From: "David A. Black" <dblack@...>
Date: 2005-07-24T20:45:19+09:00
Subject: Re: Local Instance Methods

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Hi --

On Sun, 24 Jul 2005, Lionel Thiry wrote:

> Trans a =E9crit :
>> Hi All--
>>
>> I know there are plans to give Ruby private instance variables,
>
> Ruby will have private instance variables? What a good idea! But how
> will that work?

Based on what Matz has said in the past, there will be a @_ variable
prefix.  It's not clear whether @_var will be private, or @var will be
private.  Matz has said he wants to use @_var for whichever is used
less often :-)  (Editorial: I actually think that the ugliness of
@_var is enough to make the whole thing questionable, whichever one
it's used for.  I'd rather see class variables eliminated, and @@var
used for private instance variables.  Then the net amount of
punctuation would stay the same :-)

Anyway... let's say @_var is private.  That means that @_x in a
superclass is different from @_x in a subclass:

   class C
     def set_state(x)
       @_x =3D x
     end
     def show_state
       puts @_
     end
   end

   class D < C
     def set_hundred
       @_x =3D 100
     end
     def show_hundred
       puts @_x
     end
   end

Now if you do:

   d =3D D.new
   d.set_state(1)
   d.set_hundred
   d.show_state    # 1
   d.show_hundred  # 100

In other words, when you use @_x in class D, you're not using the same
instance variables as @_x in class C.  Both "show" methods use @_x,
but they're not the same @_x.


David

--=20
David A. Black
dblack@wobblini.net
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