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Showing content from https://docs.ruby-lang.org/en/master/Digest/../Symbol.html below:

class Symbol - Documentation for Ruby 3.5

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   
$f2.object_id   
$f3.object_id   

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

One.instance_methods(true)

One.instance_variables

One.class_variables

global_variables.grep(/six/)

local_variables

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

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

• ::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.

• <=>: 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.

• 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.

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

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

Symbol.all_symbols.size    
Symbol.all_symbols.take(3) 

def self.json_create(o)
  o['s'].to_sym
end

See as_json.

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));
}

If object is a symbol, returns the equivalent of symbol.to_s <=> object.to_s:

:bar <=> :foo 
:foo <=> :foo 
:foo <=> :bar 

Otherwise, returns nil:

:foo <=> 'bar' 

Related: String#<=>.

#define sym_equal rb_obj_equal

Returns true if object is the same object as self, false otherwise.

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

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

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

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

def as_json(*)
  {
    JSON.create_id => self.class.name,
    's'            => to_s,
  }
end

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

Method JSON.create deserializes such a hash, returning a Symbol object:

Symbol.json_create(x) 

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

Equivalent to sym.to_s.capitalize.to_sym.

See String#capitalize.

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

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

lower = :abc
upper = :ABC
upper.casecmp(lower) 
lower.casecmp(lower) 
lower.casecmp(upper) 

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) 
:foo.casecmp(2)        

Unlike Symbol#casecmp?, case-insensitivity does not work for characters outside of ‘A’..‘Z’ and ‘a’..‘z’:

lower = :äöü
upper = :ÄÖÜ
upper.casecmp(lower) 
lower.casecmp(lower) 
lower.casecmp(upper) 

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));
}

Returns true if self and object are equal after Unicode case folding, otherwise false:

lower = :abc
upper = :ABC
upper.casecmp?(lower) 
lower.casecmp?(lower) 
lower.casecmp?(upper) 

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) 
:foo.casecmp?(2)        

Unlike Symbol#casecmp, works for characters outside of ‘A’..‘Z’ and ‘a’..‘z’:

lower = :äöü
upper = :ÄÖÜ
upper.casecmp?(lower) 
lower.casecmp?(lower) 
lower.casecmp?(upper) 

Related: Symbol#casecmp, String#casecmp?.

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

Equivalent to sym.to_s.downcase.to_sym.

See String#downcase.

Related: Symbol#upcase.

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

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

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

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

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

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

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;
}

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

:foo.inspect 

Related: Symbol#to_s, Symbol#name.

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

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

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

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

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

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

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

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

:foo.name         
:foo.name.frozen? 

Related: Symbol#to_s, Symbol#inspect.

Equivalent to self.to_s.succ.to_sym:

:foo.succ 

Related: String#succ.

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.start_with?; see String#start_with?.

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

Equivalent to self.to_s.succ.to_sym:

:foo.succ 

Related: String#succ.

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

Equivalent to sym.to_s.swapcase.to_sym.

See String#swapcase.

def to_json(state = nil, *a)
  state = ::JSON::State.from_state(state)
  if state.strict?
    super
  else
    as_json.to_json(state, *a)
  end
end

Returns a JSON string representing self:

require 'json/add/symbol'
puts :foo.to_json

Output:

Calls superclass method

VALUE
rb_sym_to_proc(VALUE sym)
{
    enum {SYM_PROC_CACHE_SIZE = 67};

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

        ID id = SYM2ID(sym);
        long index = (id % SYM_PROC_CACHE_SIZE);
        VALUE procval = RARRAY_AREF(sym_proc_cache, index);
        if (RTEST(procval)) {
            rb_proc_t *proc;
            GetProcPtr(procval, proc);

            if (proc->block.as.symbol == sym) {
                return procval;
            }
        }

        procval = sym_proc_new(rb_cProc, sym);
        RARRAY_ASET(sym_proc_cache, index, procval);

        return RB_GC_GUARD(procval);
    }
    else {
        return sym_proc_new(rb_cProc, 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.call(1000)        
proc.call(1000, 16)    
(1..3).collect(&:to_s) 

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

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

:foo.to_s 

Related: Symbol#inspect, Symbol#name.

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

Equivalent to sym.to_s.upcase.to_sym.

See String#upcase.

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