slices.

Gem::SafeMarshal::Elements::String

No documentation available

Array::[]

Returns a new array populated with the given objects.

Array.[]( 1, 'a', /^A/)  # => [1, "a", /^A/]
Array[ 1, 'a', /^A/ ]    # => [1, "a", /^A/]
[ 1, 'a', /^A/ ]         # => [1, "a", /^A/]

Array#[]

Returns elements from self; does not modify self.

When a single Integer argument index is given, returns the element at offset index:

a = [:foo, 'bar', 2]
a[0] # => :foo
a[2] # => 2
a # => [:foo, "bar", 2]

If index is negative, counts relative to the end of self:

a = [:foo, 'bar', 2]
a[-1] # => 2
a[-2] # => "bar"

If index is out of range, returns nil.

When two Integer arguments start and length are given, returns a new Array of size length containing successive elements beginning at offset start:

a = [:foo, 'bar', 2]
a[0, 2] # => [:foo, "bar"]
a[1, 2] # => ["bar", 2]

If start + length is greater than self.length, returns all elements from offset start to the end:

a = [:foo, 'bar', 2]
a[0, 4] # => [:foo, "bar", 2]
a[1, 3] # => ["bar", 2]
a[2, 2] # => [2]

If start == self.size and length >= 0, returns a new empty Array.

If length is negative, returns nil.

When a single Range argument range is given, treats range.min as start above and range.size as length above:

a = [:foo, 'bar', 2]
a[0..1] # => [:foo, "bar"]
a[1..2] # => ["bar", 2]

Special case: If range.start == a.size, returns a new empty Array.

If range.end is negative, calculates the end index from the end:

a = [:foo, 'bar', 2]
a[0..-1] # => [:foo, "bar", 2]
a[0..-2] # => [:foo, "bar"]
a[0..-3] # => [:foo]

If range.start is negative, calculates the start index from the end:

a = [:foo, 'bar', 2]
a[-1..2] # => [2]
a[-2..2] # => ["bar", 2]
a[-3..2] # => [:foo, "bar", 2]

If range.start is larger than the array size, returns nil.

a = [:foo, 'bar', 2]
a[4..1] # => nil
a[4..0] # => nil
a[4..-1] # => nil

When a single Enumerator::ArithmeticSequence argument aseq is given, returns an Array of elements corresponding to the indexes produced by the sequence.

a = ['--', 'data1', '--', 'data2', '--', 'data3']
a[(1..).step(2)] # => ["data1", "data2", "data3"]

Unlike slicing with range, if the start or the end of the arithmetic sequence is larger than array size, throws RangeError.

a = ['--', 'data1', '--', 'data2', '--', 'data3']
a[(1..11).step(2)]
# RangeError (((1..11).step(2)) out of range)
a[(7..).step(2)]
# RangeError (((7..).step(2)) out of range)

If given a single argument, and its type is not one of the listed, tries to convert it to Integer, and raises if it is impossible:

a = [:foo, 'bar', 2]
# Raises TypeError (no implicit conversion of Symbol into Integer):
a[:foo]

Integer#[]

Returns a slice of bits from self.

With argument offset, returns the bit at the given offset, where offset 0 refers to the least significant bit:

n = 0b10 # => 2
n[0]     # => 0
n[1]     # => 1
n[2]     # => 0
n[3]     # => 0

In principle, n[i] is equivalent to (n >> i) & 1. Thus, negative index always returns zero:

255[-1] # => 0

With arguments offset and size, returns size bits from self, beginning at offset and including bits of greater significance:

n = 0b111000       # => 56
"%010b" % n[0, 10] # => "0000111000"
"%010b" % n[4, 10] # => "0000000011"

With argument range, returns range.size bits from self, beginning at range.begin and including bits of greater significance:

n = 0b111000      # => 56
"%010b" % n[0..9] # => "0000111000"
"%010b" % n[4..9] # => "0000000011"

Raises an exception if the slice cannot be constructed.

Fiber::[]

Returns the value of the fiber storage variable identified by key.

The key must be a symbol, and the value is set by Fiber#[]= or Fiber#store.

See also Fiber::[]=.

Continuation#[]

Invokes the continuation. The program continues from the end of the callcc block. If no arguments are given, the original callcc returns nil. If one argument is given, callcc returns it. Otherwise, an array containing args is returned.

callcc {|cont|  cont.call }           #=> nil
callcc {|cont|  cont.call 1 }         #=> 1
callcc {|cont|  cont.call 1, 2, 3 }   #=> [1, 2, 3]

Dir::[]

Calls Dir.glob with argument patterns and the values of keyword arguments base and sort; returns the array of selected entry names.

OpenStruct#[]

Returns the value of an attribute, or nil if there is no such attribute.

require "ostruct"
person = OpenStruct.new("name" => "John Smith", "age" => 70)
person[:age]   # => 70, same as person.age

Set::[]

Creates a new set containing the given objects.

Set[1, 2]                   # => #<Set: {1, 2}>
Set[1, 2, 1]                # => #<Set: {1, 2}>
Set[1, 'c', :s]             # => #<Set: {1, "c", :s}>

Struct#[]

Returns a value from self.

With symbol or string argument name given, returns the value for the named member:

Customer = Struct.new(:name, :address, :zip)
joe = Customer.new("Joe Smith", "123 Maple, Anytown NC", 12345)
joe[:zip] # => 12345

Raises NameError if name is not the name of a member.

With integer argument n given, returns self.values[n] if n is in range; see Array Indexes at Array:

joe[2]  # => 12345
joe[-2] # => "123 Maple, Anytown NC"

Raises IndexError if n is out of range.

Symbol#[]

Equivalent to symbol.to_s[]; see String#[].

StringScanner#[]

Returns the n-th subgroup in the most recent match.

s = StringScanner.new("Fri Dec 12 1975 14:39")
s.scan(/(\w+) (\w+) (\d+) /)       # -> "Fri Dec 12 "
s[0]                               # -> "Fri Dec 12 "
s[1]                               # -> "Fri"
s[2]                               # -> "Dec"
s[3]                               # -> "12"
s.post_match                       # -> "1975 14:39"
s.pre_match                        # -> ""

s.reset
s.scan(/(?<wday>\w+) (?<month>\w+) (?<day>\d+) /)       # -> "Fri Dec 12 "
s[0]                               # -> "Fri Dec 12 "
s[1]                               # -> "Fri"
s[2]                               # -> "Dec"
s[3]                               # -> "12"
s[:wday]                           # -> "Fri"
s[:month]                          # -> "Dec"
s[:day]                            # -> "12"
s.post_match                       # -> "1975 14:39"
s.pre_match                        # -> ""

WIN32OLE#[]

Returns the value of Collection specified by a1, a2,.…

dict = WIN32OLE.new('Scripting.Dictionary')
dict.add('ruby', 'Ruby')
puts dict['ruby'] # => 'Ruby' (same as `puts dict.item('ruby')')

Remark: You can not use this method to get the property.

excel = WIN32OLE.new('Excel.Application')
# puts excel['Visible']  This is error !!!
puts excel.Visible # You should to use this style to get the property.

OLEProperty#[]

No documentation available

Hash::[]

Returns a new Hash object populated with the given objects, if any. See Hash::new.

With no argument, returns a new empty Hash.

When the single given argument is a Hash, returns a new Hash populated with the entries from the given Hash, excluding the default value or proc.

h = {foo: 0, bar: 1, baz: 2}
Hash[h] # => {:foo=>0, :bar=>1, :baz=>2}

When the single given argument is an Array of 2-element Arrays, returns a new Hash object wherein each 2-element array forms a key-value entry:

Hash[ [ [:foo, 0], [:bar, 1] ] ] # => {:foo=>0, :bar=>1}

When the argument count is an even number; returns a new Hash object wherein each successive pair of arguments has become a key-value entry:

Hash[:foo, 0, :bar, 1] # => {:foo=>0, :bar=>1}

Raises an exception if the argument list does not conform to any of the above.

Hash#[]

Returns the value associated with the given key, if found:

h = {foo: 0, bar: 1, baz: 2}
h[:foo] # => 0

If key is not found, returns a default value (see Default Values):

h = {foo: 0, bar: 1, baz: 2}
h[:nosuch] # => nil

ENV::[]

Returns the value for the environment variable name if it exists:

ENV['foo'] = '0'
ENV['foo'] # => "0"

Returns nil if the named variable does not exist.

Raises an exception if name is invalid. See Invalid Names and Values.

MatchData#[]

When arguments index, +start and length, or range are given, returns match and captures in the style of Array#[]:

m = /(.)(.)(\d+)(\d)/.match("THX1138.")
# => #<MatchData "HX1138" 1:"H" 2:"X" 3:"113" 4:"8">
m[0] # => "HX1138"
m[1, 2]  # => ["H", "X"]
m[1..3]  # => ["H", "X", "113"]
m[-3, 2] # => ["X", "113"]

When string or symbol argument name is given, returns the matched substring for the given name:

m = /(?<foo>.)(.)(?<bar>.+)/.match("hoge")
# => #<MatchData "hoge" foo:"h" bar:"ge">
m['foo'] # => "h"
m[:bar]  # => "ge"

If multiple captures have the same name, returns the last matched substring.

m = /(?<foo>.)(?<foo>.+)/.match("hoge")
# => #<MatchData "hoge" foo:"h" foo:"oge">
m[:foo] #=> "oge"

m = /\W(?<foo>.+)|\w(?<foo>.+)|(?<foo>.+)/.match("hoge")
#<MatchData "hoge" foo:nil foo:"oge" foo:nil>
m[:foo] #=> "oge"

PStore#[]

Returns the value for the given key if the key exists. nil otherwise; if not nil, the returned value is an object or a hierarchy of objects:

example_store do |store|
  store.transaction do
    store[:foo]  # => 0
    store[:nope] # => nil
  end
end

Returns nil if there is no such key.

See also Hierarchical Values.

Raises an exception if called outside a transaction block.

Proc#[]

Invokes the block, setting the block’s parameters to the values in params using something close to method calling semantics. Returns the value of the last expression evaluated in the block.

a_proc = Proc.new {|scalar, *values| values.map {|value| value*scalar } }
a_proc.call(9, 1, 2, 3)    #=> [9, 18, 27]
a_proc[9, 1, 2, 3]         #=> [9, 18, 27]
a_proc.(9, 1, 2, 3)        #=> [9, 18, 27]
a_proc.yield(9, 1, 2, 3)   #=> [9, 18, 27]

Note that prc.() invokes prc.call() with the parameters given. It’s syntactic sugar to hide “call”.

For procs created using lambda or ->() an error is generated if the wrong number of parameters are passed to the proc. For procs created using Proc.new or Kernel.proc, extra parameters are silently discarded and missing parameters are set to nil.

a_proc = proc {|a,b| [a,b] }
a_proc.call(1)   #=> [1, nil]

a_proc = lambda {|a,b| [a,b] }
a_proc.call(1)   # ArgumentError: wrong number of arguments (given 1, expected 2)

See also Proc#lambda?.

Method#[]

Invokes the meth with the specified arguments, returning the method’s return value.

m = 12.method("+")
m.call(3)    #=> 15
m.call(20)   #=> 32

Ractor#[]

get a value from ractor-local storage

Thread#[]

Attribute Reference—Returns the value of a fiber-local variable (current thread’s root fiber if not explicitly inside a Fiber), using either a symbol or a string name. If the specified variable does not exist, returns nil.

[
  Thread.new { Thread.current["name"] = "A" },
  Thread.new { Thread.current[:name]  = "B" },
  Thread.new { Thread.current["name"] = "C" }
].each do |th|
  th.join
  puts "#{th.inspect}: #{th[:name]}"
end

This will produce:

#<Thread:0x00000002a54220 dead>: A
#<Thread:0x00000002a541a8 dead>: B
#<Thread:0x00000002a54130 dead>: C

Thread#[] and Thread#[]= are not thread-local but fiber-local. This confusion did not exist in Ruby 1.8 because fibers are only available since Ruby 1.9. Ruby 1.9 chooses that the methods behaves fiber-local to save following idiom for dynamic scope.

def meth(newvalue)
  begin
    oldvalue = Thread.current[:name]
    Thread.current[:name] = newvalue
    yield
  ensure
    Thread.current[:name] = oldvalue
  end
end

The idiom may not work as dynamic scope if the methods are thread-local and a given block switches fiber.

f = Fiber.new {
  meth(1) {
    Fiber.yield
  }
}
meth(2) {
  f.resume
}
f.resume
p Thread.current[:name]
#=> nil if fiber-local
#=> 2 if thread-local (The value 2 is leaked to outside of meth method.)

For thread-local variables, please see thread_variable_get and thread_variable_set.

Next
Search took: 11ms  ·  Total Results: 3744