From: "David A. Black" <dblack@...>
Date: 2009-12-20T04:16:56+09:00
Subject: Re: special cased?

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Hi --

On Sat, 19 Dec 2009, I単aki Baz Castillo wrote:

> El S叩bado, 19 de Diciembre de 2009, Roger Pack escribi坦:
>> This confused me a bit
>>
>> class A
>>  @a = 2
>>  @@a = 3
>>  def self.a
>>    puts [@a, @@a]
>>  end
>> end
>>
>> class B < A; end
>>
>> A.a # [2, 3]
>> B.a # [nil, 3]
>>
>> shouldn't @a just lookup @@a in the parent?  Different treatment for
>> different types of variables?
>
> When you write:
>
>  class A
>    @a = 2
>
> take into account that @a=2 is just parsed when loading class A for first
> time.
> When you later do "class B < A; end", the Ruby interpreter doesn't read the
> line "@a = 2" again as it already parsed class A and just stored in memory the
> methods of class A.

Also, instance variables are always pegged to "self".

   class A
     puts self    # A
     @x = 1
   end

   class B < A
     puts self    # B
     puts @x      # nil
   end

Every object, including every Class object, has its own supply of
instance variable "slots", and the meaning of @var is always
self.instance_variable_get("@var").


David

-- 
David A. Black
Senior Developer, Cyrus Innovation Inc.
THE COMPLEAT RUBYIST, Ruby training with Black/Brown/McAnally!
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