From: "David A. Black" <dblack@...>
Date: 2008-07-14T20:43:30+09:00
Subject: Re: Help with class instance variables

Hi --

On Mon, 14 Jul 2008, Ittay Dror wrote:

> Hi,
>
> David A. Black wrote:
>> Hi --
>>
>>
>> The problem is that the instance variables you're initializing belong
>> to the singleton class of Platform (class << Platform), not Platform.
>> Compare with this:
>>
>>    class C
>>      class << self
>>        attr_accessor :x
>>      end
>>
>>      @x = 1    # or self.x = 1
>>    end
>>
>>    puts C.x    # 1
>>
>
> Ok, thank you, that cleared things. I have two follow up questions:
> 1. If I want to add an instance variable to an object of class C I can
> only do that in a method (not as part of the class definition)? In the
> example above, how can I change it so that C.new will return an instance
> of C where '@x' of the instance is 1?

class C
   def initialize
     @x = 1
   end
end

> 2. Is there an analogous way to 'initialize' to write initialization of
> class variables?

Change @x to @@x. Keep in mind, though, that in spite of the similar
appearance, class variables are completely different from instance
variables in just about every possible respect.


David

-- 
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