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¶ ↑
-
::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; returnsnil
if no match is found. -
[]
,slice
: Returns a substring of symbol determined by a given index, start/length, or range, or string. -
empty?
: Returnstrue
ifself.length
is zero;false
otherwise. -
encoding
: Returns theEncoding
object that represents the encoding of symbol. -
end_with?
: Returnstrue
if symbol ends with any of the given strings. -
match
: Returns aMatchData
object if symbol matches a givenRegexp
;nil
otherwise. -
match?
: Returnstrue
if symbol matches a givenRegexp
;false
otherwise. -
start_with?
: Returnstrue
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.
-
==
,===
: Returnstrue
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?
: Returnstrue
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 ofself
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 aProc
object 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(); }
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)); }
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
(not including the leading colon):
:foo.to_s # => "foo"
Related: Symbol#inspect
, Symbol#name
.
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 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))); }