From: James Edward Gray II <james@...>
Date: 2005-07-03T00:40:05+09:00
Subject: Re: class variable leading a double life

On Jul 2, 2005, at 9:55 AM, Amarison wrote:

> Can someone please explain why the @var variable leads a double  
> life? One
> for instances and one for the class itself?

@var refers to an instance variable of the current "self" object.

> class Test
>  def Test.inc
>   @var ||= 0
>   @var += 1
>  end

Here self is Test.

>  def inc
>   @var ||= 0
>   @var += 1
>  end
> end

And here, self is an instance of Test.  Two different objects, two  
different variables.

>
> puts Test.inc
>
> x = Test.new
> puts x.inc
>
> y = Test.new
> puts y.inc
>
> #-------------
>
> puts Test.inc
> puts x.inc
> puts y.inc

If you want it to be the same variable in both places, you need a  
class variable:

class Test
@@var = 0

def Test.inc
   @@var += 1
end

def inc
   @@var += 1
end
end


puts Test.inc

x = Test.new
puts x.inc

y = Test.new
puts y.inc

#-------------

puts Test.inc
puts x.inc
puts y.inc

Hope that helps.

James Edward Gray II