From: Rick DeNatale <rick.denatale@...>
Date: 2007-11-16T06:28:05+09:00
Subject: Re: instance variables as class variable ?

On Nov 15, 2007 3:15 PM, wbsurfver@yahoo.com <wbsurfver@gmail.com> wrote:
>
> I'm trying to get a handle on why the following code works by printing
> out 'frog'
> because @x looks like instance variable syntax. I know that some of
> these things don't work the way I'd expect.
>
> class Test
>  @x = 'frog'
>
>   class << self
>   attr_reader :x
>   end
>
> end
>
> puts Test.x

Well it is an instance variable, of the class.  This is commonly
called a class instance variable, not to be confused with a class
variable.

Within the lexical scope of class..end self is the class, so @x is an
instance variable of the class.

Consider this:

class Test

    # self here is Test which holds the methods for its instances

    attr_reader :x   # this is actually a message sent to Test, which
defines an instance method
end

Now when you say
class Test
 class << self  # (which could also be class << Test)
      #self becomes the singleton class of Test.
     attr_reader :x # and here the attr_reader message is sent to
Test's singleton class
                              # resulting in an "instance method" in
the singleton class which is a
                              # class method of Test

 end
end



-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/