From: Jim Weirich <jweirich@...>
Date: 2003-08-05T09:26:39+09:00
Subject: Re: clearing a parameter in Ruby?

On Mon, 2003-08-04 at 13:36, Roy Patrick Tan wrote:
> Hi,
> 
> is it possible to write a method that can "clear" a parameter in Ruby? 
> That is can a write a method "push" such that for the code below:
> 
>     x = "Hello"
>     string_stack.push(x)
>     puts x
> 
> the output will be nil instead of "Hello"?

I don't recommend this (because I think I would get really annoyed if I
were using a library that did this).

But with the above disclaimer, you could do it this way:

  class Pusher
    def initialize
      @stack = Array.new
    end
  
    def push(&block)
      sym = block.call
      @stack.push(eval(sym.to_s, block))
      eval "#{sym.to_s} = nil", block
    end
  end

  s = Pusher.new
  x = "HI"
  s.push { :x }
  p x   # => nil

-- 
-- Jim Weirich       jweirich@one.net      http://onestepback.org
-----------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct, 
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)