From: jweirich@...
Date: 2001-09-26T20:09:25+09:00
Subject: [ruby-talk:21716] Re: manipulating "immutable" objects such as Fixnum from within callbacks & al...

>>>>> "Guillaume" == Guillaume Cottenceau <gc@mandrakesoft.com> writes:

    Guillaume> Here's the problem: it happens often that you need to
    Guillaume> pass "references" to objects so that
    Guillaume> callbacks/functions/etc may modify these objects to
    Guillaume> their convenience, and you will need the modified value
    Guillaume> afterwards.

Not that I particularly recommend this approach, but the following
will actually work ...

   class Pointer
    def initialize(&block)
      @getter = eval("lambda { #{yield.id2name} }", block)
      @setter = eval("lambda { |value| #{yield.id2name} = value }", block)
    end
    def value
      @getter.call
    end
    def value=(new_value)
      @setter.call(new_value)
    end
  end

  def increment(a_pointer)
    a_pointer.value = a_pointer.value + 1
  end

  x = 1
  increment(Pointer.new{:x})
  puts x   # => 2

Truthfully, this borders on the bizarre.  I've never found a need for
this in real life code.  For some background, see ...

    http://c2.com/cgi/wiki?SinisterSchemeSampleInRuby

-- 
-- Jim Weirich     jweirich@one.net    http://w3.one.net/~jweirich
---------------------------------------------------------------------
"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)