From: dblack@...
Date: 2006-08-07T05:48:56+09:00
Subject: Re: Method behaviour

Hi --

On Mon, 7 Aug 2006, Sard Aukary wrote:

> Some methods like
>
> def change(word)
> 	word[0]='e'
> end
> a="affluent"
> puts a
> change(a)
> puts a
>
> alter the original object outside of the method, where as others don't.
>
> def change(word)
> 	word="fish"
> end
> a="cow"
> puts a
> change(a)
> puts a
>
>
> Why the change in behaviour, what determines it?  Is the only way I can
> write methods that change the original object by using the Ruby methods
> that do this?

It's because there's a distinction between (a) sending a message to an
object, and (b) assigning to a variable.

   a = "cow"     # assignment
   a[0] = 'w'    # send message "[]" to a
   a = "fish"    # assignment -- reusing the identifier 'a'

Whenever you assign to a variable, you're wiping the slate clean: the
variable loses all association with the object it referred to
previously (if any).

The "word[0] = 'e'" expression looks like assignment, but technically
it's calling the method "[]=" on the object word, with the single
argument 'e'.  It's not the same as just plain assignment to an
identifier.


David

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