class Symbol
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:
-
Inherits from class Object.
-
Includes module Comparable.
Here, class Symbol provides methods that are useful for:
Methods for Querying¶ ↑
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::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 givenRegexpor other object; returnsnilif no match is found. -
[],slice: Returns a substring of symbol determined by a given index, start/length, or range, or string. -
empty?: Returnstrueifself.lengthis zero;falseotherwise. -
encoding: Returns theEncodingobject that represents the encoding of symbol. -
end_with?: Returnstrueif symbol ends with any of the given strings. -
match: Returns aMatchDataobject if symbol matches a givenRegexp;nilotherwise. -
match?: Returnstrueif symbol matches a givenRegexp;falseotherwise. -
start_with?: Returnstrueif symbol starts with any of the given strings.
Methods for Comparing¶ ↑
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<=>: Returns -1, 0, or 1 as a given symbol is smaller than, equal to, or larger than symbol. -
==,===: Returnstrueif 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?: Returnstrueif symbol is equal to a given symbol after Unicode case folding;falseotherwise.
Methods for Converting¶ ↑
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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 ofselfas 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 aProcobject which responds to the method named by symbol. -
upcase: Returns symbol with all characters upcased.
Public Class Methods
Returns an array of all symbols currently in Ruby’s symbol table:
Symbol.all_symbols.size # => 9334 Symbol.all_symbols.take(3) # => [:!, :"\"", :"#"]
static VALUE
sym_all_symbols(VALUE _)
{
return rb_sym_all_symbols();
}
See as_json.
# File ext/json/lib/json/add/symbol.rb, line 45 def self.json_create(o) o['s'].to_sym end
Public 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#<=>.
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));
}
Returns true if object is the same object as self, false otherwise.
#define sym_equal rb_obj_equal
Equivalent to symbol.to_s =~ object, including possible updates to global variables; see String#=~.
static VALUE
sym_match(VALUE sym, VALUE other)
{
return rb_str_match(rb_sym2str(sym), other);
}
Equivalent to symbol.to_s[]; see String#[].
static VALUE
sym_aref(int argc, VALUE *argv, VALUE sym)
{
return rb_str_aref_m(argc, argv, rb_sym2str(sym));
}
Methods Symbol#as_json and Symbol.json_create may be used to serialize and deserialize a Symbol object; see Marshal.
Method Symbol#as_json serializes self, returning a 2-element hash representing self:
require 'json/add/symbol' x = :foo.as_json # => {"json_class"=>"Symbol", "s"=>"foo"}
Method JSON.create deserializes such a hash, returning a Symbol object:
Symbol.json_create(x) # => :foo
# File ext/json/lib/json/add/symbol.rb, line 24 def as_json(*) { JSON.create_id => self.class.name, 's' => to_s, } end
Equivalent to sym.to_s.capitalize.to_sym.
See String#capitalize.
static VALUE
sym_capitalize(int argc, VALUE *argv, VALUE sym)
{
return rb_str_intern(rb_str_capitalize(argc, argv, rb_sym2str(sym)));
}
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.
static VALUE
sym_casecmp(VALUE sym, VALUE other)
{
if (!SYMBOL_P(other)) {
return Qnil;
}
return str_casecmp(rb_sym2str(sym), rb_sym2str(other));
}
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?.
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));
}
Equivalent to sym.to_s.downcase.to_sym.
See String#downcase.
Related: Symbol#upcase.
static VALUE
sym_downcase(int argc, VALUE *argv, VALUE sym)
{
return rb_str_intern(rb_str_downcase(argc, argv, rb_sym2str(sym)));
}
Returns true if self is :'', false otherwise.
static VALUE
sym_empty(VALUE sym)
{
return rb_str_empty(rb_sym2str(sym));
}
Equivalent to self.to_s.encoding; see String#encoding.
static VALUE
sym_encoding(VALUE sym)
{
return rb_obj_encoding(rb_sym2str(sym));
}
Equivalent to self.to_s.end_with?; see String#end_with?.
static VALUE
sym_end_with(int argc, VALUE *argv, VALUE sym)
{
return rb_str_end_with(argc, argv, rb_sym2str(sym));
}
Returns a string representation of self (including the leading colon):
:foo.inspect # => ":foo"
Related: Symbol#to_s, Symbol#name.
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;
RSTRING_GETMEM(orig_str, ptr, len);
str = rb_enc_str_new(0, len + 1, enc);
dest = RSTRING_PTR(str);
memcpy(dest + 1, ptr, len);
RB_GC_GUARD(orig_str);
}
dest[0] = ':';
return str;
}
Equivalent to self.to_s.length; see String#length.
static VALUE
sym_length(VALUE sym)
{
return rb_str_length(rb_sym2str(sym));
}
Equivalent to self.to_s.match, including possible updates to global variables; see String#match.
static VALUE
sym_match_m(int argc, VALUE *argv, VALUE sym)
{
return rb_str_match_m(argc, argv, rb_sym2str(sym));
}
Equivalent to sym.to_s.match?; see String#match.
static VALUE
sym_match_m_p(int argc, VALUE *argv, VALUE sym)
{
return rb_str_match_m_p(argc, argv, sym);
}
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.
VALUE
rb_sym2str(VALUE sym)
{
if (DYNAMIC_SYM_P(sym)) {
return RSYMBOL(sym)->fstr;
}
else {
return rb_id2str(STATIC_SYM2ID(sym));
}
}
Equivalent to self.to_s.start_with?; see String#start_with?.
static VALUE
sym_start_with(int argc, VALUE *argv, VALUE sym)
{
return rb_str_start_with(argc, argv, rb_sym2str(sym));
}
Equivalent to self.to_s.succ.to_sym:
:foo.succ # => :fop
Related: String#succ.
static VALUE
sym_succ(VALUE sym)
{
return rb_str_intern(rb_str_succ(rb_sym2str(sym)));
}
Equivalent to sym.to_s.swapcase.to_sym.
See String#swapcase.
static VALUE
sym_swapcase(int argc, VALUE *argv, VALUE sym)
{
return rb_str_intern(rb_str_swapcase(argc, argv, rb_sym2str(sym)));
}
Returns a JSON string representing self:
require 'json/add/symbol' puts :foo.to_json
Output:
# {"json_class":"Symbol","s":"foo"}
# File ext/json/lib/json/add/symbol.rb, line 40 def to_json(*a) as_json.to_json(*a) end
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"]
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_gc_register_mark_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;
}
}
Returns a string representation of self (not including the leading colon):
:foo.to_s # => "foo"
Related: Symbol#inspect, Symbol#name.
VALUE
rb_sym_to_s(VALUE sym)
{
return str_new_shared(rb_cString, rb_sym2str(sym));
}
Equivalent to sym.to_s.upcase.to_sym.
See String#upcase.
static VALUE
sym_upcase(int argc, VALUE *argv, VALUE sym)
{
return rb_str_intern(rb_str_upcase(argc, argv, rb_sym2str(sym)));
}