From: David Alan Black <dblack@...>
Date: 2002-05-02T23:58:27+09:00
Subject: Re: A scoping issue

Hello --

On Thu, 2 May 2002, Harry Ohlsen wrote:

> I'm trying to write a class that constructs a Tk
> dialog and am hitting an issue to do with the scope
> of instance variables.
>
> As part of the processing, what I want is something
> similar to the following code (I've made it non-Tk,
> to show up the essence of the problem) ...
>
> class A
>    def initialize(&block)
>       @code = block
>    end
> end
>
> class B
>    def initialize
>       @x = 123
>
>       a = A.new(proc { puts @x })
>       a.execute
>    end
> end
>
> The problem is that, of course, the reference to @x
> assumes it's an instance variable of class A, rather
> than the one from class B, in the outer scope.
>
> Is there some way I can get the block passed to the
> A.new to end up with the @x from the instance of B
> that I'm constructing?

It looks like you're sending a proc as a regular argument,
rather than as a block, but A#initialize is expecting a
block.  I've tweaked it so that it's all block-wise.
Also I've added some tracer variables, just to make
stuff visible.  Here's the result:

  class A
     attr_reader :code
     def initialize(&block)
	@code = block
     end
  end

  class B
     attr_reader :a
     def initialize
	@x = 123
	@a = A.new { puts @x }
     end
  end

  B.new.a.code.call  # => 123


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav