From: David Garamond <lists@...6.isreserved.com>
Date: 2004-02-26T22:07:06+09:00
Subject: Re: Why don't $global and @instance variables need *initialization*?

Robert Klemme wrote:
>>Sorry if the answer is obvious, but I can't find a satisfactory or more
>>verbose explanation about this. The only thing I found is from the
>>Ruby's User Guide:
>>
>>"As with globals, instance variables have the nil value until they are
>>initialized. Instance variables of ruby do not need declaration. This
>>implies a flexible structure of objects. In fact, each instance variable
>>is dynamically appended to an object when it is first referenced."
>>
>>Could someone explain the above? How is it more flexible?
> 
> You don't need the declaration.  That saves typing and also you can add
> them at runtime as you like:

Oops, my bad English strikes again. The question should have been: "why 
don't $global and @instance need *initialization* (i.e. they are already 
preset to nil)?" In other words, why does it behave like this?


irb(main):001:0> a
NameError: undefined local variable or method `a' for main:Object
         from (irb):1
irb(main):002:0> a=nil; a
=> nil
irb(main):003:0> $a
=> nil
irb(main):004:0> @a
=> nil


... and not like this?


irb(main):001:0> a
NameError: undefined local variable or method `a' for main:Object
         from (irb):1
irb(main):002:0> a=nil; a
=> nil
irb(main):003:0> $a
NameError: undefined global variable `$a'
         from (irb):3
irb(main):004:0> $a=nil; $a
=> nil
irb(main):005:0> @a
NameError: undefined instance variable `@a'
         from (irb):5
irb(main):006:0> @a=nil; @a
=> nil

-- 
dave