From: dblack@...
Date: 2006-01-05T08:13:13+09:00
Subject: Re: On Symbols

Hi --

On Thu, 5 Jan 2006, Dave Howell wrote:

> dblack said:
>> a = "string" # a contains a reference to that string
>>  a = 1        # a contains the actual (immediate) value 1
>
> Except the example would seem to contradict this statement. `a' `b' and `c' 
> do not contain actual anythings. They contain references to the same object, 
> that object which is the value "1".
>
> Maybe. I guess it depends on what, exactly, the .object_id method returns, or 
> on what "actual" or "immediate" means. It would appear it means something 
> much less immediate than I'd expect.

I've always conceptualized it as pretty much a value vs. pointer
difference.  I avoid the word "pointer" because (a) Matz never calls
it that, and (b) it's not a matter of physical memory, but a Ruby-side
notion of reference.  Still, it's close to the same idea.

Fixnums, Symbols, true, false, and nil get assigned directly to
variables.  For other objects, variables get a reference to the
object.  References, like variables, are not themselves objects.
They're part of a kind of language substratum on which the object
system floats.

I think that's all there is to it.  In fact, in a sense there's even
less to it, since Ruby handles any necessary de-referencing for you,
so you don't have to make any explicit distinction in your code.

> Once again, a gentle reminder: please feel free to comment on the learning 
> process I'm documenting if you like, but do NOT respond if you're going to 
> try to explain more about symbols and whatnot. Thanks!

I'm giving myself a directly-quoted-person exemption :-)


David

-- 
David A. Black
dblack@wobblini.net

"Ruby for Rails", from Manning Publications, coming April 2006!
http://www.manning.com/books/black