Class: Symbol

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Instance Chain: self, `::Comparable`
Inherits:	Object
Defined in:	string.c, proc.c, string.c, symbol.rb

Overview

A Symbol object represents a named identifier 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]

A Symbol object differs from a ::String object in that a Symbol object represents an identifier, while a ::String object represents text or data.

What’s Here

First, what’s elsewhere. Class Symbol:

Inherits from class Object.
Includes module Comparable.

Here, class Symbol provides methods that are useful for:

Querying
Comparing
Converting

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 Method Summary

.all_symbols ⇒ Symbol

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

Instance Attribute Summary

#empty? ⇒ Boolean readonly

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

Instance Method Summary

#<=>(object) ⇒ 1, ...

If object is a symbol, returns the equivalent of symbol.to_s <=> object.to_s:
#==
#===
#=~(object) ⇒ Integer^?

Equivalent to symbol.to_s =~ object, including possible updates to global variables; see String#=~.
#[](index) ⇒ String^? (also: #slice)

Equivalent to symbol.to_s[]; see String#[].
#capitalize(*options) ⇒ Symbol

Equivalent to sym.to_s.capitalize.to_sym.
#casecmp(object) ⇒ 1, ...

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

Returns true if self and object are equal after Unicode case folding, otherwise false:
#downcase(*options) ⇒ Symbol

Equivalent to sym.to_s.downcase.to_sym.
#encoding ⇒ Encoding

Equivalent to self.to_s.encoding; see String#encoding.
#end_with?(*strings) ⇒ Boolean

Equivalent to self.to_s.end_with?; see String#end_with?.
#id2name

Alias for #to_s.
#inspect ⇒ String

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

Alias for #to_sym.
#length ⇒ Integer (also: #size)

Equivalent to self.to_s.length; see String#length.
#match(pattern, offset = 0) ⇒ MatchData^?

Equivalent to self.to_s.match, including possible updates to global variables; see String#match.
#match?(pattern, offset) ⇒ Boolean

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

Returns a frozen string representation of self (not including the leading colon):
#next (also: #succ)

Equivalent to self.to_s.succ.to_sym:
#size ⇒ Integer

Alias for #length.
#[](index) ⇒ String^?

Alias for #[].
#start_with?(*string_or_regexp) ⇒ Boolean

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

Alias for #next.
#swapcase(*options) ⇒ Symbol

Equivalent to sym.to_s.swapcase.to_sym.
#to_proc ⇒ Proc

Returns a ::Proc object which calls the method with name of self on the first parameter and passes the remaining parameters to the method.
#to_s ⇒ String (also: #id2name)

Returns a string representation of self (not including the leading colon):
#to_sym ⇒ self (also: #intern)

Returns self.
#upcase(*options) ⇒ Symbol

Equivalent to sym.to_s.upcase.to_sym.

`::Comparable` - Included

#<	Compares two objects based on the receiver’s #<=> method, returning true if it returns a value less than 0.
#<=	Compares two objects based on the receiver’s #<=> method, returning true if it returns a value less than or equal to 0.
#==	Compares two objects based on the receiver’s #<=> method, returning true if it returns 0.
#>	Compares two objects based on the receiver’s #<=> method, returning true if it returns a value greater than 0.
#>=	Compares two objects based on the receiver’s #<=> method, returning true if it returns a value greater than or equal to 0.
#between?	Returns `false` if obj #<=> min is less than zero or if obj #<=> max is greater than zero, `true` otherwise.
#clamp	In `(min, max)` form, returns min if obj #<=> min is less than zero, max if obj #<=> max is greater than zero, and obj otherwise.

Class Method Details

.all_symbols ⇒ `Symbol`

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

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

[ GitHub ]

# File 'string.c', line 12493


static VALUE
sym_all_symbols(VALUE _)
{
    return rb_sym_all_symbols();
}

Instance Attribute Details

#empty? ⇒ `Boolean` (readonly)

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

[ GitHub ]

# File 'string.c', line 12333


static VALUE
sym_empty(VALUE sym)
{
    return rb_str_empty(rb_sym2str(sym));
}

Instance Method Details

#<=>(object) ⇒ `1`, ...

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#<=>.

[ GitHub ]

# File 'string.c', line 12203


static VALUE
sym_cmp(VALUE sym, VALUE other)
{
    if (!SYMBOL_P(other)) {
        return Qnil;
    }
    return rb_str_cmp_m(rb_sym2str(sym), rb_sym2str(other));
}

#==

[ GitHub ]

#===

[ GitHub ]

#=~(object) ⇒ Integer^?

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

[ GitHub ]

# File 'string.c', line 12256


static VALUE
sym_match(VALUE sym, VALUE other)
{
    return rb_str_match(rb_sym2str(sym), other);
}

#[](index) ⇒ String^? #[](start, length) ⇒ String^? #[](range) ⇒ String^? #[](substring) ⇒ String^?
Also known as: #slice

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

[ GitHub ]

# File 'string.c', line 12306


static VALUE
sym_aref(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_aref_m(argc, argv, rb_sym2str(sym));
}

#capitalize(*options) ⇒ `Symbol`

Equivalent to sym.to_s.capitalize.to_sym.

See String#capitalize.

[ GitHub ]

# File 'string.c', line 12383


static VALUE
sym_capitalize(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_intern(rb_str_capitalize(argc, argv, rb_sym2str(sym)));
}

#casecmp(object) ⇒ `1`, ...

Like #<=>, 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 #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: #casecmp?, String#casecmp.

[ GitHub ]

# File 'string.c', line 12220


static VALUE
sym_casecmp(VALUE sym, VALUE other)
{
    if (!SYMBOL_P(other)) {
        return Qnil;
    }
    return str_casecmp(rb_sym2str(sym), rb_sym2str(other));
}

#casecmp?(object) ⇒ `true`, ...

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 #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: #casecmp, String#casecmp?.

[ GitHub ]

# File 'string.c', line 12237


static VALUE
sym_casecmp_p(VALUE sym, VALUE other)
{
    if (!SYMBOL_P(other)) {
        return Qnil;
    }
    return str_casecmp_p(rb_sym2str(sym), rb_sym2str(other));
}

#downcase(*options) ⇒ `Symbol`

Equivalent to sym.to_s.downcase.to_sym.

See String#downcase.

Related: #upcase.

[ GitHub ]

# File 'string.c', line 12367


static VALUE
sym_downcase(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_intern(rb_str_downcase(argc, argv, rb_sym2str(sym)));
}

#encoding ⇒ Encoding

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

[ GitHub ]

# File 'string.c', line 12442


static VALUE
sym_encoding(VALUE sym)
{
    return rb_obj_encoding(rb_sym2str(sym));
}

#end_with?(*strings) ⇒ `Boolean`

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

[ GitHub ]

# File 'string.c', line 12428


static VALUE
sym_end_with(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_end_with(argc, argv, rb_sym2str(sym));
}

#id2name

Alias for #to_s.

[ GitHub ]

# File 'symbol.rb', line 15


alias id2name to_s

#inspect ⇒ String

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

:foo.inspect # => ":foo"

Related: #to_s, #name.

[ GitHub ]

# File 'string.c', line 12112


static VALUE
sym_inspect(VALUE sym)
{
    VALUE str = rb_sym2str(sym);
    const char *ptr;
    long len;
    char *dest;

    if (!rb_str_symname_p(str)) {
        str = rb_str_inspect(str);
        len = RSTRING_LEN(str);
        rb_str_resize(str, len + 1);
        dest = RSTRING_PTR(str);
        memmove(dest + 1, dest, len);
    }
    else {
        rb_encoding *enc = STR_ENC_GET(str);
        VALUE orig_str = str;

        len = RSTRING_LEN(orig_str);
        str = rb_enc_str_new(0, len + 1, enc);

        // Get data pointer after allocation
        ptr = RSTRING_PTR(orig_str);
        dest = RSTRING_PTR(str);
        memcpy(dest + 1, ptr, len);

        RB_GC_GUARD(orig_str);
    }
    dest[0] = ':';

    RUBY_ASSERT_BUILTIN_TYPE(str, T_STRING);

    return str;
}

#intern

Alias for #to_sym.

[ GitHub ]

# File 'symbol.rb', line 41


alias intern to_sym

#length ⇒ Integer Also known as: #size

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

[ GitHub ]

# File 'string.c', line 12319


static VALUE
sym_length(VALUE sym)
{
    return rb_str_length(rb_sym2str(sym));
}

#match(pattern, offset = 0) ⇒ MatchData^? #match(pattern, offset = 0) {|matchdata| ... } ⇒ Object

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

[ GitHub ]

# File 'string.c', line 12273


static VALUE
sym_match_m(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_match_m(argc, argv, rb_sym2str(sym));
}

#match?(pattern, offset) ⇒ `Boolean`

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

[ GitHub ]

# File 'string.c', line 12288


static VALUE
sym_match_m_p(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_match_m_p(argc, argv, sym);
}

#name ⇒ String

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

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

Related: #to_s, #inspect.

[ GitHub ]

# File 'symbol.rb', line 26


def name
  Primitive.attr! :leaf
  Primitive.cexpr! 'rb_sym2str(self)'
end

#next Also known as: #succ

Equivalent to self.to_s.succ.to_sym:

:foo.succ # => :fop

Related: String#succ.

[ GitHub ]

# File 'string.c', line 12179


static VALUE
sym_succ(VALUE sym)
{
    return rb_str_intern(rb_str_succ(rb_sym2str(sym)));
}

#length ⇒ Integer #size ⇒ Integer

Alias for #length.

#[](index) ⇒ String^? #[](start, length) ⇒ String^? #[](range) ⇒ String^? #[](substring) ⇒ String^?

Alias for #[].

#start_with?(*string_or_regexp) ⇒ `Boolean`

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

[ GitHub ]

# File 'string.c', line 12413


static VALUE
sym_start_with(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_start_with(argc, argv, rb_sym2str(sym));
}

#next #succ

Alias for #next.

#swapcase(*options) ⇒ `Symbol`

Equivalent to sym.to_s.swapcase.to_sym.

See String#swapcase.

[ GitHub ]

# File 'string.c', line 12399


static VALUE
sym_swapcase(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_intern(rb_str_swapcase(argc, argv, rb_sym2str(sym)));
}

#to_proc ⇒ Proc

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"]

[ GitHub ]

# File 'proc.c', line 1477


VALUE
rb_sym_to_proc(VALUE sym)
{
    static VALUE sym_proc_cache = Qfalse;
    enum {SYM_PROC_CACHE_SIZE = 67};
    VALUE proc;
    long index;
    ID id;

    if (!sym_proc_cache) {
        sym_proc_cache = rb_ary_hidden_new(SYM_PROC_CACHE_SIZE * 2);
        rb_vm_register_global_object(sym_proc_cache);
        rb_ary_store(sym_proc_cache, SYM_PROC_CACHE_SIZE*2 - 1, Qnil);
    }

    id = SYM2ID(sym);
    index = (id % SYM_PROC_CACHE_SIZE) << 1;

    if (RARRAY_AREF(sym_proc_cache, index) == sym) {
        return RARRAY_AREF(sym_proc_cache, index + 1);
    }
    else {
        proc = sym_proc_new(rb_cProc, ID2SYM(id));
        RARRAY_ASET(sym_proc_cache, index, sym);
        RARRAY_ASET(sym_proc_cache, index + 1, proc);
        return proc;
    }
}

#to_s ⇒ String Also known as: #id2name

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

:foo.to_s # => "foo"

Related: #inspect, #name.

[ GitHub ]

# File 'symbol.rb', line 10


def to_s
  Primitive.attr! :leaf
  Primitive.cexpr! 'rb_sym_to_s(self)'
end

#to_sym ⇒ `self` Also known as: #intern

Returns self.

Related: String#to_sym.

[ GitHub ]

# File 'symbol.rb', line 37


def to_sym
  self
end

#upcase(*options) ⇒ `Symbol`

Equivalent to sym.to_s.upcase.to_sym.

See String#upcase.

[ GitHub ]

# File 'string.c', line 12349


static VALUE
sym_upcase(int argc, VALUE *argv, VALUE sym)
{
    return rb_str_intern(rb_str_upcase(argc, argv, rb_sym2str(sym)));
}

Class: Symbol

Overview

What’s Here

Methods for Querying

Methods for Comparing

Methods for Converting

Class Method Summary

Instance Attribute Summary

Instance Method Summary

::Comparable - Included

Class Method Details

.all_symbols ⇒ Symbol

Instance Attribute Details

#empty? ⇒ Boolean (readonly)

Instance Method Details

#<=>(object) ⇒ 1, ...

#==

#===

#=~(object) ⇒ Integer?

#[](index) ⇒ String? #[](start, length) ⇒ String? #[](range) ⇒ String? #[](substring) ⇒ String? Also known as: #slice

#capitalize(*options) ⇒ Symbol

#casecmp(object) ⇒ 1, ...

#casecmp?(object) ⇒ true, ...

#downcase(*options) ⇒ Symbol

#encoding ⇒ Encoding

#end_with?(*strings) ⇒ Boolean

#id2name

#inspect ⇒ String

#intern

#length ⇒ Integer Also known as: #size

#match(pattern, offset = 0) ⇒ MatchData? #match(pattern, offset = 0) {|matchdata| ... } ⇒ Object

#match?(pattern, offset) ⇒ Boolean

#name ⇒ String

#next Also known as: #succ

#length ⇒ Integer #size ⇒ Integer

#[](index) ⇒ String? #[](start, length) ⇒ String? #[](range) ⇒ String? #[](substring) ⇒ String?

#start_with?(*string_or_regexp) ⇒ Boolean

#next #succ

#swapcase(*options) ⇒ Symbol

#to_proc ⇒ Proc

#to_s ⇒ String Also known as: #id2name

#to_sym ⇒ self Also known as: #intern

#upcase(*options) ⇒ Symbol

`::Comparable` - Included

.all_symbols ⇒ `Symbol`

#empty? ⇒ `Boolean` (readonly)

#<=>(object) ⇒ `1`, ...

#=~(object) ⇒ Integer^?

#[](index) ⇒ String^? #[](start, length) ⇒ String^? #[](range) ⇒ String^? #[](substring) ⇒ String^?
Also known as: #slice

#capitalize(*options) ⇒ `Symbol`

#casecmp(object) ⇒ `1`, ...

#casecmp?(object) ⇒ `true`, ...

#downcase(*options) ⇒ `Symbol`

#end_with?(*strings) ⇒ `Boolean`

#match(pattern, offset = 0) ⇒ MatchData^? #match(pattern, offset = 0) {|matchdata| ... } ⇒ Object

#match?(pattern, offset) ⇒ `Boolean`

#[](index) ⇒ String^? #[](start, length) ⇒ String^? #[](range) ⇒ String^? #[](substring) ⇒ String^?

#start_with?(*string_or_regexp) ⇒ `Boolean`

#swapcase(*options) ⇒ `Symbol`

#to_sym ⇒ `self` Also known as: #intern

#upcase(*options) ⇒ `Symbol`