class Symbol - RDoc Documentation

# class Symbol

`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:

- 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.

### Public Class Methods

all_symbols → array click to toggle source

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, :$=, :ThreadGroup,
                                    :wait2, :$>]

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

json_create(o) click to toggle source

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

    # File ext/json/lib/json/add/symbol.rb, line 22
    def self.json_create(o)
      o['s'].to_sym
    end

### Public Instance Methods

symbol <=> other_symbol → -1, 0, +1, or nil click to toggle source

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.

    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));
    }

sym == obj → true or false click to toggle source

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

    #define sym_equal rb_obj_equal

Also aliased as: ===
===(p1)

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

Alias for: ==
sym =~ obj → integer or nil click to toggle source

Returns `sym.to_s =~ obj`.

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

sym[idx] → char click to toggle source
sym[b, n] → string

Returns `sym.to_s[]`.

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

Also aliased as: slice
as_json(*) click to toggle source

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

    # File ext/json/lib/json/add/symbol.rb, line 9
    def as_json(*)
      {
        JSON.create_id => self.class.name,
        's'            => to_s,
      }
    end

capitalize(*options) → symbol click to toggle source

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)));
    }

casecmp(other_symbol) → -1, 0, 1, or nil click to toggle source

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?`.

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

casecmp?(other_symbol) → true, false, or nil click to toggle source

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`.

    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 click to toggle source

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)));
    }

empty? → true or false click to toggle source

Returns whether sym is :“” or not.

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

encoding → encoding click to toggle source

Returns the `Encoding` object that represents the encoding of sym.

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

end_with?([suffixes]+) → true or false click to toggle source

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

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

id2name → string

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`.

Alias for: to_s
inspect → string click to toggle source

Returns the representation of sym as a symbol literal.

    :fred.inspect   #=> ":fred"

    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);
            RSTRING_GETMEM(str, ptr, len);
            str = rb_enc_str_new(0, len + 1, enc);
            dest = RSTRING_PTR(str);
            memcpy(dest + 1, ptr, len);
        }
        dest[0] = ':';
        return str;
    }

intern → sym click to toggle source

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

    static VALUE
    sym_to_sym(VALUE sym)
    {
        return sym;
    }

Also aliased as: to_sym
length → integer click to toggle source

Same as `sym.to_s.length`.

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

Also aliased as: size
match(pattern) → matchdata or nil click to toggle source
match(pattern, pos) → matchdata or nil

Returns `sym.to_s.match`.

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

match?(pattern) → true or false click to toggle source
match?(pattern, pos) → true or false

Returns `sym.to_s.match?`.

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

name → string click to toggle source

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

    VALUE
    rb_sym2str(VALUE sym)
    {

    }

next()

Same as `sym.to_s.succ.intern`.

Alias for: succ
size → integer

Same as `sym.to_s.length`.

Alias for: length
slice(idx) → char
slice(b, n) → string

Returns `sym.to_s[]`.

Alias for: []
start_with?([prefixes]+) → true or false click to toggle source

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

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

succ click to toggle source

Same as `sym.to_s.succ.intern`.

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

Also aliased as: next
swapcase(*options) → symbol click to toggle source

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)));
    }

to_json(*a) click to toggle source

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

    # File ext/json/lib/json/add/symbol.rb, line 17
    def to_json(*a)
      as_json.to_json(*a)
    end

to_proc click to toggle source

Returns a Proc object which responds to the given method by sym.

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

    VALUE
    rb_sym_to_proc(VALUE sym)
    {
    }

to_s → string click to toggle source

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`.

    VALUE
    rb_sym_to_s(VALUE sym)
    {
        return str_new_shared(rb_cString, rb_sym2str(sym));
    }

Also aliased as: id2name
to_sym → sym

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

Alias for: intern
upcase(*options) → symbol click to toggle source

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)));
    }