From: Brian Candler <B.Candler@...>
Date: 2007-03-08T16:02:02+09:00
Subject: Re: Paul Graham explains Ruby symbols

On Thu, Mar 08, 2007 at 02:46:43PM +0900, Chad Perrin wrote:
> On Thu, Mar 08, 2007 at 04:21:10AM +0900, Bharat Ruparel wrote:
> > I think of symbols is immutable strings that are useful only in 
> > referring to some values?  Seems like a nice way for using pointers 
> > without all the warps?
> 
> "Immutable strings" doesn't work so well, since a string literal is
> "immutable" anyway.

Well maybe that's technically right, in the sense that the source code
itself is immutable. However, every time a string literal is 'executed' a
new, mutable string object is instantiated:

5.times { puts "hello".object_id }

So there's no way in practice to make use of the 'immutable' property you
describe, because every String object your program sees is mutable.

5.times {
  a = "hello"
  a << "!"     # changed it
}

Here's where I'd say a symbol is different:

5.times {
  a = :hello
  puts a.object_id   # same every time round
  a << "!"           # fails (symbol has no mutating methods)
}

Regards,

Brian.