From: Brian Candler <B.Candler@...>
Date: 2007-05-19T21:56:07+09:00
Subject: Re: Why was the "Symbol is a String"-idea dropped?

On Sat, May 19, 2007 at 08:28:24AM +0900, Rick DeNatale wrote:
> Most normal objects are referenced at the C level by an internal value
> which is a pointer to the objects state representation in memory.
> Since objects are aligned at least on a word boudary, all normal
> object pointers will have the 2 least significant bits as zero. They
> will also be non-zero
> 
> A few objects are immediate which means that they are referenced at
> the C level by a representation whose value is not a pointer.  Fixnums
> are represented by shifting the C representation left one bit and
> turning on the low-order bit.  False is represented by 0, True by 2,
> and Nil by 4.
> 
> Ruby symbols are represented by a value computed by shifting the
> symbols integer representation left 8 bits and setting the low-order
> byte to 0xFF representation

Perhaps it varies based on the Ruby version you're running; it's not like
that for me.

irb(main):006:0> :foo.object_id.to_s(16)
=> "39490e"
irb(main):007:0> RUBY_VERSION
=> "1.8.4"

I think a weaker requirement than 'immediate' is needed. A symbol can quite
happily be a regular object; we just need to ensure that there is always
only one symbol for a particular symbol character sequence.

Regards,

Brian.