From: Austin Ziegler <austin@...>
Date: 2002-11-26T13:29:05+09:00
Subject: Re: Things That Newcomers to Ruby Should Know (11/24/02)

On Tue, 26 Nov 2002 12:28:15 +0900, Gavin Sinclair wrote:
>>> It's applicable to a small subset of the total set of classes.
>>> Really, x++ is the same as x.succ!, and x.succ! won't work
>>> because there's no assignment and you can't change self.
>> I don't follow that. Why is it that I can do string.chomp! but it
>> is not conceivable to do x.succ!? Aren't you changing self with
>> string.chomp!?
> No. Hopefully the following makes sense.

More to the point:

irb(main):004:0> s = "Hello"
"Hello"
irb(main):005:0> s.id
20841200
irb(main):006:0> s.succ!
"Hellp"
irb(main):007:0> s.id
20841200
irb(main):008:0> 

> The prevailing point is that "x = 4; x++" translates into Ruby
> most closely as
>   x = 4
>   x.succ!
> 
> Of course, Integer#succ! is not defined, for good reason. What
> does 4.succ! mean? Turn all 4's into 5's?
> 
> 4 is an unmodifiable object. "Hello".chomp! is fine because
> "Hello" is a modifiable object.

Actually, I think that the proper term is that 4 is an immediate
object. It's the immediacy (and the "singleton-object" nature of
Fixnums) which makes the difference.

This leads, of course, to an interesting question. How can one
implement a Fixnum-like behaviour ("singleton-object") in any given
Ruby class? (That is, one and only one instance of a given value.)

-austin
-- Austin Ziegler, austin@halostatue.ca on 2002.11.25 at 23.26.11