From: dblack@...
Date: 2002-11-26T12:56:34+09:00
Subject: Re: Things That Newcomers to Ruby Should Know (11/24/02)

Hi --

On Tue, 26 Nov 2002, Daniel Carrera wrote:

> [snip]
> > 4 is an unmodifiable object.  "Hello".chomp! is fine because "Hello" is a
> > modifiable object.
>
> Thanks, I'm understanding more now.  I guess that the next logical
> question is why is 4 unmodifiable and "a" modifiable?  I don't see why a
> string would be modifiable and a number not.
>
> Just like you can say that the number 4 is set, and cannot be turned into
> a 5, you can also say that the letter "a" is set and cannot be turned into
> a "b".  Yet, I can write:
>
> "a".gsub!(/a/,"b")

You're not changing the letter 'a' itself; you're changing a string
which has the letter 'a' in it.

To put it another way:

You can have more than one "a" string:

  s = "a"
  t = "a"

and if you change or increment s:

  s.succ!   # s is now "b"

t doesn't change.

But there's only one of each number.  If you were allowed to do

  3.succ!

or

  3 += 1

then when you did this:

  puts 3 * 5

the output would be "20", because you would have incremented the
actual object 3.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav