From: Christoph <chr_mail@...>
Date: 2003-12-03T01:07:15+09:00
Subject: Re: Attempted roadmap of future instance variables....

David A. Black wrote:
...
> Hi --
> 
> I figure that I owe the world at least a shot at clearing the 
> cobwebs (of my own creation, that is :-) on this instance 
> variable thing.  
> 
> So... for those still reading... here's what I *really* think is being
> proposed:

I do ...

> 
> 
> class A
>   def m
>     @var  = "hi"          # regular instance variable
>     @_var = "hello"       # class-local instance variable
>   end
> end
> 
> class B < A
>   def n
>     puts @var             # same as @var, above
>     puts @_var            # not same as @_var above
>   end
> end                       
> 
> o = B.new
> o.m
> o.n
> 
> => Output:
> 
>    hi      # the @var that was set in A#m is used here
>    nil     # the @_var that was in A#m is *not* used here
>            # (because we're now in a method defined in B,
>            # a subclass of A, and class local instance
>            # variables are not shared by subclasses)
> 
> In other words: 
> 
>   * Regular instance variables live per-name per-object
>     (o has exactly one @var).  
> 
>   * Class-local instance variables live per-name per-object per-class
>     (o's methods defined in A have a @_var, and o's methods defined in
>     B have a different @_var).

Thank you very for this comprehensive write up ...


/Christoph