From: Timothy Hunter <cyclists@...>
Date: 2005-06-05T05:20:25+09:00
Subject: Re: Question about string's in-place modification

Sam Kong wrote:
> Hello!
> 
> I wonder how destructive methods work in the behind.
> 
> For example,
> 
> s = '12345'
> s2 = s
> s.sub!('3', 'three')
> puts s #->'12three45'
> puts s2 #->'12three45'
> 
> Destructive methods are in-place.
> Does that mean the object doesn't change its location in memory?
> Probably not.
> I don't think it's possible as the object might need more space and
> need to move to a bigger empty space for the changed data.
> If it moves, the references pointing to it should be updated as well.
> 
> How exactly does that work?
> 
> Thanks in advance.
> Sam
> 

Don't think of an object's id as a memory address. Think of it as a 
handle for a memory address. That way, if the memory address of an 
object needs to change (if, for example, Ruby needs to allocate more 
memory for a string) Ruby can update the id with the new address and the 
id can remain the same.