Class

Symbol objects represent named identifiers inside the Ruby interpreter.

You can create a Symbol object explicitly with:

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 the symbols currently in Ruby's symbol table.

Symbol.all_symbols.size    #=> 903
Symbol.all_symbols[1,20]   #=> [:floor, :ARGV, :Binding, :symlink,
                                :chown, :EOFError, :$;, :String,
                                :LOCK_SH, :"setuid?", :$<,
                                :default_proc, :compact, :extend,
                                :Tms, :getwd, :$=, :ThreadGroup,
                                :wait2, :$>]

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

Instance Methods


Compares symbol with other_symbol after calling to_s on each of the symbols. Returns -1, 0, +1, or nil depending on whether symbol is less than, equal to, or greater than other_symbol.

nil is returned if the two values are incomparable.

See String#<=> for more information.

Equality—If sym and obj are exactly the same symbol, returns true.

An alias for ==

Returns sym.to_s =~ obj.

Returns sym.to_s[].

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.

Case-insensitive version of Symbol#<=>:

:aBcDeF.casecmp(:abcde)   # => 1
:aBcDeF.casecmp(:abcdef)  # => 0
:aBcDeF.casecmp(:abcdefg) # => -1
:abcdef.casecmp(:ABCDEF)  # => 0

Returns nil if the two symbols have incompatible encodings, or if other_symbol is not a symbol:

sym = "\u{e4 f6 fc}".encode("ISO-8859-1").to_sym
other_sym = :"\u{c4 d6 dc}"
sym.casecmp(other_sym) # => nil
:foo.casecmp(2)        # => nil

Currently, case-insensitivity only works on characters A-Z/a-z, not all of Unicode. This is different from Symbol#casecmp?.

Related: Symbol#casecmp?.

Returns true if sym and other_symbol are equal after Unicode case folding, false if they are not equal:

:aBcDeF.casecmp?(:abcde)                  # => false
:aBcDeF.casecmp?(:abcdef)                 # => true
:aBcDeF.casecmp?(:abcdefg)                # => false
:abcdef.casecmp?(:ABCDEF)                 # => true
:"\u{e4 f6 fc}".casecmp?(:"\u{c4 d6 dc}") #=> true

Returns nil if the two symbols have incompatible encodings, or if other_symbol is not a symbol:

sym = "\u{e4 f6 fc}".encode("ISO-8859-1").to_sym
other_sym = :"\u{c4 d6 dc}"
sym.casecmp?(other_sym) # => nil
:foo.casecmp?(2)        # => nil

See Case Mapping.

Related: Symbol#casecmp.

Equivalent to sym.to_s.downcase.to_sym.

See String#downcase.

Related: Symbol#upcase.

Returns whether sym is :“” or not.

Returns the Encoding object that represents the encoding of sym.

Returns true if sym ends with one of the suffixes given.

:hello.end_with?("ello")               #=> true

# returns true if one of the +suffixes+ matches.
:hello.end_with?("heaven", "ello")     #=> true
:hello.end_with?("heaven", "paradise") #=> false

Returns the representation of sym as a symbol literal.

:fred.inspect   #=> ":fred"

In general, to_sym returns the Symbol corresponding to an object. As sym is already a symbol, self is returned in this case.

Same as sym.to_s.length.

Returns sym.to_s.match.

Returns sym.to_s.match?.

Returns the name or string corresponding to sym. Unlike to_s, the returned string is frozen.

:fred.name         #=> "fred"
:fred.name.frozen? #=> true
:fred.to_s         #=> "fred"
:fred.to_s.frozen? #=> false
An alias for succ

Returns true if sym starts with one of the prefixes given. Each of the prefixes should be a String or a Regexp.

:hello.start_with?("hell")               #=> true
:hello.start_with?(/H/i)                 #=> true

# returns true if one of the prefixes matches.
:hello.start_with?("heaven", "hell")     #=> true
:hello.start_with?("heaven", "paradise") #=> false

Same as sym.to_s.succ.intern.

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 responds to the given method by sym.

(1..3).collect(&:to_s)  #=> ["1", "2", "3"]

Returns the name or string corresponding to sym.

:fred.id2name   #=> "fred"
:ginger.to_s    #=> "ginger"

Note that this string is not frozen (unlike the symbol itself). To get a frozen string, use name.

Equivalent to sym.to_s.upcase.to_sym.

See String#upcase.