From: Pascal Hurni <pascal_hurni@...>
Date: 2006-05-18T22:56:24+09:00
Subject: Re: instance variables for Fixnum?

Daniel Schierbeck wrote:
> 
> Almost everything in Ruby is an object -- even Fixnums. There is only 
> one `3' object -- it's not like a string, where two strings with the 
> same content can very well be different objects.
> 
>    "foo".instance_variable_set(:@bar, "baz")
>    "foo".instance_variable_get(:@bar)  => ArgumentError

Yes, that's ok

> 
>    3.instance_variable_set(:@bar, "baz")
>    3.instance_variable_get(:@bar)  => "baz"
> 
> This is because Fixnums are immediates; so are symbols, btw.
> 

Well, I found in the ruby sources, why this is possible.

Every 'normal' object has a hashtable for instance variables, this is the
normal behaviour as we expect. But immediates don't have a hashtable,
because they are encoded as values (bits) directly in the VALUE type.

To mimic the 'object' behaviour, Matz created a 'generic_iv_tbl' which
holds the instance variables of immediates for which a 'instance_variable_set'
has been made. This is the magic.