From: Martin DeMello <martindemello@...>
Date: 2005-07-26T14:15:59+09:00
Subject: Re: Trying to understand symbols

Jay Levitt <jay+news@jay.fm> wrote:
> In article <Pine.LNX.4.61.0507251714050.14123@wobblini>, 
> dblack@wobblini.net says...
> > The :foo in send(:foo) is just a symbol (instance of Symbol :-).  It
> > has no special status beyond that.  It happens to match the name of a
> > method, but the symbol object has no relation to that method.
> 
> Really?  Is that always true - a Ruby symbol is essentially a C enum 
> except that you can't define an int value for it?

Sort of, though they're closer to lisp atoms - immutable strings stored
in a special lookup table. They are convertible to/from strings using
String#to_sym and Symbol#to_s. They do respond to object equality, if
that's what you meant - 
a = 'hello'; 
b = 'hello'; 
c = a.to_sym;
d = b.to_sym
p [a, b, c, d].map {|i| i.object_id} #=> c and d are the same object

> So that would mean that Rails's use of symbols (e.g. attr_reader :foo) 
> is just a convention, and Rails uses the symbol-name to go look up an 
> Object with the same name, thus appearing to releate the Symbol to the 
> Object?

It's a common ruby convention, but yes, attr_reader etc. are just
methods that take Symbol arguments, and could have been written to take
String args instead.

martin