Class

Symbol objects represent named identifiers inside the Ruby interpreter.

You can create a Symbol object explicitly with:

  • A symbol literal.

The same Symbol object will be created for a given name or string for the duration of a program’s execution, regardless of the context or meaning of that name. Thus if Fred is a constant in one context, a method in another, and a class in a third, the Symbol :Fred will be the same object in all three contexts.

module One
  class Fred
  end
  $f1 = :Fred
end
module Two
  Fred = 1
  $f2 = :Fred
end
def Fred()
end
$f3 = :Fred
$f1.object_id   #=> 2514190
$f2.object_id   #=> 2514190
$f3.object_id   #=> 2514190

Constant, method, and variable names are returned as symbols:

module One
  Two = 2
  def three; 3 end
  @four = 4
  @@five = 5
  $six = 6
end
seven = 7

One.constants
# => [:Two]
One.instance_methods(true)
# => [:three]
One.instance_variables
# => [:@four]
One.class_variables
# => [:@@five]
global_variables.grep(/six/)
# => [:$six]
local_variables
# => [:seven]

Symbol objects are different from String objects in that Symbol objects represent identifiers, while String objects represent text or data.

What’s Here

First, what’s elsewhere. Class Symbol:

Here, class Symbol provides methods that are useful for:

Methods for Querying

  • ::all_symbols: Returns an array of the symbols currently in Ruby’s symbol table.

  • #=~: Returns the index of the first substring in symbol that matches a given Regexp or other object; returns nil if no match is found.

  • [], slice : Returns a substring of symbol determined by a given index, start/length, or range, or string.

  • empty?: Returns true if self.length is zero; false otherwise.

  • encoding: Returns the Encoding object that represents the encoding of symbol.

  • end_with?: Returns true if symbol ends with any of the given strings.

  • match: Returns a MatchData object if symbol matches a given Regexp; nil otherwise.

  • match?: Returns true if symbol matches a given Regexp; false otherwise.

  • length, size: Returns the number of characters in symbol.

  • start_with?: Returns true if symbol starts with any of the given strings.

Methods for Comparing

  • #<=>: Returns -1, 0, or 1 as a given symbol is smaller than, equal to, or larger than symbol.

  • ==, ===: Returns true if a given symbol has the same content and encoding.

  • casecmp: Ignoring case, returns -1, 0, or 1 as a given symbol is smaller than, equal to, or larger than symbol.

  • casecmp?: Returns true if symbol is equal to a given symbol after Unicode case folding; false otherwise.

Methods for Converting

  • capitalize: Returns symbol with the first character upcased and all other characters downcased.

  • downcase: Returns symbol with all characters downcased.

  • inspect: Returns the string representation of self as a symbol literal.

  • name: Returns the frozen string corresponding to symbol.

  • succ, next: Returns the symbol that is the successor to symbol.

  • swapcase: Returns symbol with all upcase characters downcased and all downcase characters upcased.

  • to_proc: Returns a Proc object which responds to the method named by symbol.

  • to_s, id2name: Returns the string corresponding to self.

  • to_sym, intern: Returns self.

  • upcase: Returns symbol with all characters upcased.

Class Methods

Returns an array of all symbols currently in Ruby’s symbol table:

Symbol.all_symbols.size    # => 9334
Symbol.all_symbols.take(3) # => [:!, :"\"", :"#"]

Deserializes JSON string by converting the string value stored in the object to a Symbol

Instance Methods

If object is a symbol, returns the equivalent of symbol.to_s <=> object.to_s:

:bar <=> :foo # => -1
:foo <=> :foo # => 0
:foo <=> :bar # => 1

Otherwise, returns nil:

:foo <=> 'bar' # => nil

Related: String#<=>.

Returns true if object is the same object as self, false otherwise.

Symbol#=== is an alias for Symbol#==.

An alias for ==

Equivalent to symbol.to_s =~ object, including possible updates to global variables; see String#=~.

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

Returns a hash, that will be turned into a JSON object and represent this object.

Equivalent to sym.to_s.capitalize.to_sym.

See String#capitalize.

Like Symbol#<=>, but case-insensitive; equivalent to self.to_s.casecmp(object.to_s):

lower = :abc
upper = :ABC
upper.casecmp(lower) # => 0
lower.casecmp(lower) # => 0
lower.casecmp(upper) # => 0

Returns nil if self and object have incompatible encodings, or if object is not a symbol:

sym = 'äöü'.encode("ISO-8859-1").to_sym
other_sym = 'ÄÖÜ'
sym.casecmp(other_sym) # => nil
:foo.casecmp(2)        # => nil

Unlike Symbol#casecmp?, case-insensitivity does not work for characters outside of ‘A’..‘Z’ and ‘a’..‘z’:

lower = :äöü
upper = :ÄÖÜ
upper.casecmp(lower) # => -1
lower.casecmp(lower) # => 0
lower.casecmp(upper) # => 1

Related: Symbol#casecmp?, String#casecmp.

Returns true if self and object are equal after Unicode case folding, otherwise false:

lower = :abc
upper = :ABC
upper.casecmp?(lower) # => true
lower.casecmp?(lower) # => true
lower.casecmp?(upper) # => true

Returns nil if self and object have incompatible encodings, or if object is not a symbol:

sym = 'äöü'.encode("ISO-8859-1").to_sym
other_sym = 'ÄÖÜ'
sym.casecmp?(other_sym) # => nil
:foo.casecmp?(2)        # => nil

Unlike Symbol#casecmp, works for characters outside of ‘A’..‘Z’ and ‘a’..‘z’:

lower = :äöü
upper = :ÄÖÜ
upper.casecmp?(lower) # => true
lower.casecmp?(lower) # => true
lower.casecmp?(upper) # => true

Related: Symbol#casecmp, String#casecmp?.

Equivalent to sym.to_s.downcase.to_sym.

See String#downcase.

Related: Symbol#upcase.

Returns true if self is :'', false otherwise.

Equivalent to self.to_s.encoding; see String#encoding.

Equivalent to self.to_s.end_with?; see String#end_with?.

An alias for to_s

Returns a string representation of self (including the leading colon):

:foo.inspect # => ":foo"

Related: Symbol#to_s, Symbol#name.

Returns self.

Symbol#intern is an alias for Symbol#to_sym.

Related: String#to_sym.

Equivalent to self.to_s.length; see String#length.

Symbol#size is an alias for Symbol#length.

Equivalent to self.to_s.match, including possible updates to global variables; see String#match.

Equivalent to sym.to_s.match?; see String#match.

Returns a frozen string representation of self (not including the leading colon):

:foo.name         # => "foo"
:foo.name.frozen? # => true

Related: Symbol#to_s, Symbol#inspect.

An alias for succ
An alias for length
An alias for []

Equivalent to self.to_s.start_with?; see String#start_with?.

Equivalent to self.to_s.succ.to_sym:

:foo.succ # => :fop

Symbol#next is an alias for Symbol#succ.

Related: String#succ.

Equivalent to sym.to_s.swapcase.to_sym.

See String#swapcase.

Stores class name (Symbol) with String representation of Symbol as a JSON string.

Returns a Proc object which calls the method with name of self on the first parameter and passes the remaining parameters to the method.

proc = :to_s.to_proc   # => #<Proc:0x000001afe0e48680(&:to_s) (lambda)>
proc.call(1000)        # => "1000"
proc.call(1000, 16)    # => "3e8"
(1..3).collect(&:to_s) # => ["1", "2", "3"]

Returns a string representation of self (not including the leading colon):

:foo.to_s # => "foo"

Symbol#id2name is an alias for Symbol#to_s.

Related: Symbol#inspect, Symbol#name.

Equivalent to sym.to_s.upcase.to_sym.

See String#upcase.