From: Patrick Hurley <phurley@...>
Date: 2005-03-31T00:20:08+09:00
Subject: Re: Defining a Class Accessor

On Wed, 30 Mar 2005 23:53:25 +0900, James Edward Gray II
<james@grayproductions.net> wrote:
> I was playing around with an idea in another thread and ran into a
> surprise.  Can anyone explain the following to me?
> 
> irb(main):015:0> class Module
> irb(main):016:1> def cattr_accessor( *symbols )
> irb(main):017:2>     symbols.each do |sym|
> irb(main):018:3*         eval "def self.#{sym}(  ) @@#{sym} end
> irb(main):019:3"               def self.#{sym}=( value ) @@#{sym} =
> value end"
> irb(main):020:3>     end
> irb(main):021:2> end
> irb(main):022:1> end
> => nil
> irb(main):023:0> class Accessor
> irb(main):024:1> cattr_accessor :one, :two
> irb(main):025:1> def self.fetch_one(  )
> irb(main):026:2>     @@one
> irb(main):027:2> end
> irb(main):028:1> end
> => nil
> irb(main):029:0> Accessor.one = "James"
> => "James"
> irb(main):030:0> Accessor.two = "Gray"
> => "Gray"
> irb(main):031:0> Accessor.one
> => "James"
> irb(main):032:0> Accessor.two
> => "Gray"
> irb(main):033:0> Accessor.fetch_one
> NameError: uninitialized class variable @@one in Accessor
>          from (irb):26:in `fetch_one'
>          from (irb):33
>          from (null):0
> 
> Everything works as expected, save fetch_one().  Why does it not return
> "James"?
> 
> Thanks.
> 
> James Edward Gray II
> 
> 

I have been playing with this myself, your @@one is in Module not in
Accessor -- try changing your eval to class_eval:

class Module
  def cattr_accessor( *symbols )
    symbols.each do |sym|
        self.class_eval <<EVAL
          def self.#{sym}()
            @@#{sym}
          end

          def self.#{sym}=( value )
            @@#{sym} = value
          end
EVAL
    end
  end
end