From: "Iñaki Baz Castillo" <ibc@...>
Date: 2009-03-31T08:27:57+09:00
Subject: Re: When to use instance variables @

El Martes 31 Marzo 2009, Joshua Collins escribió:
> All variables in Ruby (Local, Global, Instance (object), or Class) do not
> need to be defined at the beginning of a method.

I didn't say "at the beginning of a method", but "at the beginning of a class" 
(anyhow I was also wrong XD).




> In Ruby, do you need to set that variable before calling it? Yes.

Well, this is different for class variables and instance variables:

--------------
irb> @non_existing_instance_variable
nil

irb> @@non_existing_class_variable
NameError: uninitialized class variable @@non_existing_class_variable in 
Object
        from (irb):2
        from /usr/bin/irb:12:in `<main>'
--------------

What I mean is that class variables MUST be defined (not declared, of course) 
before *reading* them, while an instance variable returns nil if it's not set 
yet.



>           #No need to define the variable before it's value is set
>           @@number_of_squares = 1

Yes, please note that I said:
----------
This is not true when using class variables (@@). These need to be "declared" 
at the beginning of the class
----------
(note the "declared" between ""  XD)


Regards.


-- 
Iñaki Baz Castillo <ibc@aliax.net>